What does lens mean? To become thinner towards the edges. Webster Dictionary(1.00 / 1 vote)Rate this definition: Lens(noun) a piece of glass, or other transparent substance, ground with two opposite regular surfaces, either both curved, or one curved and the other plane, and commonly used, either singly or combined, in optical instruments, for changing the direction of rays of light, and thus magnifying objects, or otherwise modifying vision. In practice, the curved surfaces are usually spherical, though rarely cylindrical, or of some other figure Origin: [L. lens a lentil. So named from the resemblance in shape of a double convex lens to the seed of a lentil. Cf. Lentil.] Freebase(3.00 / 1 vote)Rate this definition: Lens The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina.

This adjustment of the lens is known as accommodation. Accommodation is similar to the focusing of a photographic camera via movement of its lenses. The lens is more flat on its anterior side than on its posterior side. The lens is also known as the aquula or crystalline lens. In humans, the refractive power of the lens in its natural environment is approximately 18 dioptres, roughly one-third of the eye's total power. The Nuttall Encyclopedia(5.00 / 1 vote)Rate this definition: Lens a piece of glass adapted as convex or concave so as to change the direction of the rays of light passing through it and magnify or diminish the apparent size of an object. Numerology The numerical value of lens in Chaldean Numerology is: 7 Pythagorean Numerology CAN-C Cataract Eye Drops - IVP's Product Helping to reverse senile cataract The Aging Eye Growing old with Cataracts As our bodies age, change inevitably occurs. Stiff limbs, grey hair and wrinkles probably spring immediately to mind. Certainly we become stiffer and less agile and our bodies shrink and sag as they lose their youthful shapeliness as the years pass by.

Unfortunately the changes that age brings have a tendency to make our bodies much more vulnerable and prone to dysfunction. And our eyes are by no means the exception to prove the rule. For a start everybody's vision deteriorates with age independent of any aging eye diseases. One of the main reasons for this is that it is the pupil that determines how much light actually reaches the retina (the light sensitive layer of tissue at the back of the eye upon which images are focused on - it's the retina's job to then convert these images in to electric signals and to send them to the brain via the optic nerve). Unfortunately, the extent to which the pupil is able to dilate decreases with age and the inevitable consequence of this is that older eyes receive much less light at the retina. The statistics are pretty stark. The light adapted eye of a 20 year old receives six times more light than that of an 80 year old. In dark adapted conditions, the 20 year old eye receives about 16 times more light. In other words, for an older person, it's a like wearing medium-density sunglasses in bright light and extremely dark glasses in dim light.

For most of us, increasing age also brings with it the need to use reading glasses - even if you've never had to wear glasses before. This decline in vision is usually due to a condition known as presbyopia which refers to the eye's increasingly inability to focus on near objects. Although no-one really knows what the exact mechanisms at play are that result in presbyopia, research strongly points to it arising from a decline in the elasticity of lens. A loss of power in the muscles that bend and straighten the lens (the ciliary muscles) might also be responsible. Aging also brings with it a dramatic slowing in dark adaptation. Color vision changes cause a reduction in the ability to discriminate blues and blue-greens. The aging lens and cornea also cause glare by light scattering and aberrations of the cornea increase with age. All of this leads to poor vision especially when the pupil dilates in the dark. Perhaps the most irritating aspect of aging and the impact that it has on our vision as we grow older is the fact that our eyes just don't seem to work as well as they did when we were younger.

It all becomes a bit more of an effort, requiring us to concentrate harder and the need for higher levels of illumination just to reach the same perceptual levels as we did when we were young. And that's just the effect of the normal aging process quite apart from the age related diseases that can develop. We have, of course, already mentioned presbyopia but there are a number of other disease conditions that can affect the aging eye. And, although, here we are concentrating mainly on cataracts, it would be remiss to not at least mention these other conditions namely glaucoma, age-related macular degeneration (ARMD) and dry eye syndrome. Glaucoma is a condition that affects the optic nerve - the large nerve that carries electrical signals from the retina to the brain. The optic nerve is therefore crucial for vision - without it we could not see. If someone is suffering from glaucoma, their optic nerve is damaged and their ability to see becomes increasingly affected. At first peripheral vision is gradually destroyed, then central vision. If nothing is done total blindness will eventually result. The optic nerve damage that happens when someone is suffering from glaucoma usually results from higher than normal intraocular pressure (pressure within the eye itself).

