What Parts of the Eye Can Be Transplanted? - American Academy of Ophthalmology What Parts of the Eye Can Be Transplanted? Mar. 03, 2014 You may have heard about someone having an "eye transplant," but what exactly does that mean? As it turns out, only one part of the eye can be transplanted. Medical science has no way to transplant whole eyes. When someone receives an "eye transplant," they are being given a donor cornea, the clear front part of the eye. Your eye is a complex organ connected to your brain by the optic nerve. The optic nerve sends visual signals from the eye to the brain, where they are interpreted as images. The optic nerve is relatively small, varying in length between 1.3 and 2.2 inches, and at its widest point, inside your cranial cavity, it is still less than one-fifth of an inch wide. Yet the optic nerve is made up of more than one million tiny nerve fibers, much like a fiber optic cable. Once these nerve fibers are cut, they cannot be reconnected. That is why it's impossible to transplant a whole eye.

Even if a surgeon could implant the eye into the eye socket, the eye still would not be able to transmit signals to the brain through the optic nerve and thus would not provide sight. By contrast, corneal transplantation is not only possible, it is a procedure more than a century old. A healthy, clear cornea is necessary for good vision. If your cornea is injured or affected by disease, it may become swollen or scarred. A cornea with scarring, swelling or an irregular shape can cause glare or blurred vision. In a corneal transplant, the damaged or unhealthy cornea tissue is removed and clear donor cornea tissue is put in its place. Read more about corneal transplant surgery options . While corneal transplants are the most common type of eye-related transplantation, it is not the only one. Surgeons have also been able to successfully perform eyelash transplantation. However, the procedure carries significant risks, including scarring, and is not recommended as a cosmetic procedure. In patients suffering from disorders of the sclera or the conjunctiva (the external eye), doctors have been able to transplant amniotic membranes which have aided in the healing and regeneration of ocular surface tissues.

Doctors continue to explore whether it is possible to transplant other parts of the eye. In July 2010, French doctors announced that they had transplanted eye lids and tear ducts as part of a full-face transplant for a man with a genetic disorder. Researchers are also focusing on how to replace damaged retinal cells with healthy transplants. In fact, it has been shown in recent clinical trials that human stem cells can be cultivated to become retinal pigment epithelium (RPE) cells. In the near future, we can expect RPE transplants. This is good news for people suffering from macular degeneration and Stargardt's Disease. Image Formation by Lenses and the Eye Image Formation by Lenses and the Eye Image formation by a lens depends upon the wave property called refraction. Refraction may be defined as the bending of waves when they enter a medium where their speed is different. Since the speed of light is slower in a glass lens than in air, a light ray will be bent upon entering and upon exiting a lens in a way that depends upon the shape and curvature of the lens. In the case of a converging lens such as the double convex lens shown below, parallel rays will be brought together at a point.

The distance from the lens to this principal focus point is called the focal length of the lens and will be designated by the symbol f. A converging lens may be used to project an image of a lighted object. For example, the converging lens in a slide projector is used to project an image of a photographic slide on a screen, and the converging lens in the eye of the viewer in turn projects an image of the screen on the retina in the back of the eye. There is a geometrical relationship between the focal length of a lens (f), the distance from the lens to the bright object (o) and the distance from the lens to the projected image (i). The relationship between the distances illustrated in Figure 2 can be expressed as This relationship will be used to determine the focal length of a glass lens, and will be used as the basis for a qualitative investigation of image formation by the eye with the use of a large eye model. 1. Position the lens and white screen on the optical bench and place them so that the distance from the lighted "object" to the lens can be measured on the bench scale. Adjust the screen to get a clear image.

Determine the object distance and image distance, o and i, and calculate the focal length from the lens relationship. Describe the appearance of the image, compared to the object (e.g, larger, smaller, erect, inverted). Adjust the object distance to a different value and repeat the process with a different set of measurements. 2. What is the average of your focal length measurements, expressed in meters? 3. The lens strength in diopters is defined as S = 1/f(in meters). The unit is 1/m but this unit is commonly called a "diopter". What is the strength of your lens in diopters? Note: Converging lenses are listed as + and diverging lenses as - when diopter numbers are quoted. Prescriptions for eyeglasses are usually expressed in diopters. I. Image formation by a lens; determination of focal length. 4. What is the diopter number of a lens of focal length 0.05 meters? What is the focal length of a +7 diopter lens? 5.

Using the average value of your focal length measurements, calculate the image distance i if the object distance is 1.5 x your focal length (e.g, if your measured focal length were 10 cm, you would do the calculation for an object distance of 15 cm). For this arrangement, the image distance and linear magnification of the image are given by Measure the height of your object and predict the size of the image which would be formed with the object placed as described above. Now make the actual measurements of image distance and image size and compare them with your predictions. Predictions Measured object size h = _______ cm Measured image distance i = _______ cm Measured image size = h' = _______ cm Predicted image size h' = _______ cm II. Investigation of image formation by the eye. The figure shows a sketch of the eye model. At the beginning of the experiment the retina should be in the middle, or "normal eye" position. The model should be filled with water to a height which covers the fixed lens of the eye model. This fixed lens of the eye model represents the cornea. In addition to the cornea, the human eye has another internal lens. 1.

Place the object light about two meters away from the eye model so that light passes through the eye's lens and falls on the retina. Find a lens to place in the holder inside the water of the eye model which will give you a clear image on the retina. This internal lens in the human eye has a variable focal length and is changed in shape to allow you to change your eye's focus from a distant object to a close one. This change of focus is called "accommodation". Lens strength for sharp image at 2 meters: _________ 2. Move the object to a distance 35 cm from the front lens. To illustrate accommodation, and try to find a lens to replace the lens in the water which will again give you a clear image on the retina. Then make small adjustments in the object distance to get the sharpest possible image and record the object distance and lens strength needed to achieve it. Lens strength for sharp image at 35 cm : _________ If you moved it away from 35 cm, record the data: Distance for sharpest focus _____________ Lens strength ___________ Note: You should now have a clear image on the retina.

The positions of the object and the eye model should be kept fixed for the next two steps of the experiment. 3. To simulate far-sightedness (hyperopia), move the retina of the eye model to the forward position. The light rays should be seen to converge toward a point behind the retina. Find a corrective lens for this defect. (Lenses for correction must be positioned in the slots outside the eye model.). Diopter number for best correction ___________ 4. To simulate near-sightedness (myopia), move the retina to the rear. The light rays should be seen to converge toward a point in front of the retina. Find a corrective lens for this defect. Corrective lens _______________ 5. Remove the corrective lens from the front of the near-sighted eye model and replace it with the lens holder which has a metal plate with an aperture in it. Describe any changes in the image quality when this aperture is placed at the front of the eye model. Would a nearsighted person see clearer images in dim light or in bright light? Why do nearsighted persons squint? 6. The human eye is relaxed when it is focused on distant objects.

