# Ophthalmology

Ophthalmology (/ˌɒfθælˈmɒlədʒi/, OFF-thal-MOL-ə-jee) is a clinical and surgical specialty within medicine that deals with the diagnosis and treatment of eye disorders. A former term is oculism.
An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a medical degree, a doctor specialising in ophthalmology must pursue additional postgraduate residency training specific to that field. This may include a one-year integrated internship that involves more general medical training in other fields such as internal medicine or general surgery. Following residency, additional specialty training (or fellowship) may be sought in a particular aspect of eye pathology.
Ophthalmologists prescribe medications to treat ailments, such as eye diseases, implement laser therapy, and perform surgery when needed. Ophthalmologists provide both primary and specialty eye care—medical and surgical. Most ophthalmologists participate in academic research on eye diseases at some point in their training and many include research as part of their career. Ophthalmology has always been at the forefront of medical research with a long history of advancement and innovation in eye care.

## Diseases

A brief list of some of the most common diseases treated by ophthalmologists:
* Cataract
* Excessive tearing (tear duct obstruction)
* Proptosis (bulged eyes)
* Thyroid eye disease
* Eye tumors
* Ptosis
* Diabetic retinopathy
* Dry eye syndrome
* Glaucoma
* Macular degeneration
* Retinal detachment
* Endophthalmitis
* Refractive errors
* Strabismus (misalignment or deviation of eyes)
* Uveitis
* Ocular trauma
* Ruptured globe injury
* Orbital fracture
The most valued pharmaceutical companies worldwide whose leading products are in Ophthalmology are Regeneron (United States) for Macular degeneration (AMD) treatment and Bausch Health (Canada) for Front of eye.

## Diagnosis
### Eye examination

Following are examples of examination methods performed during an eye examination that enables diagnosis
* Visual acuity assessment
* Ocular tonometry to determine intraocular pressure
* Extraocular motility and ocular alignment assessment
* Slit lamp examination
* Dilated fundus examination
* Gonioscopy
* Refraction

### Specialized tests

Optical coherence tomography (OCT) is a medical technological platform used to assess ocular structures. The information is then used by physicians to assess staging of pathological processes and confirm clinical diagnoses. Subsequent OCT scans are used to assess the efficacy of managing diabetic retinopathy, age-related macular degeneration, and glaucoma.
Optical coherence tomography angiography (OCTA) and Fluorescein angiography to visualize the vascular networks of the retina and choroid.
Electroretinography (ERG) measures the electrical responses of various cell types in the retina, including the photoreceptors (rods and cones), inner retinal cells (bipolar and amacrine cells), and the ganglion cells.
Electrooculography (EOG) is a technique for measuring the corneo-retinal standing potential that exists between the front and the back of the human eye. The resulting signal is called the electrooculogram. Primary applications are in ophthalmological diagnosis and in recording eye movements.
Visual field testing to detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits.
Corneal topography is a non-invasive medical imaging technique for mapping the anterior curvature of the cornea, the outer structure of the eye.
Ultrasonography of the eyes may be performed by an ophthalmologist.

## Ophthalmic surgery

Eye surgery, also known as ocular surgery, is surgery performed on the eye or its adnexa by an ophthalmologist. The eye is a fragile organ, and requires extreme care before, during, and after a surgical procedure. An eye surgeon is responsible for selecting the appropriate surgical procedure for the patient and for taking the necessary safety precautions.

## Subspecialties

Ophthalmology includes subspecialities that deal either with certain diseases or diseases of certain parts of the eye. Some of them are:
* Anterior segment surgery
* Cornea, ocular surface, and external disease
* Glaucoma
* Neuro-ophthalmology
* Ocular oncology
* Oculoplastics and orbit surgery
* Ophthalmic pathology
* Paediatric ophthalmology/strabismus (misalignment of the eyes)
* Refractive surgery
* Medical retina, deals with treatment of retinal problems through non-surgical means
* Uveitis
* Veterinary specialty training programs in veterinary ophthalmology exist in some countries.
* Vitreo-retinal surgery, deals with surgical management of retinal and posterior segment diseases
Medical retina and vitreo-retinal surgery sometimes are combined and together they are called posterior segment subspecialisation

## Etymology

The Greek roots of the word ophthalmology are ὀφθαλμός (ophthalmos, "eye") and -λoγία (-logia, "study, discourse"), i.e., "the study of eyes". The discipline applies to all animal eyes, whether human or not, since the practice and procedures are quite similar with respect to disease processes, although there are differences in the anatomy or disease prevalence.

## History
### Ancient near east and the Greek period

In the Ebers Papyrus from ancient Egypt dating to 1550 BC, a section is devoted to eye diseases.
Prior to Hippocrates, physicians largely based their anatomical conceptions of the eye on speculation, rather than empiricism. They recognized the sclera and transparent cornea running flushly as the outer coating of the eye, with an inner layer with pupil, and a fluid at the centre. It was believed, by Alcamaeon (fifth century BC) and others, that this fluid was the medium of vision and flowed from the eye to the brain by a tube. Aristotle advanced such ideas with empiricism. He dissected the eyes of animals, and discovering three layers (not two), found that the fluid was of a constant consistency with the lens forming (or congealing) after death, and the surrounding layers were seen to be juxtaposed. He and his contemporaries further put forth the existence of three tubes leading from the eye, not one. One tube from each eye met within the skull.
The Greek physician Rufus of Ephesus (first century AD) recognised a more modern concept of the eye, with conjunctiva, extending as a fourth epithelial layer over the eye. Rufus was the first to recognise a two-chambered eye, with one chamber from cornea to lens (filled with water), the other from lens to retina (filled with a substance resembling egg whites).
Celsus the Greek philosopher of the second century AD gave a detailed description of cataract surgery by the couching method.
The Greek physician Galen (second century AD) remedied some mistaken descriptions, including about the curvature of the cornea and lens, the nature of the optic nerve, and the existence of a posterior chamber. Although this model was a roughly correct modern model of the eye, it contained errors. Still, it was not advanced upon again until after Vesalius. A ciliary body was then discovered and the sclera, retina, choroid, and cornea were seen to meet at the same point. The two chambers were seen to hold the same fluid, as well as the lens being attached to the choroid. Galen continued the notion of a central canal, but he dissected the optic nerve and saw that it was solid. He mistakenly counted seven optical muscles, one too many. He also knew of the tear ducts.