Although incurable, it can be well managed by the use of eyedrops that effectively lower intraocular pressure. In fact there is evidence that Can-C eye-drops can help alleviate the intra ocular pressure associated with glaucoma. Inside the eye is the Schlemm canal which acts as a valve passing waste products out into the blood and also acting in its own right as a pressure valve too. Over time the canal gets somewhat blocked with cross-linked proteins, otherwise known as glycated end products, impaired materials that need to be disposed of. It is know that Can-C eye-drops help to prevent the formation of cross linked proteins and to aid their disposal. Thus from the anecdotal evidence of users who have seen reductions in their intra ocular eye-pressure, thus alleviating their glaucoma, it is assumed that Can-C is helping to literally unclog the Schell canal. Age -related macular degeneration is a condition that affects the central part of the retina known as the macula. Blood vessels under the retina leak blood and fluid, damaging retinal cells and causing blind spots in central vision.

Age related macular degeneration affects vision in the opposite way to glaucoma in that it is central vision that is affected first with peripheral vision being left intact. There are two types of age related macular degeneration known as wet and dry forms. The dry form is the early stage of the disease and will lead to the wet form in about 10% of cases which results in more severe vision loss. Age related macular degeneration is the most common cause of irreversible vision loss in the developed world. It is a very common condition. For example in the US approximately 11% of the US population aged 65 to 74 are affected by the condition. There has been a remarkable development and clinical evidence that a products known as MZS can help significantly reverse age-related macular degeneration. For more information about this please click here. Dry Eye Syndrome is an uncomfortable chronic condition that affects more women than men usually beginning in mid life. It is caused by a problem with tear production. We deal with this in more detail at (put in link here ...) But perhaps one of the most well known age related eye conditions is senile cataract.

A cataract is defined as a cloudiness or opacity within the lens of the eye. The lens itself is a transparent, biconvex structure that, along with the cornea, helps to refract light so that it focuses on the retina and provides us with a clear, sharp image. By changing shape, the lens is able to change the focal distance of the eye so that we are able to focus on objects at various distances. This process is known as accommodation. In a healthy eye the lens is transparent which allows light to pass easily through it. It is crucial for good vision and any loss of this transparency will produce less optimal vision. If the lens starts to become cloudy (in other word a cataract begins to develop) light does not pass easily through it and the result is that the image that reaches the retina becomes fuzzy and dull. The effect is a bit like looking through frosted glass or looking from behind a 'waterfall'. In fact, the literal meaning of the word 'cataract' is waterfall. It should be stressed that a cataract is not a 'new' growth in the lens.

Cataracts are defined as any cloudiness or opacity in the lens of the eye and the term 'cataract' simply means that the lens is not completely transparent any more. There are several different types of cataracts and they are generally classified by two different criteria - location in the lens and origin. When classified by location types of cataract include: Nuclear Sclerotic Cataract - This is the most common type of cataract that develops as a result of the aging process. A nuclear sclerotic cataract produces a gradual yellow cloudiness and hardening of the nucleus, or central portion, of the lens. The result is a gradual deterioration in vision Cortical Cataract - Whereas a nuclear sclerotic cataract is located in the central part of the lens, a cortical cataract clouds the periphery of the lens, called the cortex. Cortical cataracts generally look like wheel spokes which point inward towards the nucleus of the lens.

The effect of a cortical cataract is that light scatters when it hits the spokes Posterior Subcapsular Cataract - This type of cataract occurs on the back of the lens, below the capsular bag which encases the lens, typically starting near the center of the back part of the capsular bag. If you suffer from this type of cataract you are most likely to experience light sensitivity, blurry near vision, and glare and halos. Posterior subcapsular cataracts most commonly develop in people who suffer from diabetes or who have taken steroids for a prolonged time period Cataracts are also classified depending upon their origin i.e. the manner in which they develop. Classifications include: Age-Related Cataract - This is the most common type of cataract. Although senile cataracts can develop in your 40s and 50s they are far more likely to become an issue when you reach your 60s and 70s.