From your experience in this lab, does the lens focal length approach a maximum or a minimum when your eye relaxes? Would this imply that the eye's lens is more rounded or less rounded when the eye muscle is relaxed? Equipment: Image Formation Corneal Transplantation - procedure, recovery, blood, removal, complications, adults, time, infection Corneal Transplantation Corneal transplantation Definition In corneal transplant, also known as keratoplasty, a patient's damaged cornea is replaced by the cornea from the eye of a human cadaver. This is the most common type of human transplant surgery and has the highest success rate. Eye banks acquire and store eyes from donors to supply the need for transplant corneas. Purpose Corneal transplant is used when vision is lost because the cornea has been damaged by disease or traumatic injury, and there are no other viable options. Some of the conditions that might require corneal transplant include the bulging outward of the cornea (keratoconus), a malfunction of the cornea's inner layer (Fuchs' dystrophy), and painful corneal swelling (pseudophakic bullous keratopathy).

Other conditions that might make a corneal transplant necessary are tissue growth on the cornea (pterygium) and Stevens-Johnson syndrome, a skin disorder that can affect the eyes. Some of these conditions cause cloudiness of the cornea; others alter its natural curvature, which also can reduce vision quality. Injury to the cornea can occur because of chemical burns, mechanical trauma, or infection by viruses, bacteria, fungi, or protozoa. The herpes virus produces one of the more common infections leading to corneal transplant. Corneal transplants are used only when damage to the cornea is too severe to be treated with corrective lenses. Occasionally, corneal transplant is combined with other eye surgery such as cataract surgery to solve multiple eye problems with one procedure. Demographics The Eye Bank Association of America reported that corneal transplant recipients range in age from nine days to 103 years. More than 40,000 corneal transplants are performed in the United States each year. The cost is usually covered in part by Medicare and health insurers, although the patient might be required to incur part of the cost for the procedure. All eye tissue is donated.

It is illegal to buy or sell human tissue. Description The cornea is the transparent layer of tissue at the front of the eye. It is composed almost entirely of a special In a corneal transplant, the eye is held open with a speculum (A). A laser is used to make an initial cut in the existing cornea (B). The surgeon uses scissors to remove it (C), and a donor cornea is placed (D). It is stitched with very fine sutures (E). ( Illustration by GGS Inc. ) type of collagen. It normally contains no blood vessels, but because it contains nerve endings, cornea damage can be very painful. In a corneal transplant, a disc of tissue is removed from the center of the eye and replaced by a corresponding disc from a donor eye. The circular incision is made using an instrument called a trephine, which resembles a cookie cutter. In one form of corneal transplant, penetrating keratoplasty (PK), the disc removed is the entire thickness of the cornea and so is the replacement disc. The donor cornea is attached with extremely fine sutures.

Surgery can be performed under anesthesia that is confined to one area of the body while the patient is awake (local anesthesia) or under anesthesia that places the entire body of the patient in a state of unconsciousness (general anesthesia). Surgery requires 30–90 minutes. Over 90% of all corneal transplants in the United States are PK. In lamellar keratoplasty (LK), only the outer layer of the cornea is removed and replaced. LK has many advantages, including early suture removal and decreased infection risk. It is not as widely used as PK, however, because it is more time consuming and requires much greater technical ability by the surgeon. A less common but related procedure called epikeratophakia involves suturing the donor cornea directly onto the surface of the existing host cornea. The only tissue removed from the host is the extremely thin epithelial cell layer on the outside of the host cornea. There is no permanent damage to the host cornea, and this procedure can be reversed. This procedure is mostly performed on children. In adults, the use of contact lenses can usually achieve the same goals.

Diagnosis/Preparation Surgeons may discuss the need for corneal transplants after other viable options to remedy corneal trauma or disease have been discussed. No special preparation for corneal transplant is needed. Some ophthalmologists may request that the patient have a complete physical examination before surgery. Any active eye infection or eye inflammation usually needs to be brought under control before surgery. The patient may also be asked to skip breakfast on the day of surgery. Aftercare Corneal transplant is often performed on an outpatient basis, although some patients need brief hospitalization after surgery. The patient will wear an eye patch at least overnight. An eye shield or glasses must be worn to protect the eye until the surgical wound has healed. Eye drops will be prescribed for the patient to use for several weeks after surgery. Some patients require medication for at least a year. These drops include antibiotics to prevent infection as well as corticosteroids to reduce inflammation and prevent graft rejection. For the first few days after surgery, the eye may feel scratchy and irritated. Vision will be somewhat blurry for as long as several months. Sutures are often left in place for six months, and occasionally for as long as two years.

Some surgeons may prescribe rigid contact lenses to reduce corneal astigmatism that follows corneal transplant. Risks Corneal transplants are highly successful, with over 90% of the operations in United States achieving restoration of sight. However, there is always some risk associated with any surgery. Complications that can occur include infection, glaucoma, retinal detachment, cataract formation, and rejection. Graft rejection occurs in 5–30% of patients, a complication possible with any procedure involving tissue transplantation from another person (allograft). Allograft rejection results from a reaction of the patient's immune system to the donor tissue. Cell surface proteins called histocompatibility antigens trigger this reaction. These antigens are often associated with vascular tissue (blood vessels) within the graft tissue. Because the cornea normally contains no blood vessels, it experiences a very low rate of rejection. Generally, blood typing and tissue typing are not needed in corneal transplants, and no close match between donor and recipient is required. However, the Collaborative Corneal Transplantation Study found that patients at high risk for rejection could benefit from receiving corneas from a donor with a matching blood type.

Symptoms of rejection include persistent discomfort, sensitivity to light, redness, or a change in vision. If a rejection reaction does occur, it can usually be blocked by steroid treatment. Rejection reactions may become noticeable within weeks after surgery, but may not occur until 10 or even 20 years after the transplant. When full rejection does occur, the surgery will usually need to be repeated. Although the cornea is not normally vascular, some corneal diseases cause vascularization (the growth of blood vessels) into the cornea. In patients with these conditions, careful testing of both donor and recipient is performed just as in transplantation of other organs and tissues such as hearts, kidneys, and bone marrow. In such patients, repeated surgery is sometimes necessary in order to achieve a successful transplant. Normal results Patients can expect restored vision after the healing process is complete. In some patients, this might take as long as a year. Patients with keratoconus, corneal scars, early bullous keratopathy, or corneal stromal dystrophies have the highest rate of transplant success. Corneal transplants for keratoconus patients have a success rate of more than 90%.