### Ancient India

The Indian surgeon Sushruta wrote the Sushruta Samhita in Sanskrit in approximately the sixth century BC, which describes 76 ocular diseases (of these, 51 surgical) as well as several ophthalmological surgical instruments and techniques. His description of cataract surgery was compatible with the method of couching. He has been described as one of the first cataract surgeons.

### Medieval Islam

Medieval Islamic Arabic and Persian scientists (unlike their classical predecessors) considered it normal to combine theory and practice, including the crafting of precise instruments, and therefore, found it natural to combine the study of the eye with the practical application of that knowledge. Hunayn ibn Ishaq, and others beginning with the medieval Arabic period, taught that the crystalline lens is in the exact center of the eye. This idea was propagated until the end of the 1500s.
Ibn al-Nafis, an Arabic native of Damascus, wrote a large textbook, The Polished Book on Experimental Ophthalmology, divided into two parts, On the Theory of Ophthalmology and Simple and Compounded Ophthalmic Drugs.
Avicenna wrote in his Canon "rescheth", which means "retiformis", and Gerard of Cremona translated this at approximately 1150 into the new term "retina".

### Modern period

In the seventeenth and eighteenth centuries, hand lenses were used by Malpighi, microscopes by Leeuwenhoek, preparations for fixing the eye for study by Ruysch, and later the freezing of the eye by Petit. This allowed for detailed study of the eye and an advanced model. Some mistakes persisted, such as: why the pupil changed size (seen to be vessels of the iris filling with blood), the existence of the posterior chamber, and the nature of the retina. Unaware of their functions, Leeuwenhoek noted the existence of photoreceptors, however, they were not properly described until Gottfried Reinhold Treviranus in 1834.
Jacques Daviel performed the first documented planned primary cataract extraction on Sep. 18, 1750 in Cologne. Georg Joseph Beer (1763–1821) was an Austrian ophthalmologist and leader of the First Viennese School of Medicine. He introduced a flap operation for treatment of cataract (Beer's operation), as well as having popularized the instrument used to perform the surgery (Beer's knife).
In North America, indigenous healers treated some eye diseases by rubbing or scraping the eyes or eyelids.

### Ophthalmic surgery in The United Kingdom

The first ophthalmic surgeon in the UK was John Freke, appointed to the position by the governors of St. Bartholomew's Hospital in 1727. A major breakthrough came with the appointment of Baron de Wenzel (1724–90), a German who became the oculist to King George III of Great Britain in 1772. His skill at removing cataracts legitimized the field. The first dedicated ophthalmic hospital opened in 1805 in London; it is now called Moorfields Eye Hospital. Clinical developments at Moorfields and the founding of the Institute of Ophthalmology (now part of the University College London) by Sir Stewart Duke-Elder established the site as the largest eye hospital in the world and a nexus for ophthalmic research.

### Central Europe

In Berlin, ophthalmologist Albrecht von Graefe introduced iridectomy as a treatment for glaucoma and improved cataract surgery, he is also considered the founding father of the German Ophthalmological Society.
Numerous ophthalmologists fled Germany after 1933 as the Nazis began to persecute those of Jewish descent. A representative leader was Joseph Igersheimer (1879–1965), best known for his discoveries with arsphenamine for the treatment of syphilis. He fled to Turkey in 1933. As one of eight emigrant directors in the Faculty of Medicine at the University of Istanbul, he built a modern clinic and trained students. In 1939, he went to the United States, becoming a professor at Tufts University. German ophthalmologist, Gerhard Meyer-Schwickerath is widely credited with developing the predecessor of laser coagulation, photocoagulation.
In 1946, Igersheimer conducted the first experiments on light coagulation. In 1949, he performed the first successful treatment of a retinal detachment with a light beam (light coagulation) with a self-constructed device on the roof of the ophthalmic clinic at the University of Hamburg-Eppendorf.
Polish ophthalmology dates to the thirteenth century. The Polish Ophthalmological Society was founded in 1911. A representative leader was Adam Zamenhof (1888–1940), who introduced certain diagnostic, surgical, and nonsurgical eye-care procedures. He was executed by the German Nazis in 1940.
Zofia Falkowska (1915–93) head of the Faculty and Clinic of Ophthalmology in Warsaw from 1963 to 1976, was the first to use lasers in her practice.

### Contributions by physicists

The prominent physicists of the late nineteenth and early twentieth centuries included Ernst Abbe (1840–1905), a co-owner of at the Zeiss Jena factories in Germany, where he developed numerous optical instruments. Hermann von Helmholtz (1821–1894) was a polymath who made contributions to many fields of science and invented the ophthalmoscope in 1851. They both made theoretical calculations on image formation in optical systems and also had studied the optics of the eye.