They are very common indeed and it is estimated that they affect around 60% of people over the age of 60 Secondary Cataract - This type of cataract develops secondary to some other problem - such as a result of undergoing eye surgery. Diabetics and steroid users are also prone to developing secondary cataracts Traumatic Cataract - A traumatic injury to the eye can result in cataracts developing. Such a cataract may not form immediately after the injury, but may develop years later Congenital Cataract - Although rare, some children are born with cataracts. This type of cataract is referred to as a congenital cataract Radiation Cataract - This type of cataract develops as a result of exposure to certain types of radiation, particularly ultraviolet light. Radiation cataracts are very rare It's clear then from looking at the above list that there are a number of risk factors that significantly increase your chances of developing cataracts. For example, being diabetic, using steroids, and having received an eye injury all increase your risk of suffering from cataracts.

Some risks are, of course, totally unavoidable - for example more women than men develop cataracts, as do people who suffer from myopia (short sightedness) and people with brown irises. Other risk factors such as smoking and sunlight exposure are within your control. But by far and above the greatest risk for developing cataracts is aging. Cataracts appear to develop as a result of changes in the arrangement of the proteins in the lens. Normally these are laid out in such a way that the lens is kept transparent but as we age, the protein structures can alter and opacities form as proteins start to clump together. The result is, of course, that some of the light entering the eye is no longer able to pass through the lens and reach the retina which leads to the distortion in vision. Unfortunately, no one really knows what causes these changes happen. However, it does appear to be part and parcel of the normal process of aging which is why cataracts are so common among the older population. At first the changes in the eye that lead to opacities developing may not be discernable.

Early cataracts are so microscopically small that although they do block a tiny amount of light it simply doesn't affect what you are seeing. And as cataracts do not cause pain or redness you may not realize that you have a problem. In fact cataracts can begin many years before they actually affect your vision although for some people they develop more quickly. Cataracts also usually form in both eyes but may develop more quickly in one eye than the other. Gradually though your vision will be affected as it becomes increasingly blurry. Glare in low-light conditions can also be problematic which can particularly affect your ability to drive at night. You may also experience other problems such as reduced color vision. Remarkably some people actually experience an initial improvement in their vision (a phenomena known as second sight) although this is only temporary and gradually vision will deteriorate. Once your cataracts have been diagnosed and the issues with your vision are becoming problematic, your ophthalmologist will probably advise you that you require surgery as the only way to treat your condition. But surgery is now no longer the only option available to you. Thanks to remarkable developments in the treatment of cataracts, Can-C Eye drops now offer a ground breaking alternative to surgery.

For the first time cataracts can be treated simply by the daily use of eye drops. Specifically designed of the treatment of senile cataracts and using a unique, patented formula containing the active ingredient N-acetylcarnosine, Can-C Eye drops gently but effectively halt and can even reverse the progress of cataracts. And the results are evident incredibly quickly. Even after just 1 month of treatment, the effects of Can-C carnosine eye drops are clearly visible - breaking down the damaged proteins that cause the cataracts. What's more, by combining the use of Can-C Eyedrops with Can-C Plus capsules you can make your treatment regime even more effective. Can-C Plus is a nutritional supplement that actively improves the environment in the eye, making it even more receptive to Can-C Eyedrops. So even though growing old is unavoidable and brings with it increased risks of developing cataracts, Can-C Eyedrops at last mean that surgery is no longer the inevitable conclusion you must reach.

By allowing you to take control of your condition, you can now turn back the hands of time and what was once thought of as just being part and parcel of growing old, can now be treated gently and effectively, without the need for any invasive procedures at all. World Of Optometry: Human Lens A simple blog which will have useful links related to Optometry & Ophthalmology. Sunday, December 5, 2010 Human Lens The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refractlight to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation . It is similar to the focusing of a photographic camera via movement of its lenses. The lens is flatter on its anterior side.The lens is also known as the aquula (Latin, a little stream, dim. of aqua, water) or crystalline lens.