Morbidity and mortality rates While there is risk involved with any surgery, corneal transplants are relatively safe. In 2001, there was some concern about cornea donors transmitting Creutzfeldt-Jakob disease, a fatal bone-deteriorating disease, after questions of infection arose in Europe. A study showed the risk of transmission in the United States was small, as was any infection risk from cornea donors. Currently, cornea donors are screened using medical standards of the Eye Bank Association of America. These guidelines restrict donors who died from unknown causes, or suffered from immune deficiency diseases, hepatitis, and other infectious diseases. Transplant recipients may have to receive another transplant if the first is unsuccessful or if, after a number of years, the disease returns. Alternatives An increasingly popular alternative to corneal transplants is phototherapeutic keratectomy (PTK). This technique is now used to treat corneal scars and dystrophies, and some infections. Surgeons use an excimer laser and a computer to vaporize diseased tissue, leaving a smooth surface. New tissue begins growing immediately and recovery takes only a few days.

Patients must be carefully selected, however, and success is greatest if damage is restricted to the cornea's top layer. Intrastromal corneal rings are implantable devices that could be used for some keratoconus patients. The rings are implanted and the procedure is reversible. However, not much is known about long-term stability. Some companies also are developing synthetic corneas that are implanted using synthetic penetrating keratoplasty. This procedure may become more widely used for high-risk patients and those with severe chemical burns. Resources books Boruchoff, S. Arthur, and Richard A. Thoft. "Keratoplasty: Lamellar and Penetrating." In The Cornea, edited by Gilbert Smolin and Richard A. Thoft. Boston: Little, Brown and Co., 1994. Brightbill, Frederick S., ed. Corneal Surgery. St. Louis: Mosby, 1993. Bruner, William E., Walter J. Stark, and A. Edward Maumenee. Manual of Corneal Surgery. New York: Churchill Livingstone, 1987. Miller, Stephen J. H.

Parsons' Diseases of the Eye, 18th ed. New York: Churchill Livingstone, 1990. Vaughan, Daniel, ed. General Ophthalmology, 14th ed. Stamford: Appleton & Lange, 1995. periodicals Kennedy, R. H., et al. "Eye Banking and Screening for Creutzfeldt-Jakob Disease." Archives of Ophthalmology 119 (May 2001): 721–6. Watson, B. C., and G. L. White Jr. "Corneal Transplantation." American Family Physician 54 (Nov. 1996): 1945–48. organizations American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. . Eye Bank Association of America. 1015 Eighteenth Street NW, Suite 1010, Washington, D.C. 20036. (202) 775-4999. .

other Asbell, Penny A., and Syed M. Ahmad. "New Techniques in Corneal Transplant." Review of Ophthalmology, May 15, 2002 [cited February 20, 2003]. . Cimberle, Michela. "New Type of Artificial Cornea Performs Better than Donor Grafts in High-Risk Cases." Ocular Surgery News, June 1, 2002 [cited February 23, 2003]. . "Collaborative Corneal Transplantation Studies." National Eye Institute, October 21, 1999 [cited February 25, 2003]. . "Corneal Transplantation." Merck Manual of Diagnosis and Therapy, [cited February 25, 2003]. . "Facts About the Cornea and Corneal Disease." National Eye Institute, June 2001 [cited March 4, 2003]. . Victor Leipzig, PhD Mary Bekker WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

Corneal transplants are performed by an ophthalmologist, who is a corneal specialist and is expert at transplants and corneal diseases. Patients might be referred to a corneal specialist by their ophthalmologist or optometrist. Surgery is performed in a hospital setting, usually on an outpatient basis. Some surgeons may also perform the procedure at an ambulatory surgery center designed for outpatient procedures. QUESTIONS TO ASK THE DOCTOR Are there any alternatives that might restore my vision? What is the chance of rejection? How am I matched with the donor corneas? What is the screening process for donors? What physical restrictions will I have during the healing process? What are the chances of eye injury causing rejection? If the transplant is successful, how long will it be until vision is restored? Will I ever have to have another transplant?

Also read article about Corneal Transplantation from Wikipedia User Contributions: Cataract Surgery Basics - All About Vision [Video] On this page: Cataract surgery video Sometime after age 50, most of us are likely to hear our eye doctor say, "You have cataracts." A cataract is a clouding of the lens inside the eye, causing vision loss that cannot be corrected with glasses, contact lenses or corneal refractive surgery like LASIK . As frightening as cataracts might sound, modern cataract surgery usually can restore vision lost to cataracts  and often can reduce your dependence on eyeglasses as well. Cataract Prevalence After Age 50 (U.S.) Most cataracts are associated with the aging process and are common among older Americans. In fact, according to the National Eye Institute (NEI), 68.3 percent of Americans 80 and older had cataracts in 2010. And the prevalence of cataracts in the U.S. is expected to grow significantly in the years ahead, due in part to the aging of the population.

In 2010, roughly 24.4 million Americans had cataracts, and that number is projected to grow to 50.2 million by the year 2050, according to NEI. Thankfully, modern cataract surgery is one of the safest and most effective surgical procedures performed today. More than 3 million cataract surgeries are performed in the United States every year, with the vast majority of these procedures produce excellent visual outcomes. Cataract Surgery Basics In cataract surgery, the lens inside your eye that has become cloudy is removed and replaced with an artificial lens (called an intraocular lens, or IOL ) to restore clear vision. Best Candidates blurred vision, clouded vision, light sensitivity, dim colors Procedure time: about 15 minutes Typical results: long-lasting clear vision (at all distances with presbyopia-correcting IOLs) Recovery time: about a month The procedure typically is performed on an outpatient basis and does not require an overnight stay in a hospital or other care facility. Most modern cataract procedures involve the use of a high-frequency ultrasound device that breaks up the cloudy lens into small pieces, which are then gently removed from the eye with suction.

