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Onchocerciasis is one of four major causes of blindness in the world. The other three are trachoma, xerophthalmia, and cataracts. The disease occurs primarily in developing countries, mainly in West Equatorial Africa, Central America, and South America. According to Helen Keller International, onchocerciasis has affected over 30 million people, blinding over a million and a half. It is projected that twenty percent of those infected will become visually impaired. Onchocerciasis is also known as “river blindness” because of its association to vector breeding sites. The infection is a systemic disease caused by the filarial worm Onchocerca volvulus, a parasite transmitted by the blackfly. Humans become infected with the disease when the worm infiltrates the body through tainted water or direct contact. The worm may live up to fifteen years within the human skin, kidneys, blood, or cerebrospinal fluid. The disease causes corneal inflammation or keratitis, corneal scarring, and vision loss. It may be seen in conjunction with chronic iridocyclitis and glaucoma. Although there are antiparasitic medications to combat the disease, they are unaffordable to the ones who need them most. Other preventative measures include the use of insecticides to rid the community of the worms, avoidance of such breeding sites as rivers or open waterway, wearing protective clothing, and excising of skin nodules that contain the worms. However, none of these methods gets to the heart of the problem, which is access to clean water and food.

Opacification is a cloudiness or lack of transparency that blocks the transmission of light. This usually refers to a clouding of the eye lens, which leads to cataracts. Opacities in the lens are very common in ageing eyes and are not termed cataract until the opaque lens fibers significantly interfere with vision. Opacities often progress so gradually that the patient is unaware of the cataract until it becomes large or crosses the center of vision. Opacities that do develop into cataracts can be removed through surgery, where satisfactory results are achieved in ninety percent of the cases.

Opthalmia neonatorum is an inflammation of the eyes of newborns. The condition generally affects the cornea and conjunctiva. The inflammation is transferred from the mother to the infant’s eyes as the child passes through the birth canal. The condition is not hereditary but occurs during the birthing process. Once a common cause of blindness arising from unhygenic conditions at birth, the infection is now successfully treated with antibiotics immediately after birth. Such bacteria as gonococcus, staphylococcus, streptococcus, or pneumococcus, as well as such viral infections as chlamydia, are present within the maternal birth canal. A herpes infection is the most common infection transmitted at birth, followed closely by other microbial infections. Symptoms of an infection are apparent shortly after birth when the cornea, conjunctiva, and eyelids of the infant begin to inflame. The eyes may be treated with local antibiotics. The standard postbirth treatment is the administration of silver nitrate to all newborns whether there is a possibility of an infection or not. Systemic antibiotics will be used if the cornea is involved. If not treated, the condition can cause blindness and spread to other parts of the body.

Ophthalmic technician (certified) assists ophthalmologists by taking patient histories and performing a number of tests. They may also be qualified to do some contact lens fittings. Many such technicians are ophthalmic nurses who received additional training to earn certification.

Ophthalmodynamometer is an instrument specifically designed to measure the systolic and diastolic blood pressure of arterioretinal vessels. It will often detect increasing intracranial pressure before other symptoms appear. However, this instrument is giving way to more sophisticated methods.

Opthalmologist is a medical doctor, a graduate of an accredited medical school with an MD degree but one who specializes in the eyes. This means that the person will have a good understanding of illnesses the happen to the rest of the body that, in turn, affect eyesight. An ophthalmologist has been through college, four years of medical school, one year of internship, and at least three years of specialized residency training in diseases and surgery of the eye, which includes extensive written and oral examinations. Some go on to subspecialize, meaning one or two more years of training in just one type of eye disease. A corneal surgeon who performs corneal transplants or a retinal surgeon who only does surgery for detached retinas are two examples of subspecialization. Cataract surgeons are generally ophthalmologists who develop their skills during three or more years of residency training and enter private practice or hospital practice after their training is completed. They learn new techniques in courses given throughout the country or by visiting and operating with experts in the field. Some ophthalmologists provide total eye care, beginning with the comprehensive medical eye exam, prescribing corrective eyewear, diagnosing eye diseases and treatments, and performing the appropriate medical, surgical, and laser procedures. However, most specialize rather than offer total eye care.