In humans, the refractive power of the lens in its natural environment is approximately 18 dioptres, roughly one-third of the eye's total power. Position, size, and shape The lens is part of the anterior segment of the eye. Anterior to the lens is the iris, which regulates the amount of light entering into the eye. The lens is suspended in place by the zonular fibers, which attach to the lens near its equatorial line and connect the lens to the ciliary body. Posterior to the lens is the vitreous body, which, along with the aqueous humor on the anterior surface, bathes the lens. The lens has an ellipsoid, biconvex shape. The anterior surface is less curved than the posterior. In the adult, the lens is typically circa 10 mm in diameter and has an axial length of about 4 mm, though it is important to note that the size and shape can change due to accommodation and because the lens continues to grow throughout a person’s lifetime Variations among vertebrates In many aquatic vertebrates, the lens is considerably thicker, almost spherical, to increase the refraction of light.

This difference compensates for the smaller angle of refraction between the eye's cornea and the watery medium, as they have similar refractive indices. Even among terrestrial animals, however, the lens of primates such as humans is unusually flat. In reptiles and birds, the ciliary body touches the lens with a number of pads on its inner surface, in addition to the zonular fibres. These pads compress and release the lens to modify its shape while focusing on objects at different distances; the zonular fibres perform this function inmammals. In fish and amphibians, the lens is fixed in shape, and focussing is instead achieved by moving the lens forwards or backwards within the eye. In cartilaginous fish the zonular fibres are replaced by a membrane, including a small muscle at the underside of the lens. This muscle pulls the lens forward from its relaxed position when focusing on nearby objects. In teleosts, by contrast, a muscle projects from a vascular structure in the floor of the eye, called the falciform process, and serves to pull the lens backwards from the relaxed position to focus on distant objects.

While amphibians move the lens forward, as do cartilaginous fish, the muscles involved are not homologous with those of either type of fish. In frogs, there are two muscles, one above and one below the lens, while other amphibians have only the lower muscle. In the most primitive vertebrates, the lampreys and hagfish, the lens is not attached to the outer surface of the eyeball at all. There is no aqueous humour in these fish, and the vitreous body simply presses the lens against the surface of the cornea. To focus its eyes, a lamprey flattens the cornea using muscles outside of the eye, and pushes the lens backwards. Lens structure and function The lens has three main parts: the lens capsule, the lens epithelium, and the lens fibers. The lens capsule forms the outermost layer of the lens and the lens fibers form the bulk of the interior of the lens. The cells of the lens epithelium, located between the lens capsule and the outermost layer of lens fibers, are found only on the anterior side of the lens. Lens capsule The lens capsule is a smooth, transparent basement membrane that completely surrounds the lens.

The capsule is elastic and is composed of collagen. It is synthesized by the lens epithelium and its main components are Type IV collagen and sulfated glycosaminoglycans (GAGs). The capsule is very elastic and so causes the lens to assume a more globular shape when not under the tension of the zonular fibers, which connect the lens capsule to the ciliary body. The capsule varies from 2-28 micrometres in thickness, being thickest near the equator and thinnest near the posterior pole. The lens capsule may be involved with the higher anterior curvature than posterior of the lens. Lens epithelium The lens epithelium, located in the anterior portion of the lens between the lens capsule and the lens fibers, is a simple cuboidal epithelium. The cells of the lens epithelium regulate most of the homeostatic functions of the lens. As ions, nutrients, and liquid enter the lens from the aqueous humor, Na+/K+ ATPase pumps in the lens epithelial cells pump ions out of the lens to maintain appropriate lens osmolarity and volume, with equatorially positioned lens epithelium cells contributing most to this current.