This procedure, called phacoemulsification or "phaco," can be performed with smaller incisions than previous surgical techniques for cataract removal, promoting faster healing and reducing the risk of cataract surgery complications , such as a retinal detachment . After all remnants of the cloudy lens have been removed from your eye, the cataract surgeon inserts a clear intraocular lens, positioning it securely behind the iris and pupil , in the same location your natural lens occupied. (In special cases, an IOL might be placed in front of the iris and pupil, but this is less common.) The surgeon then completes the cataract removal and IOL implantation procedure by closing the incision in your eye (a stitch may or may not be needed), and a protective shield is placed over the eye to keep it safe in the early stages of your cataract surgery recovery. Recommended For You Questions about cataracts? Find all the answers in My Cataract Journey Laser Cataract Surgery Recently, a number of femtosecond lasers  similar to the lasers used to create the corneal flap in all-laser LASIK  have been approved by the FDA for use in cataract surgery performed in the United States.

Watch this video about how cataract surgery works. These lasers have gained approval for the following steps in cataract surgery, reducing the need for surgical blades and other hand-held tools: Creating corneal incisions to allow the surgeon access to the lens Removing the anterior capsule of the lens Fragmenting the cataract (so less phaco energy is required to break it up and remove it) Creating peripheral corneal incisions to reduce astigmatism (when needed) Laser cataract surgery (or, more accurately, laser-assisted cataract surgery) is fairly new and significantly increases cataract surgery cost , primarily because the laser can cost from $300,000 to $500,000 for a surgeon to purchase and there are other significant costs associated with the use and maintenance of this technology. While studies have shown that lasers can improve accuracy during certain steps of cataract surgery, they may not necessarily improve cataract surgery safety, recovery time and visual outcomes in every case. For the latest information about laser cataract surgery, ask your eye doctor during your preoperative eye exam and cataract surgery consultation.

Cataract Surgery News Image: Kang Zhang Scientists Working On Eye Drops To Dissolve Cataracts August 2015  Cataract surgery is proven to be safe and effective, with a low risk of serious complications. But wouldn't it be great if eye drops could dissolve cataracts without the need for costly surgery? For one thing, maybe they could help people who live in areas without surgeons or affordable health care. In a recent study of congenital cataracts (meaning, cataracts that are present from birth), University of California San Diego researchers found that a molecule called lanosterol prevents cataract-causing proteins from adhering to each other, keeping the human lens clear. But if the molecule is abnormal because of a gene mutation, the proteins will adhere and make the lens cloudy. Sidebar continued >> The researchers created eye drops containing lanosterol, tested them in rabbit eye lenses and found the lenses were clearer after a few days. In live dogs' eyes the drops also reduced the effect of their cataracts. The drops don't work as well as surgery, because they don't eliminate the cloudiness in the lens  they only reduce it.

Further testing may produce a more effective formula, but that will take time. Still, the potential exists for cataract-dissolving drops to be used routinely someday not just in animals, but also in humans.  L.S. Preparing For Cataract Surgery And Choosing An IOL Prior to cataract surgery, your optometrist and/or ophthalmologist will perform a comprehensive eye exam to check the overall health of your eyes, evaluate whether there are reasons why you should not have surgery and identify any risk factors you might have. A refraction also will be performed to accurately determine the amount of nearsightedness , farsightedness and/or astigmatism you have prior to surgery. Additional measurements of your eyes will be taken to determine the curvature of your cornea and the length of your eye. These measurements are essential to help your cataract surgeon select the proper power of the intraocular lens and give you the best vision possible after surgery. Today you have many types of IOLs to choose from for your cataract surgery, depending on your specific needs. In addition to IOLs that correct nearsightedness and farsightedness, there are now toric IOLs that correct astigmatism as well.

If you don't mind wearing glasses after cataract surgery, a monofocal lens implant usually is used. Often, only part-time use of reading glasses is needed after cataract surgery with monofocal IOLs. But if prescription eyeglasses are needed (which often is the case if you only need cataract surgery in one eye), your eye doctor typically will prescribe new glasses for you approximately one month after surgery. If you like the idea of being less dependent on glasses after cataract surgery, one way to correct presbyopia and reduce your need for reading glasses is to have your cataract surgeon adjust the power of one of your monofocal IOLs (assuming you have cataract surgery performed in both eyes) to give you a monovision correction, similar to monovision with contact lenses . Another option is to choose one of a variety of advanced presbyopia-correcting IOLs to improve your reading vision without sacrificing your distance vision. Presbyopia-correcting IOLs include accommodating IOLs and multifocal IOLs ; both types are designed to provide a greater range of vision after cataract surgery than conventional monofocal IOLs.

Be aware that not everyone is a good candidate for these premium IOLs, and choosing a presbyopia-correcting IOL will increase the out-of-pocket cost of your cataract surgery, since the added cost of these advanced lens implants is not covered by Medicare or other insurance plans. Prior to cataract surgery, in addition to discussing the different types of IOLs, you will be advised about what to expect before, during and after your procedure. This information  which may be presented orally, in writing, via a video presentation or a combination of all three  is meant to help you make an informed decision about whether to proceed with surgery. If you have any questions or concerns about cataract surgery, be sure to discuss them with your eye doctor and cataract surgeon prior to signing "informed consent" documents authorizing surgery. Also, discuss with your eye doctor all medications you are taking, including non-prescription ("over-the-counter") formulations and nutritional supplements. Some medications and supplements can increase your risk of cataract surgery complications and might need to be discontinued prior to surgery. Ask your doctor for details.

Cataract Surgery News Some People May Need Cataract Surgery Sooner After LASIK March 2015  Researchers in Japan discovered something interesting about people having cataract surgery after having had LASIK: they may need cataract surgery sooner. In the retrospective study, three groups of patients were evaluated: Sidebar continued >> LASIK Group: Forty consecutive patients scheduled for cataract surgery who had previously undergone LASIK. Control Group 1: A group of 606 patients having cataract surgery who did not previously have LASIK, but whose eyes were matched to the LASIK group for axial length (front-to-back length of the eyeball, a factor in the degree of myopia). Control Group 2: A group of 3,642 patients having cataract surgery whose eyes were not matched to those of the LASIK group for axial length. The mean age at cataract surgery for patients who previously had LASIK was 54.6 years  about 10 years younger than those in control group 1 (matched axial length) and about 15 years younger that those in control group 2 (unmatched for axial length).

