Ophthalmology is the branch of medicine which deals with the diseases and surgery of the visual pathways, including the eye, brain, and areas surrounding the eye, such as the lacrimal system and eyelids. The word ophthalmology comes from the Greek roots ophthalmos meaning eye and logos meaning word, thought or discourse; ophthalmology literally means "The science of eyes." As a discipline it applies to animal eyes also, since the differences from human practice are surprisingly minor and are related mainly to differences in anatomy or prevalence, not differences in disease processes. However, veterinary medicine is regulated separately in many countries and states/provinces resulting in few ophthalmologists treating both humans and animals. By convention the term ophthalmologist is more restricted and implies a medically trained specialist. Since ophthalmologists perform operations on eyes, they are generally categorized as surgeons.

History of ophthalmology
Sushruta wrote Sushruta Samhita in about fifth Century BCE in India. He described about 72 ocular diseases as well as several ophthalmological surgical instruments and techniques. Sushruta has been described as the first Indian cataract surgeon. [1] [2] [3] Arab scientists are some of the earliest to have written about and drawn the anatomy of the eye—the earliest known diagram being in Hunain ibn Is-hâq's Book of the Ten Treatises on the Eye. Earlier manuscripts exist which refer to diagrams which are not known to have survived. Current knowledge of the Græco-Roman understanding of the eye is limited, as many manuscripts lacked diagrams. In fact, there are very few Græco-Roman diagrams of the eye still in existence. Thus, it is not clear to which structures the texts refer, and what purpose they were thought to have.

Sushruta
The pre-Hippocratics 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 and others, that this fluid was the medium of vision and flowed from the eye to the brain via 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.

Pre-Hippocrates
Alexandrian studies extensively contributed to knowledge of the eye. Aëtius tells us that Herophilus dedicated an entire study to the eye which no longer exists. In fact, no manuscripts from the region and time are known to have survived, leading us to rely on Celsius' account—which is seen as a confused account written by a man who did not know the subject matter. From Celsius it is known that the lens had been recognised, and they no longer saw a fluid flowing to the brain through some hollow tube, but likely a continuation of layers of tissue into the brain. Celsius failed to recognise the retina's role, and did not think it was the tissue that continued into the brain.

Alexandrian studies
Rufus recognised a more modern 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 an egg-white-like substance). Galen remedied some mistakes including the curvature of the cornea and lens, the nature of the optic nerve, and the existence of a posterior chamber. Though this model was roughly a correct but simplistic modern model of the eye, it contained errors. Yet 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, though he dissected the optic nerve, and saw it was solid, He mistakenly counted seven optical muscles, one too many. He also knew of the tear ducts.

Rufus
After Galen a period of speculation is again noted by Arab scientists - the lens modified Galen's model to place the lens in the middle of the eye, a notion which lasted until Vesalius reversed the era of speculation. However, Vesalius was not an ophthalmologist and taught that the eye was a more primitive notion than the notion of both Galen and the Arabian scientists - the cornea was not seen as being of greater curvature and the posterior side of the lens wasn't seen to be larger.
Understanding of the eye had been so slow to develop because for a long time the lens was perceived to be the seat of vision, not as part of the pathway for vision. This mistake was corrected when Fabricius and his successors correctly placed the lens and developed the modern notion of the structure of the eye. They removed the idea of Galen's seventh muscle (the retractor bulbi) and reinstated the correct curvatures of the lens and cornea, as well as stating the ciliary body as a connective structure between the lens and the choroid.

After Galen

Main article: Ophthalmology in medieval Islam Muslim ophthalmology
The seventeenth and eighteenth century saw the use of hand-lenses (by Malpighi), microscopes (van Leeuwenhoek), preparations for fixing the eye for study (Ruysch) and later the freezing of the eye (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 of course the nature of the retina. In 1722 Leeuwenhoek noted the existence of rods and cones though they were not properly discovered until Gottfried Reinhold Treviranus in 1834 by use of a microscope.

Seventeenth and eighteenth century
The first ophthalmic surgeon was John Freke, appointed to the position by the Governors of St Bartholomew's Hospital in 1727, but the establishment of the first dedicated ophthalmic hospital in 1805 - now called Moorfields Eye Hospital in London, England was a transforming event in modern ophthalmology. Clinical developments at Moorfields and the founding of the Institute of Ophthalmology by Sir Stewart Duke-Elder established the site as the largest eye hospital in the world and a nexus for ophthalmic research.

First ophthalmic surgeon
Ophthalmologists are medical doctors (M.D.) or Doctors of Osteopathy (D.O.) who have completed medical school and completed a further four years post-graduate training in ophthalmology in many countries. Many ophthalmologists also undergo additional specialized training in one of the many subspecialities. Ophthalmology was the first branch of medicine to offer board certification, now a standard practice among all specialties.