The activity of the Na+/K+ ATPases keeps water and current flowing through the lens from the poles and exiting through the equatorial regions. The cells of the lens epithelium also serve as the progenitors for new lens fibers. It constantly lays down fibers in the embryo, fetus, infant, and adult, and continues to lay down fibers for lifelong growth. Lens fibers The lens fibers form the bulk of the lens. They are long, thin, transparent cells, firmly packed, with diameters typically between 4-7 micrometres and lengths of up to 12 mm long.The lens fibers stretch lengthwise from the posterior to the anterior poles and, when cut horizontally, are arranged in concentric layers rather like the layers of an onion. If cut along the equator, it appears as a honeycomb. The middle of each fiber lies on the equator. These tightly packed layers of lens fibers are referred to as laminae. The lens fibers are linked together via gap junctions and interdigitations of the cells that resemble “ball and socket” forms. The lens is split into regions depending on the age of the lens fibers of a particular layer.

Moving outwards from the central, oldest layer, the lens is split into an embryonic nucleus, the fetal nucleus, the adult nucleus, and the outer cortex. New lens fibers, generated from the lens epithelium, are added to the outer cortex. Mature lens fibers have no organelles or nuclei. Accommodation: changing the power of the lens An image that is partially in focus, but mostly out of focus in varying degrees. The lens is flexible and its curvature is controlled by ciliary muscles through the zonules. By changing the curvature of the lens, one can focus the eye on objects at different distances from it. This process is called accommodation. At short focal distance the ciliary muscle contracts, zonule fibers loosen, and the lens thickens, resulting in a rounder shape and thus high refractive power. Changing focus to an object at a greater distance requires the relaxation of the ciliary muscle, which in turn increases the tension on the zonules, flattening the lens and thus increasing the focal distance. The refractive index of the lens varies from approximately 1.406 in the central layers down to 1.386 in less dense cortex of the lens.

This index gradient enhances the optical power of the lens. Aquatic animals must rely entirely on their lens for both focusing and to provide almost the entire refractive power of the eye as the water-cornea interface does not have a large enough difference in indices of refraction to provide significant refractive power. As such, lenses in aquatic eyes tend to be much rounder and harder. Crystallins and transparency Crystallins are water-soluble proteins that compose over 90% of the protein within the lens. The three main crystallin types found in the human eye are α-, β-, and γ-crystallins. Crystallins tend to form soluble, high-molecular weight aggregates that pack tightly in lens fibers, thus increasing the index of refraction of the lens while maintaining its transparency. β and γ crystallins are found primarily in the lens, while subunits of α -crystallin have been isolated from other parts of the eye and the body. α-crystallin proteins belong to a larger superfamily of molecular chaperone proteins, and so it is believed that the crystallin proteins were evolutionarily recruited from chaperone proteins for optical purposes.

The chaperone functions of α -crystallin may also help maintain the lens proteins, which must last a human for his/her entire lifetime. Another important factor in maintaining the transparency of the lens is the absence of light-scattering organelles such as the nucleus,endoplasmic reticulum, and mitochondria within the mature lens fibers. Lens fibers also have a very extensive cytoskeleton that maintains the precise shape and packing of the lens fibers; disruptions/mutations in certain cytoskeletal elements can lead to the loss of transparency. Development and growth Development of the human lens begins at the 4 mm embryonic stage. Unlike the rest of the eye, which is derived mostly from the neural ectoderm, the lens is derived from the surface ectoderm. The first stage of lens differentiation takes place when the optic vesicle, which is formed from outpocketings in the neural ectoderm, comes in proximity to the surface ectoderm. The optic vesicle induces nearby surface ectoderm to form thelens placode. At the 4 mm stage, the lens placode is a single monolayer of columnar cells. As development progresses, the lens placode begins to deepen and invaginate.

As the placode continues to deepen, the opening to the surface ectoderm constricts and the lens cells forms a structure known as the lens vesicle. By the 10 mm stage, the lens vesicle has completely separated from the surface ectoderm. After the 10 mm stage, signals from the developing neural retina induces the cells closest to the posterior end of the lens vesicle begin to elongate toward the anterior end of the vesicle. These signals also induce the synthesis of crystallins. These elongating cells eventually fill in the lumen of the vesicle to form the primary fibers, which become the embryonic nucleus in the mature lens. The cells of the anterior portion of the lens vesicle give rise to the lens epithelium. Additional secondary fibers are derived from lens epithelial cells located toward the equatorial region of the lens. These cells lengthen anteriorly and posteriorly to encircle the primary fibers. The new fibers grow longer than those of the primary layer, but as the lens gets larger, the ends of the newer fibers cannot reach the posterior or anterior poles of the lens. The lens fibers that do not reach the poles form tight, interdigitating seams with neighboring fibers.