Also, 70 percent of patients in the LASIK group were men, a significantly higher percentage than in the control groups. And the rate of corneal higher-order aberrations was significantly higher in the LASIK group than in the control groups. The study authors concluded that patients with longer-than-average eyeball length (associated with higher myopia) and an increase in corneal higher-order aberrations might need to have cataract surgery performed earlier if they have previously undergone LASIK surgery. A report of the study appeared in February in Journal of Cataract & Refractive Surgery.  G.H. Cataract Surgery Recovery An uncomplicated cataract surgery typically lasts only about 15 minutes. But expect to be at the surgical center for 90 minutes or longer, because extra time is needed to prepare you for surgery (dilating your pupil; administering preoperative medication) and for a brief post-operative evaluation and instructions about your cataract surgery recovery before you leave. You must have someone drive you home after cataract surgery; do not attempt to drive until you have visited your eye doctor the day after surgery and he or she tests your vision and confirms that you are safe to drive.

You will be prescribed medicated eye drops to use several times each day for a few weeks after cataract surgery. You also must wear your protective eye shield while sleeping or napping for about a week after surgery. To protect your eyes from sunlight and other bright light as your eye recovers, you will be given a special pair of post-operative sunglasses . Also, many centers require someone to be with you after cataract surgery if you received anesthesia. Be sure to ask about this requirement prior to your cataract procedure so you are prepared for surgery day. While your eye heals, you might experience some eye redness and blurred vision during the first few days or even weeks following the procedure. During at least the first week of your recovery, it is essential that you avoid: Strenuous activity and heavy lifting (nothing over 25 pounds). Bending, exercising and similar activities that might stress your eye while it is healing. Water that might splash into your eye and cause infection. Keep your eye closed while showering or bathing. Also, avoid swimming or hot tubs for at least two weeks. Any activity that would expose your healing eye to dust, grime or other infection-causing contaminants.

Your cataract surgeon may give you other instructions and recommendations for your cataract surgery recovery, depending on your specific needs and the outcome of your procedure. If you have any questions at any time after cataract surgery, call your eye doctor for advice. If you need cataract surgery in both eyes, your surgeon typically will prefer that you wait one to three weeks between procedures, so your first eye has healed sufficiently and you have good vision in that eye before the second surgery is performed. Eyes Eyes Los ojos Eyes: Small But Mighty We depend on sight more than any other of our senses to maneuver through the space around us. In a single glance, lasting a fraction of a second, our eyes work with our brains to tell us the size, shape, color, and texture of an object. They let us know how close it is, whether it's standing still or coming toward us, and how quickly it's moving. Every day, our eyes give us messages that help us understand the world around us. Although the eyes are small compared with most of the body's other organs, their structure is incredibly complex. The eyes work together to perceive depth, enabling us to judge distance and the size of objects to help us move around them.

Not only do the two eyes work together, they also work with the brain, muscles, and nerves to produce complicated visual images and messages. And our eyes constantly adapt to the changing environment — for example, they are able to adjust so that we can easily move around in a nearly dark room or bright sunlight. To understand more about how the eyes work, it's important to know about the structures that make up the eye and about conditions and diseases that can interfere with vision. continue The Basics on Eyes Only part of the eye is visible in a person's face. The whole eye — the eyeball — is about the size and shape of a ping-pong ball. The eye — both the parts that are visible and those that aren't — is extremely delicate. The body has several ways of protecting this vulnerable organ. The eyeball sits in the eye socket (also called the orbit) in a person's skull, where it is surrounded by bone. The visible part of the eye is protected by the eyelids and the eyelashes, which keep dirt, dust, and even harmful bright light out of the eye.

Our eyes are also protected by our tears, which moisten the eyes and clean out dirt, dust, and other irritants that get past the defenses of our eyelashes and eyelids. Tears also help protect the eyes against infection. Every time we blink, our eyelids spread a layer of moisture over the cornea, which covers the front of the eye. The lacrimal (pronounced: LAK-ruh-mul) glands in the upper outer corner of each eye socket produce tears. After they've done their job moistening the eyes, the tears flow into canals in the eyelids, which drain into the lacrimal sac, a pouch in the lower inner corner of each eye socket. Tears then exit through a passage that leads to the nose. For you to see, the eye has to move. Six muscles, called extraocular (pronounced: eks-truh-OK-yuh-ler) muscles, surround the eyeball in the skull. These muscles act like the strings on a puppet, moving the eye in different directions. The muscles of each eye normally move together at the same time, allowing the two eyes to remain aligned.

The wall of a person's eyeball is made up of three layers, rather like the layers on an onion: The sclera (pronounced: SLEER-uh) is the outermost protective layer. This tough, fibrous tissue surrounds the eyeball and attaches to the cornea, which is the clear front surface of the eye. What we see as the white of the eye is the sclera. The conjunctiva (pronounced: kon-junk-TY-vuh) a clear skin layer that protects the eye from becoming dry, sits over the sclera and also covers the inner surface of the eyelid. The choroid (pronounced: KOR-oyd) is the middle layer that contains blood vessels that deliver oxygen and nutrients to the inside parts of the eye. The retina (pronounced: RET-nuh), the innermost of the three layers, lines the inside of the eyeball. The retina is a soft, light-sensitive layer of nervous system tissue. The optic nerve carries signals from the retina to the brain, which interprets them as visual images. The space in the center of the eyeball is filled with a clear jelly-like material called the vitreous (pronounced: VIH-tree-us) humor.

This material allows light to pass through to the retina. It also helps the eye keep its round shape. previous continue How We See Vision is the process by which images captured by the eye are interpreted by the brain, and the visible part of the eye is where the process of sight begins. On the front surface of the eye is the see-through, circle-shaped cornea. You can't see a person's cornea the way you can see the colored part of the eye behind it — the cornea is like a clear window that focuses light into the eye. Behind the cornea is a watery fluid called the aqueous humor. The cornea and aqueous humor form an outer lens that refracts (bends) light on its way into the eye. This is where most of the eye's focusing work is done. The colored circular membrane in the eye just behind the cornea is called the iris. The iris controls the amount of light entering the eye through the pupil, which is the opening in the center of the iris that looks like a tiny black circle.

Like a camera shutter, which controls the amount of light coming in to prevent both over- and under-exposure, the iris becomes wider and narrower, changing the size of the pupil to control the amount of light entering the eye. The pupil gets bigger when more light is needed to see better and smaller when there's plenty of light. The eye's lens sits just behind the iris. Just like a camera lens, the eye's lens focuses light to form sharp, clear images. Light that has been focused through the cornea and aqueous humor hits the lens, which then focuses it further, sending the light rays through the vitreous humor and onto the retina. To focus on objects clearly at varying distances, the eye's lens needs to change shape. The ciliary (pronounced: SIL-ee-air-ee) body contains the muscular structure in the eye that changes the shape of the eye's lens. In people who have normal vision, the ciliary body flattens the lens enough to bring objects into focus at a distance of 20 feet (6 meters) or more. To see closer objects, this muscle contracts to thicken the lens.