Professional requirements
In the United States, four years of training after medical school are required, with the first year being an internship in surgery, internal medicine, pediatrics, or a general transition year. The scope of a physician's licensure is such that he or she need not be board certified in ophthalmology to practice as an ophthalmologist. The American Academy of Ophthalmology (AAO) promotes the use of the phrase "Eye MD" to distinguish ophthalmologists from optometrists who hold the degree OD (Doctorate in Optometry). (This, however, sometimes leads to confusion among patients, since a few ophthalmologists' primary medical degree is a D.O., or Doctor of Osteopathic Medicine, rather than an M.D. In both cases, the same residency and certification requirements must be fulfilled.) Completing the requirements of continuing medical education is mandatory for continuing licensure and re-certification. Professional bodies like AAO, ASCRS organise conferences and help members through CME programs to maintain certification, in addition to congress advocacy and peer support.

United States
In the United Kingdom, there are four colleges that grant postgraduate degrees in ophthalmology. The Royal College of Ophthalmologists grants MRCOphth and FRCOphth (postgraduate exams), the Royal College of Edinburgh grants MRCSEd, the Royal College of Glasgow grants FRCS and Royal College of Ireland grants FRCSI. Work experience as a specialist registrar and one of these degrees is required for specialisation in eye diseases.

United Kingdom
In Australia and New Zealand, the FRACO/FRANZCO is the equivalent postgraduate specialist qualification. They do not generally accept overseas-trained Ophthalmologists as having equivalent qualifications, except those who have completed their formal training in the UK.
On case by case basis, they will allow suitably-qualified Ophthalmologists to work in Area of Need positions, usually in regional areas. However, such appointments are generally only limited to South African/Canadian trained Ophthalmologists.

Australia and New Zealand
In India, after completing MBBS degree, post-graduation in Ophthalmology is required. The degrees are Doctor of Medicine (MD), Master of Surgery (MS), Diploma in Ophthalmic Medicine and Surgery (DOMS) or Diplomate of National Board (DNB). The concurrent training and work experience is in the form of a Junior Residency at a Medical College, Eye Hospital or Institution under the supervision of experienced faculty. Further work experience in form of fellowship, registrar or senior resident refines the skills of these eye surgeons. All India Ophthalmological Society (AIOS) and various state level Ophthalmological Societies (like DOS) hold regular conferences and actively promote continuing medical education.

India
In Pakistan, there is a residency program leading into FCPS which is composed of two parts.

Pakistan
In Canada, an Ophthalmology residency after medical school. A minimum of 5 years after the MD. degree although subspecialty training is undertaken by about 30% of fellows (FRCSC). There are about 30 vacancies per year for ophthalmology training in all of Canada.

Finland
Formal specialty training programs in veterinary ophthalmology now exist in some countries [4] [5] [6].

Veterinary
Ophthalmologists are trained and licensed to perform surgery and prescribe ocular, oral and systemic medications. They can manage diseases and conditions of the eye, the visual pathway, and structures surrounding the eye, with medical and/or surgical treatments. For example this may include:
Optometrists, or optometric physicians, are not medical doctors. Instead, optometrists usually receive 4-5 years training in vision science, eye health and optometry-related areas, sometimes following a bachelor's degree (usually in science) in some countries.
While both ophthalmologists and optometrists are trained in refraction, it is generally accepted that optometrists receive more thorough training in prescribing optical aids such as spectacles, contact lens and magnifiers.
The two fields often have a mutually beneficial relationship.

cataract extraction with intra-ocular lens replacement for cataracts,
laser refractive surgery on cornea for refractive error remediation
extra-ocular muscle surgery for strabismus,
prescribing topical medication, performing trabeculoplasty or iridotomy surgery for glaucoma
laser surgery for some retinal diseases
excision or biopsy of tumors on eyelid or in the eye
prescribing temporary topical medical treatment for amblyopia
Ophthalmologists may refer patients to optometrists for optical aids or low vision rehabilitation whilst continuing to treat the ocular disease/condition that may have reduced vision.
Both optometrists and ophthalmologists perform screening for common ocular problems affecting children (i.e., amblyopia and strabismus) and the adult population (cataract, glaucoma, and diabetic retinopathy). Optometrists may refer to ophthalmology for further assessment and medical treatment of ocular disease or condition.
Optometrists and ophthalmologists sometimes co-manage treatment of strabismus and amblyopia with a combination of vision therapy, medical or surgical treatment. Distinction from Optometry
Ophthalmology includes sub-specialities which deal either with certain diseases or diseases of certain parts of the eye. Some of them are:

Anterior segment surgery
Cataract - not considered a subspecialty per se, since most general ophthalmologists do surgery for this.
Cornea, ocular surface, and external disease
Glaucoma
Neuro-ophthalmology
Ocular oncology
Oculoplastics & Orbit surgery
Ophthalmic pathology
Pediatric ophthalmology/Strabismus (squint)
Refractive surgery
Retina and Vitreous (sometimes labelled as a posterior segment specialization)
Uveitis/Immunology Sub-specialities

Famous ophthalmologists

Eye examination
Eye care professional
History of eye colors
Ophthalmology in medieval Islam
Optometry
Optics
Orthoptics
Prentice position