These seams are readily visible and are termed sutures. The suture patterns become more complex as more layers of lens fibers are added to the outer portion of the lens. The lens continues to grow after birth, with the new secondary fibers being added as outer layers. New lens fibers are generated from the equatorial cells of the lens epithelium, in a region referred to as the germinative zone. The lens epithelial cells elongate, lose contact with the capsule and epithelium, synthesize crystallin, and then finally lose their nuclei (enucleate) as they become mature lens fibers.From development through early adulthood, the addition of secondary lens fibers results in the lens growing more ellipsoid in shape; after about age 20, however, the lens grows rounder with time. Nourishment The lens is metabolically active and requires nourishment in order to maintain its growth and transparency. Compared to other tissues in the eye, however, the lens has considerably lower energy demands. By nine weeks into human development, the lens is surrounded and nourished by a net of vessels, the tunica vasculosa lentis, which is derived from the hyaloid artery.

Beginning in the fourth month of development, the hyaloid artery and its related vasculature begin to atrophy and completely disappear by birth. In the postnatal eye, Cloquet’s canal marks the former location of the hyaloid artery. After regression of the hyaloid artery, the lens receives all its nourishment from the aqueous humor. Nutrients diffuse in and waste diffuses out through a constant flow of fluid from the anterior/posterior poles of the lens and out of the equatorial regions, a dynamic that is maintained by theNa+/K+ ATPase pumps located in the equatorially positioned cells of the lens epithelium. Glucose is the primary energy source for the lens. As mature lens fibers do not have mitochondria, approximately 80% of the glucose is metabolized via anaerobic respiration. The remaining fraction of glucose is shunted primarily down the pentose phosphate pathway. The lack of aerobic respiration means that the lens consumes very little oxygen as well. at Function Of Lens In Eye - YouTube Function Of Lens In Eye Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content.

Rating is available when the video has been rented. This feature is not available right now. Please try again later. Published on May 11, 2015 Function Of Lens In Eye. . .Lens Anatomy, Definition & Function | Body Maps - Healthline The lens is located in the eye. By changing its shape, the lens changes the focal distance of the eye. In other words, it focuses the light rays that pass through it ... Lens (anatomy) - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Lens_(anatomy) The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. ‎Structure - ‎Function - ‎Clinical significance - ‎Additional images Lens of the Eye: Definition & Function | Study.com study.com/academy/lesson/lens-of-the-eye-definition-function.html The lens of the eye focuses light and allows you to see. In this lesson, you will learn what the lens is made of and how it changes shape so that... The Eye - how it works and anatomy : University of Michigan ...

› Patient Care › Eye Conditions Mar 12, 2014 - How the eye works and descriptions and functions of the major structures of the human eye: Choroid, Cornea, Fovea , Iris , Macula , Lens, Optic ... Crystalline lens | eyepedia Function. The crystalline lens is suspended within the eye behind the coloured iris. It acts to fine-tune the focusing of the eye to form a picture of the world on the ... lens | eye structure | Encyclopedia Britannica Mar 25, 2014 - lens, in anatomy, a nearly transparent biconvex structure suspended behind the iris of the eye, the sole function of which is to focus light rays ... Category Ophthalmology Terms Doctor Portal Ophthalmology Terms Amsler Grid — a grid of horizontal and vertical lines used to monitor a person's central visual field. The grid was developed by Marc Amsler, a Swiss ophthalmologist. It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration, Epiretinal membrane), as well as the optic nerve and the visual pathway to the brain.

Choroid — Sandwiched between the retina and the sclera is a tissue abundant in blood vessels, called the choroids. Cornea — The transparent front part of the eye that covers the iris, pupil, and anterior chamber. Cryotherapy — Is the application of extreme cold to destroy abnormal or diseased tissue. Its goal is to decrease cellular metabolism, increase cellular survival, decrease inflammation, decrease pain and spasm, promote vasoconstriction, and to destroy cells by crystallizing the cytosol. Edema — An abnormal accumulation of fluid which causes swelling. Eye lens — A transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, the lens functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp image of the object of interest to be formed on the retina. Enucleation — Is the surgical removal of the eye. Fluorescein angiogram — A more complex photographic technique, permits additional views of the retina when a special vegetable-based dye is injected into a vein your arm. This is not an X-ray and the dye contains no iodine.