Young children can see objects at very close range; many people over 45 have to hold objects farther and farther away to see them clearly. This is because the lens becomes less elastic as we age. The retina (the soft, light-sensitive layer of tissue that lines the back of the eyeball wall) is made up of millions of light receptors. These are called rods and cones. Rods are much more sensitive to light than cones. Each eye has about 120 million rods that help us see in dim light and detect shades of gray, but they cannot distinguish colors. In comparison, the 6 million cones in each eye allow us to see in bright light, and they also sense color and detail. The macula (pronounced: MAK-yuh-luh) is a small, specialized area on the retina. The macula helps our eyes see fine details when we look directly at an object. It contains mainly cones and few rods. When focused light is projected onto the retina, it stimulates the rods and cones. The retina then sends nerve signals through the back of the eye to the optic nerve. The optic nerve carries these signals to the brain, which interprets them as visual images.

The portion of the brain that processes visual input and interprets the messages that the eye sends is called the visual cortex. Most people use both eyes to see an object. This is called binocular vision. Through binocular vision, images are formed on the retina of each eye. These images are slightly different, because the object is being viewed from slightly different angles. Nerve signals representing each image are sent to the brain, where they are interpreted as two views of the same object. Some of the nerve fibers from each eye cross, so each side of the brain receives messages from both eyes. Through experience, the brain learns to judge the distance of an object by the degree of difference in the images it receives from the two eyes. This ability to sense distance is called depth perception. Our vision is a fine-tuned process. All the parts of the eye — and the brain — need to work together so a person can see correctly. Because the eye's structure is so complex, though, a lot of things can go wrong. previous continue Things That Can Go Wrong With the Eyes and Vision Some of the most common eye problems are called refractive errors. These are the problems that eye doctors check for routinely in your vision test.

Refraction means bending of light rays to focus the light coming from an image. Refractive errors are problems with the focusing of the eye, which causes the image you see to be blurred. Refractive errors include: Astigmatism (pronounced: uh-STIG-muh-tih-zum). In astigmatism, there's a problem with the curve of the cornea. This causes part of the eye's image to be blurry. Corrective lenses such as contact lenses or glasses can usually correct vision in people with astigmatism. Myopia (pronounced: my-OP-ee-uh). Also called nearsightedness or shortsightedness, myopia occurs when the eye focuses the image of an object in front of the retina instead of directly on it. In most cases, people can't see well far away, but can see objects clearly close up. The condition tends to get somewhat worse through childhood and adolescence, but stabilizes in adulthood. People with this condition may need to wear glasses or contacts to correct their vision. Laser eye surgery is now commonly used in adults to correct nearsightedness permanently by changing the shape of the cornea.

Laser surgery is not used for teens because the eye may still be growing and the refractive error changing. Hyperopia (pronounced: hy-per-OP-ee-uh). Also called farsightedness or longsightedness, hyperopia occurs when the incoming image is not focused on the retina, but behind it. This may make it difficult to see close objects clearly, with far-off objects seen more easily. Many younger children are hyperopic, but because of the ability of the eye to focus itself, may not need glasses to correct this. Glasses or contact lenses can correct this problem in kids and teens when needed. Some of the other eye problems that can affect teens include: Blindness. This is the loss of useful sight. Blindness can be temporary or permanent and it has many causes. Birth defects or damage to any portion of the eye, the optic nerve, or the area of the brain responsible for vision can lead to blindness. The visual impairment cannot be corrected with surgery or corrective lenses, and the condition can make it difficult to perform everyday activities. Diabetes and eye changes because of aging account for most blindness in adults in the United States. But eye injuries or eye trauma are the most common causes for blindness in kids and teens.

Color blindness. Color blindness is usually caused by problems in the pigments of the cones in the retina. Most people who are color-blind can see some colors. A person who is color-blind often confuses some colors with others, such as red and green. People can be born color-blind, or they may develop the condition over time. The most common form of color blindness is an inherited condition that affects boys much more often than girls. Color blindness cannot be corrected. Conjunctivitis (pronounced: kon-junk-tuh-VY-tus). Conjunctivitis refers to inflammation (redness, pain, and swelling) of the conjunctiva. One type of conjunctivitis, pinkeye, is a common contagious infection in which the eyes become pinkish red and watery, and pus may form. Pinkeye is usually treated with eyedrops. Conjunctivitis also can be due to allergies or from something that irritates the eye. Eye injuries . Injuries to the eye are one of the most common preventable causes of blindness. Eye injuries may be caused by irritants such as sand, dirt, or other foreign bodies on the eye's surface.

Chemicals or foreign bodies that become embedded in the eye can cause pain and loss of vision. Forceful blows to the eye can cause bleeding inside the eye and damage to the cornea, retina, and other important eye structures. Stye . This red, painful bump on the eyelid is caused by a backed-up oil gland. Styes are treated by applying warm compresses to allow them to drain. Sometimes antibiotic drops or ointments are necessary if it gets infected. Sometimes, a doctor may need to make a tiny cut in the eyelid to let out the clogged-up material. Wondering how to keep your eyes in excellent shape? One of the best things you can do for your eyes is to have them checked by your doctor whenever you have a physical examination. If you're having trouble seeing or you've been getting frequent headaches at the end of the day, make arrangements to have your eyes examined by an eye specialist. Human Eye | Tutorvista.com Top Human Eye One of the most complicated optical devices is the human eye. Let us see the construction of the human eye and then the mechanism of image formation. Human eye is spherical in shape and diameter of about 2.5cm.

Sclerotic is a tough, opaque and white substance forming the outermost coating of the yet. The front portion is sharply curved and covered by a transparent protective membrane called the 'cornea'. Inner to the sclerotic there is a layer of black tissue called as choroids consisting of a mass of blood vessels, which nourishes the eye. The black color does not reflect the light and hence rules out the blurring of image by reflection within the eyeball. Behind the cornea, the space is filled with a liquid called the aqueous humor and behind that a crystalline lens. 'Iris' is a muscular diaphragm lying between the aqueous humor and the crystalline lens. Iris has an adjustable opening in the middle called the pupil of the eye. The pupil appears black because all the light entering is absorbed by the 'retina', which covers the inside of the rear part of the ball. Iris controls the amount of light emerges because the retina absorbs nearly all the light, which falls upon it. This is done by varying the aperture of the pupil with the help of the iris. In dim light the iris dilates the pupil and so that more light can enter in. when the light is bright the pupil contracts.