Ophthalmoscope is a hand-held instrument through which the ophthalmologist focuses on the back of the eye. A medical doctor will also use one to uncover any effects of high blood pressure and diabetes in the eyes. The problem with the instrument is that it does not emit a strong enough light to see through a cataract. Another type of ophthalmoscope is the binocular indirect ophthalmoscope which emits an extremely strong light that, except for very dense cataracts, will allow an eye doctor a sufficiently clear view of the retina to predict whether it is normal. If the retina is not normal, removing the cataract will not improve vision enough to warrant an operation.

Optician is an eye care professional trained and licensed to take a prescription from an eye doctor and then grind and formulate the lenses to make the specific eyeglasses needed by the individual. They will fit, adjust, and dispense eyeglasses and other optical devices following the written prescription of an ophthalmologist or optometrist. In some cases, opticians are licenced to fit and dispense contact lenses, but are not trained or licenced to examine the eye.

Optic atrophy is a loss of nerve tissue on the optic disc, the area where the optic nerve joins the eye. The optic disc is nonseeing and corresponds to the blind spot in vision. Optic atrophy may cause a loss of visual field. Both the central and side (peripheral) vision may be lost, although visual acuity may remain unaffected. It can also cause abnormal color vision or blurred vision. Often called “pale disc”, optic atrophy is characterized by pallor (whiteness) of the disc. Because nearsighted eyes and those of children also have disc pallor, the condition may be misdiagnosed or confused with other conditions. Optic atrophy may be caused by glaucoma, an obstruction of a retinal vein or artery, a disorder of the optic nerve as optic neuritis, a tumor, papilledema (swelling of the disc due to intracranial pressure), retinitis pigmentosa, toxic-related causes (as tobacco amblyopia), or injury. Treatment consists of therapy for the underlying causes.

Optic disc(k) is part of the retina where the optic nerve meets the eye and the blood supply enters the eye. The optic disc contains no light-sensitive rods or cones, so it is not able to “see.” It is responsible for the blind spot in normal vision and is subject to swelling. Papilledema is a condition that occurs when the optic disc becomes swollen because of an obstruction to the circulation of blood within the eye or by increased pressure within the cranium. Swelling may also be caused by optic neuritis (swelling of the optic nerve), blockage of a central retinal vein resulting from arterial disease, multiple sclerosis, diabetic retinopathy, and postoperative conditions following intraocular surgery.

Optic nerve is the communication “cable” between the eyes and the brain. Visual information is gathered by the retina and carried to the visual cortex of the brain by a bundle of over one million nerve fibers, called the optic nerve. The yellowish-circle visible on the retina is where the optic nerve forms at the back of the eye. This location is called the optic disk. The optic nerve is the second cranial nerve. It is purely sensory and is concerned only with carrying impulses for the sense of sight. The rods and cones of the retina are connected with the optic nerve which leaves the eye slightly to the nasal side of the center of the retina. The point at which the optic nerve leaves the eye is called the “blind spot” because there are no rods and cones in this area. The optic nerve passes through the optic foramen of the skull and into the cranial cavity. It then passes backward and undergoes a division. Those nerve fibers leading from the nasal side of the retina cross to the opposite side. Those from the temporal side continue to the thalamus uncrossed. After synapsing in the thalamus, the neurons convey visual impulses to the occipital lobe of the brain. Degenerative and inflammatory lesions of the optic nerve can occur as a result of infections, toxic damage to the nerve, metabolic or nutritional disorders, or trauma. Syphilis is the most frequent cause of infectious disorders of the optic nerve. Methanol (methyl alcohol) is highly toxic to the optic nerve and can cause total blindness. Diabetes and anemia are examples of metabolic and nutritional disorders that can lead to damage of the optic nerve and produce serious loss of vision. Treatment of optic neuritis is aimed at control of the primary cause. However, despite treatment nothing can be done to regain lost sight through damage to the nerve.