All of our offices are equipped with dark room facilities and digital image computers to process your films and when necessary results can be obtained at the time of your initial visit. Fundus photographs — Provide a view of the interior of the eye, including the retina and macula, and are taken by a special camera attached to a low power microscope. Iris — A thin, circular structure in the eye responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. Kenalog — or Triamcinolone is a long-acting synthetic corticosteroid given orally, by injection, inhalation, or as a topical ointment or cream to reduce inflammation. Lucentis/Avastin — Drugs that block angiogenesis, the growth of new blood vessels. Many diseases of the eye, such as age-related macular degeneration (AMD) and diabetic retinopathy, damage the retina and cause blindness when blood vessels around the retina grow abnormally and leak fluid, causing the layers of the retina to separate. This abnormal growth is caused by vascular endothelial growth factor (VEGF is a protein that stimulates blood vessel growth). Lucentis and Avastin have been successfully used to inhibit VEGF and slow this growth.

Macula — The central area of the retina is called the macula. The macula is responsible for sharp, central vision. Good central vision is critical for activities such as reading, driving, and sewing. If the macula is damaged by disease, the "straight ahead" vision is affected. The rest of the retina is responsible for peripheral vision. Optic nerve — Also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection. Retina — In a manner similar to a camera, light enters the front of your eye through the cornea and lens and is brought to focus on the back of your eye on the tissue called the retina. In a sense, the retina functions like the film in a camera. From there, the signals are transmitted to the brain, thereby creating sight. Sclera — Also known as the white or white of the eye, is the opaque, fibrous, protective, outer layer of the eye containing collagen and elastic fiber.

Ultrasound — Procedure which records sound waves reflected from the tissues of the eye creates a video image to permit the doctors to see inside the eye and to make special measurements. Vitreous — The clear gel that fills the central cavity of the eye. How the eye focuses light | Sciencelearn Hub How the eye focuses light How the eye focuses light How the eye focuses light Video: How the eye works The eye is structurally designed to detect and process light. The cornea and the crystalline lens are both important for the eye to focus light. The eye focuses light in a similar way to when you use a magnifying glass to concentrate the Sun’s rays onto a piece of paper. The distance from the magnifying lens to the piece of paper is the focal length . For the eye, light from distant objects is focused onto the retina at the back of the eye. The eye is about the size of a table tennis ball, so the focal length needs to be about 2.5 cm. The cornea does most of the focusing Video: The eye’s lens system About 70% of the bending of light takes place as it enters the cornea and the aqueous fluid.

This bending is possible because of the curve of the cornea as well as the change in refractive index as light moves from air into the cornea and then into the aqueous fluid between the cornea and the iris. Air has a refractive index of 1.00, and the aqueous fluid behind the cornea has a refractive index of 1.33. If the change in refractive index was not as great, the light would not bend as much. This becomes noticeable if you try to look at something when you are under water. Things appear out of focus because the cornea is designed to work with light passing into it from air rather than from water. Wearing swimming goggles under water allows the layer of air to be present. The crystalline lens and accommodation Behind the aqueous fluid is the second lens system. It consists of a convex lens that is soft and pliable. The ciliary muscle is a circular ring of muscle that attaches all the way around the lens. This ciliary muscle can change the shape of the crystalline lens by stretching it at the edges. It is attached to the lens by zonules (ligament fibres that can be tight or loose).