The crystalline lens divides the eyeball into two chambers. The chamber between the cornea and the lens is called the anterior chamber filled with a fluid called aqueous humour while the chamber between the lens and the retina is called the posterior chamber which is filled with a transparent gelatinous substance called vitreous humour. The refractive indices of the cornea, pupil lens and fluid portion of the eye are quite similar. So, when a ray of light enters the eye it is refracted at the cornea. This refraction produce a real inverted and diminished image of distant objects on the retina. When the object is kept at different distances then we may expect the image to be formed at different distances from the lens. It means it may not form on the retina always. But in reality it is not so. Image is always formed on the retina. This is possible because the curvature of the crystalline lens is altered by ciliary muscles. When the eye is focused on infinity the muscles are relaxed and the eye lens remains thin. If the object is brought nearby the curvature increases so that the image can be formed on the retina. This property of the eye lens is called as accommodation. Then the question comes that how long does the image persist on the retina.

It is as long as the eye focuses the object or does it longer on after that also? It is very surprising to find that the image persists on the retina even after the object is removed. This is called 'the persistence of vision'. The persistence of vision is approximately one eight of a second. Even though human eye has the property of accommodation, the muscles cannot be strained beyond a limit and hence if the object is very close to the eye, clear image is not formed on the retina. Thus, there is a minimum distance for the clear vision of an object. This distance is called as 'least distance of distinct vision'. For a normal eye, this distance happens to be 25 cms. Organ Donation Frequently Asked Questions You are Here: Home Page > Organ and Tissue Donations > Organ Donation Frequently Asked Questions Organ Donation Frequently Asked Questions Versión en español 1. Why are organ, tissue and eye donations needed? There is a severe shortage of organs for life-saving transplants. In addition to those New Yorkers waiting for organ transplants, many more are helped by tissue donation such as skin for burn victims or eye donations for sight-restoring cornea transplants. Without these surgeries, they will die or remain disabled.

Transplants give people a chance to resume full, productive lives. 2. Who can become a donor? People of all ages may be able to become an organ, eye and tissue donor. Your medical condition at the time of death will decide what organs and tissues can be donated and/or used. Do not rule yourself out. 3. How do I sign up to be an organ, eye and tissue donor? You must be 18 years of age to sign up for the New York State Donate Life Registry. You can sign up when you obtain a driver license or non-driver identification (ID) card,or when you renew your driver license by signing the donor box that appears on each of these forms. Signing the back of your license does not enroll you in the New York State Donate Life Registry. You can also sign up through the New York State Health Department's web site, or on your voter registration form. 4. What happens when I join the Donate Life Registry? Signing up for the the New York State Donate Life Registry documents your gift, meaning that you are giving your legal consent to donate organs, eyes and tissues after death.

Registry information is kept private and can only be accessed for the purpose of identifying potential organ, eye and tissue donors at the time of death. Once you sign up, you will not need to carry a wallet card. Signing up for the registry is enough. 5. When I sign up, do I need to carry a wallet card to indicate my status as a donor? No, New York State does not issue donor wallet cards. Signing up in the New York State Donate Life Registry is enough. 6. I have already joined the New York State Life Pass it On Registry - should I sign up for the Donate Life Registry? What is the difference? To ensure that your decision to be an organ, tissue and eye donor is honored, you must sign up for the Donate Life Registry. If you joined the Life Pass it On intent registry, your name is not automatically switched to the Donate Life consent registry. The Life Pass It on Registry was created in 1999 and records someone's wish to be an organ and tissue donor. This is called an intent registry. Intent registries require next of kin's consent for donation to proceed in the event of the potential donor's death.

In 2006, a new law created the Donate Life Registry: a registry that records a person's own legal consent to organ, tissue and eye donation upon his or her death. If you are signed up in this new registry, your family will be informed of your decision and given information about the donation process, but their consent is not required to proceed with donation. 7. Do I have to tell my family about my decision to donate? It is strongly encouraged that you inform your family of your decision to donate. This may help when we tell your family of your decision. 8. How does the donation process begin? Hospitals are required to alert their federally designated organ procurement organization of all deaths. If you die outside of the hospital, your wish to donate may still be honored only if your family immediately notifies the coroner or funeral home. 9. If I join the Donate Life Registry, will medical care be compromised? No. Donation is only an option after all efforts to save the patient have failed and the patient has died. Saving the patient's life is the health care provider's main concern. 10. What will happen to my donated organs and tissues?

When someone dies, the local organ procurement organization, tissue bank or eye bank matches those donor's organs, eyes and tissues, as specified in the registry, with people waiting for transplants. Patients who receive your donation will be matched based upon many factors including: blood type, severity of illness and other medical criteria. Factors, such as race, gender, age and income are not considered when deciding who receives a transplant. 11. I am given the choice to donate for transplant and/or research. What does "research" mean? "Research" means making recovered organs, eyes and tissues that are not able to be transplanted offered to doctors and scientists to help cure diseases. If "transplantation and research" is selected, first priority is finding a suitable recipient before research is considered. 12. Is the registry used for whole body donation? No. Joining the New York State Donate Life Registry does not grant permission for your body to be donated to medical schools. Organ, eye and tissue donation for transplant or research is not the same as willed whole body donation. These Willed whole body programs are usually associated with teaching hospitals at major universities, and planning for this must be done in advance directly with the institutions.

Individuals can also contact the Association of Medical Schools of New York at 212-218-4610. 13. Can my body be donated for the study of science after donation of organs and tissue? Each medical school has its own guidelines about accepting body donations. Not all schools will accept body donations after organ, eye and/or tissue donation. If you are interested in willed whole body donation, check with the academic institutions you wish to support. They can answer specific questions about organ and tissue donation and pre-arrange the donation of your body for the advancement of science. 14. Can I specify who receives my donation? You are allowed to direct a donation to an individual by name. If the organ is a suitable match for a person who is waiting for a transplant, they can receive the transplant as a gift. You cannot restrict a donation on the basis of age, gender, race or ethnicity. 15. How can I make changes to my information or withdraw from the Donate Life Registry?