Optic neuropathy, or neuritis is a swelling of the optic nerve. The condition is serious and may result in permanent vision loss. Optic neuropathy is often associated with multiple sclerosis. This form of neuritis, called retrobulbar neuritis, involves sudden loss of vision in one eye accompanied by pain associated with eye movement. Blind spots (scotomas) may appear within the field of vision, as well as color blindness and difficulty seeing in bright light. Vision may be affected in the entire field or may begin in the center of the field and progress to peripheral areas. It is usually treated with steroids, and vision may be partially or completely restored after three months. Optic neuropathy unrelated to multiple sclerosis may be caused by such collagen disease as lupus; vascular disease as arteriosclerosis, arteritis, or arterial hypertension; a viral, fungal, or bacterial infection; tumors or cysts; or overuse of alcohol and tobacco and other toxic substances. There is also a hereditary form that affects more males than females and usually surfaces in the mid-twenties. This type of optic neuropathy is called leberis hereditary optic neuropathy. Symptoms may include loss of vision in one or both eyes.

Optometric technician assists optometrists by taking patient histories and performing some routine tests.

Optometrist is someone who has earned a doctor of optometry (OD) degree after completing four years of post-graduate-level optometry school, following a four-year undergraduate college degree. He is not a medical physician. Optometry school covers the structure and function of the eye, mechanisms of vision and optics, and the diagnosis and treatment of eye diseases and disorders. Some optometry schools have developed collaborative arrangements with medical schools to give optometry students the opportunity to develop a better understanding of how the eye relates to the human body and its overall condition. Optometrists traditionally limit their scope of practice to nonmedical treatment of eye problems. This includes prescribing corrective lenses and the use of vision therapy to improve overall functioning of the visual system.

Orbital cellulitis is an inflammation of the orbit. The infection is considered an emergency and must be treated promptly. If untreated, the optic nerve may become damaged and vision permanently lost. If allowed to spread to the brain, the infection could cause meningitis. Orbital cellulitis may be the result of a sinus infection that spreads to the bony orbit socket. Symptoms include forward displacement of the eye, restricted ocular motility, fever, and red, swollen eyelids. Movement of the eye also may be limited. Treatment involves admission to the hospital where antibiotics are administered in intensive therapy. Surgery may be performed to drain an abscess. If treatment is timely, prognosis is excellent for the eye and vision.

Orthokeratology is a procedure that uses contact lenses to reshape the cornea to reduce myopia. The curvature of the cornea is measured and hard contact lenses are prescribed at a slightly flatter degree. As the cornea is flattened, new lenses are prescribed at increasingly flatter degrees. The process may take up to three years to complete after which, the cornea may maintain its new shape for a period of time but, eventually, reverts to its original shape. Retainer lenses may be prescribed to discourage regression and may be worn for as little as once a month or as much as eight hours a day. Objective analysis of the procedure has revealed dangers of permanent damage to the cornea, unimpressive and transient success rates, discomfort during the process, and the expense. Those with mild myopia stand the best chance of success, but those with severe myopia may benefit only in a reduction of strength needed in the lens prescription. The procedure, although acclaimed by some doctors, is not widely practiced.

Orthoptist is a skilled health-care worker who diagnoses and treats people who have fused-vision, eye-muscle, and crossed-eye disorders. Orthoptists may also specialize in eye exercises, primarily for children with strabismus. They work under supervision of an ophthalmologist to teach patients vision exercises that enable the patient to accurately focus and coordinate the movement of both eyes. They may also be trained in glaucoma and vision-field testing. Orthoptists must complete a minimum of two years of college or registered nurse’s training in addition to the two years orthoptist academic program offerred by hospitals, medical schools, or eye clinics. They may be certified by the American Orthoptic Council, although this is not a requirement for employment. Orthoptists were more common in the 1940s and 1950s than they are today. Most of the ones who started out as orthoptists became certified ophthalmic technicians.