When you are looking at a near object, the lens needs to become more rounded at the central surface in order to focus the light rays. This ability to change focus for close-up objects is called accommodation . Two totally opposite theories for accommodation There are two main theories for how the lens changes shape. Helmholtz theory – proposed in 1855. When the ciliary muscle contracts, all zonular tension is reduced. This permits the central lens surface lens to become rounder (increases its focusing power). When the ciliary muscle relaxes, all zonular tension is increased, causing the lens to flatten (decrease in optical power). Schachar mechanism – proposed in 1992. When the ciliary muscle contracts, equatorial zonular tension is increased. This causes the central lens surface to become more steeply rounded (increases central optical power). When the ciliary muscle relaxes, equatorial zonular tension is reduced, causing the central lens surface to flatten (decrease in optical power). Image: Theories of eye accommodation The Schachar mechanism can be demonstrated using a Mylar balloon (a shiny silver flat balloon that is often used with helium ).

If you look at your reflected image on the flat side of the balloon, you will notice that it becomes smaller if you pull the edges of the balloon outwards. This is because the centre of the balloon becomes more convex. Loss of accommodation Video: Presbyopia – the old eye As we age, the ability of the ciliary muscle to change the shape of the crystalline lens lessens. For most people, their ability to focus on close-up images decreases, but distance vision is unaffected. This is known as presbyopia and is one reason that older people often need reading glasses. According to the Helmholtz theory, the lens becomes harder as people age. This means that the ciliary muscle is no longer able to sufficiently change the shape of the lens. According to the Schachar theory, the lens does not lose any of its flexibility with age. Rather, a loss of accommodation is caused because the lens continues to grow slightly with age. This increase in size means that the distance between the lens and the ciliary muscle decreases, which means that the ciliary muscle is not able to provide the same tension to the edges of the lens.

Nature of science When an alternative proposal of how something works is suggested, there is often a long process of discussion and experiment before the new idea is either disregarded or accepted. For example, since Dr Schachar proposed an alternative mechanism of how the ciliary muscles change the shape of the lens, there has been much argument and counter-argument. After nearly 20 years, the debate is still on-going. Useful links Learn more about the Schachar mechanism of how the ciliary muscles and zonular fibres change the shape of the lens. Bifocal lens | definition of bifocal lens by Medical dictionary Bifocal lens | definition of bifocal lens by Medical dictionary Related to bifocal lens: Progressive lens lens [lenz] 1. a piece of glass or other transparent material so shaped as to converge or scatter light rays. See also glasses . 2. the transparent, biconvex body separating the posterior chamber and the vitreous body of the eye; it refracts (bends) light rays so that they are focused on the retina . Called also crystalline lens .

In order for the eye to see objects close at hand, light rays from the objects must be bent more sharply to bring them to focus on the retina; light rays from distant objects require much less refraction . It is the function of the lens to do accommodation , making of adjustments for viewing both near objects and more distant ones. To accomplish this it must be highly elastic so that its shape can be changed and made more or less convex . The more convex the lens, the greater the refraction . Small ciliary muscles create tension on the lens, making it less convex; as the tension is relaxed the lens becomes more spherical in shape and hence more convex. With increasing age the lenses lose their elasticity; thus their ability to focus light rays in the retina becomes impaired. This condition is called presbyopia . In farsightedness ( hyperopia ) the image is focused behind the retina because the refractive power of the lens is too weak or the eyeball axis is too short. Nearsightedness ( myopia ) occurs when the refractive power of the lens is too strong or the eyeball is too long, so that the image is focused in front of the retina. The biconvex lens of the eye.

From Frazier et al., 1996. achromatic lens one corrected for chromatic (color) aberration. apochromatic lens one corrected for chromatic (color) and spheric aberration. biconcave lens one concave on both faces. biconvex lens one convex on both faces. bifocal lens one having two segments with different refracting power, the upper for far vision and the lower for near vision. See also bifocal glasses . concave lens one curved like a section of the interior of a hollow sphere; it disperses light rays. Called also diverging lens . contact l's corrective lenses that fit directly over the cornea of the eye; see also contact lenses. converging lens (convex lens) one curved like the exterior of a hollow sphere; it brings light to a focus. convexoconcave lens one that has one convex and one concave face. crystalline lens lens (def. 2). cylindrical lens one with at least one nonspherical surface, used to correct astigmatism .

Question: What transparent, biconvex structure changes shape to change the focal distance of the eye so that it can focus on objects at different distances?
Answer: Lens