If you need to make changes to your information or you decide you do not want to become an organ, tissue and eye donor and you want your name taken off the Donate Life Registry, write to: The New York State Donate Life Registry New York State Department of Health 875 Central Avenue Albany, NY 12206. 16. I want the Donor Heart Symbol added to (or removed from) my DMV driver's license or ID How do I get a new one? In order to get the heart symbol added to or removed from your ID, you will need to order a new one. Please complete an MV-44 at the Department of Motor Vehicle (DMV). You can download this form or go to your local DMV office. 17. When must organs be recovered? Organs, eyes and tissues must be recovered as soon as possible after death. 18. If I donate my organs, eyes and tissues can I still have an open casket viewing? Donation does not affect the funeral arrangements or viewing. 19. Is there any cost to my estate or family for donating my organs, eyes and tissues No, there are no costs to your estate or family for you to be a donor. 20.

If I donate, does New York State take care of my remains? After the donation has taken place, families are responsible for funeral or burial arrangements. 21. What does my religion say about organ and tissue donation? All major religions approve of organ, eye and tissue donation and transplantation, and even encourage it. They believe it is the most significant gift one human being can give to another. If you have questions or concerns, you should discuss them with your religious or spiritual leader. For specific religious viewpoints, please visit . 22. If I am registered as a donor in New York, but die in another State, what happens? Hospitals in all states are required to alert their federally designated Organ Procurement Organization (OPO) of every death. Therefore, if one dies in another state, that state's OPO will contact the OPO of the person's home state to check if he or she has joined the Donate Life registry. If so, New York laws apply, but the donation will take place in the state in which the person has died. 23. Can I join more than one state registry?

Yes, anyone who spends a portion of time in New York State who would like to be an organ, eye and tissue donor should join the New York State Donate Life Registry, even if his or her home address is not in New York State. Questions or comments: donorreg@health.ny.gov What Organs Can Be Donated and Transplanted | organdonor.gov By registering as a cornea donor, you can also leave behind the gift of sight. Here are some facts about cornea and eye donation: Corneal transplants first performed: 1905 Corneal transplants performed in 2015: 48,792 The cornea is the clear part of the eye over the iris and pupil.

People may have damaged corneas from eye disease, injury, or birth defects A corneal transplant involves replacing a diseased or scarred cornea with a new one Since 1961, more than 1,000,000 men, women, and children ranging in age from nine days to 100+ years, have had their sight restored by corneal transplants More than 95% of all corneal transplants are successful in restoring the recipient’s vision Corneal donors don't have to "match" recipients like organ donors do. Donors are universal. Your blood type and eye color don't have to match. Age, eye color and how good your eyesight is, do not matter Most people can donate their corneas. Exceptions include people with infections or a few highly communicable diseases such as HIV or hepatitis Unlike organ donation, corneas can be recovered several hours after death and can be stored. A corneal transplant can be performed within 3-5 days after donation The white part of the eye is called the sclera, and that can be donated as well. The sclera can be used in operations to rebuild the eye.

Tissues Donated tissues save or dramatically improve the quality of life for the people who receive them. As an organ and tissue donor, you can enhance the lives of up to 50 people. Corneas, the middle ear, skin, heart valves, bone, veins, cartilage, tendons, and ligaments can be stored in tissue banks and used to restore sight, cover burns, repair hearts, replace veins, and mend damaged connective tissue and cartilage in recipients. Heart valves can be transplanted to save the lives of children born with heart defects, and adults with damaged heart valves. Skin can be used as a natural dressing for people with serious burns. It can even save lives by stopping infections. Bone is important for people receiving artificial joint replacements, or replacing bone that has been removed due to illness or injury, for example in hand and face transplants. Tendons, the elastic-like cords that attach bones and muscles to each other, can be donated to help rebuild damaged joints. Most people can be tissue donors when they die. The local tissue bank (a tissue recovery organization) will be notified by the hospital, medical examiner or funeral home. Tissue donation must be initiated within 24 hours of death.

However, tissue can be processed and stored for an extended period of time. Each year, about 30,000 donors provide lifesaving and life-enhancing tissue. Hands and Face Hands and faces have recently been added to the list of organs that can be successfully transplanted. These complicated surgeries are technically called vascularized composite allografts (VCAs) because they are surgeries composed of grafting many kinds of tissue: bone, muscle, nerves, skin, and blood vessels. In 2005, the first hand transplants were performed, and in 2007, the first face transplant was performed. Developments in immunosuppressive drugs help to keep these and all transplants from being rejected. Fewer than 125 hand and face transplants have been performed worldwide. But for the people who now have hands to use or a face to show the world, VCA transplants are transforming lives. Blood Stem Cells, Cord Blood, and Bone Marrow Healthy adults between the ages of 18 - 60 can donate blood stem cells.

In order for a blood stem cell transplant to be successful, the patient and the blood stem cell donor must have a closely matched tissue type or human leukocyte antigen (HLA). Since tissue types are inherited, patients are more likely to find a matched donor within their own family or racial/ethnic group. There are three sources of blood stem cells that healthy volunteers can donate: Bone marrow: This soft tissue is found in the interior cavities of bones. It is a major site of blood cell production and is removed to obtain stem cells. Cord blood stem cells: The umbilical cord that connected a newborn to the mother during pregnancy contains blood that has been shown to contain high levels of blood stem cells. Cord blood can be collected and stored in large freezers for a long period of time and, therefore, offers another source of stem cells available for transplanting into patients. Peripheral blood stem cells: The same types of stem cells found in marrow can be pushed out into a donor's bloodstream after the donor receives daily injections of a medication called filgrastim. This medication increases the number of stem cells circulating in the blood and provides a source of donor stem cells that can be collected in a way that is similar to blood donation.

If you are interested in donating blood stem cells, contact a donation organization . Blood and Platelets Blood and platelets are formed by the body, go through a life cycle, and are continuously replaced throughout life. This means that you can donate blood and platelets more than once. It is safe to donate blood every 56 days and platelets every four weeks. Blood is stored in a blood bank according to type (A, B, AB, or O) and Rh factor (positive or negative). Blood can be used whole, or separated into packed red cells, plasma, and platelets, all of which have different lifesaving uses. It takes only about 10 minutes to collect a unit (one pint) of blood, although with the testing and screening, the process of donating blood takes about an hour. Platelets are tiny cell fragments that circulate throughout the blood and aid in blood clotting. Platelets can be donated without donating blood. When a specific patient needs platelets, but does not need blood, a matching donor is found and platelets are separated from the rest of the blood which is returned to the donor. The donor's body will replace the missing platelets within a few hours.

Question: Which part of the human eye may be removed and kept in an eye bank?
Answer: THE CORNEA