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Eye Health Glossary

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ocular hypertension

Elevated pressure within the eye (IOP). High IOP is an important risk factor for glaucoma.

ocular migraine

Type of migraine in which visual symptoms are prominent, with or without headache.

OD

1. Oculus dexter; right eye, 2. Doctor of Optometry.

onchocerciasis

River blindness; infestation with Onchocerca volvulus roundworms (filaria) that are transferred to humans with the bite of a black fly. Onchocerciasis is the second-leading cause of blindness in the world.

ophthalmologist

Medical doctor who specializes in care and treatment of eyes. While it varies from state to state with limitations on optometrists, most therapeutic and refractive eye surgeries are performed by ophthalmologists.

ophthalmoplegia

Paralysis of one or more of the eye muscles.

ophthalmoscope

Figure: Binocular Indirect Ophthalmoscope. Courtesy of National Eye Institute.

Ophthalmic instrument that is used to view the inside of the eye through the pupil. The direct ophthalmoscope is a handheld instrument with very high magnification but low field of view while the binocular indirect ophthalmoscope (See Figure) enables viewing of the entire inside of the eye (fundus) with the unfortunate consequence of much having reduced magnification.

opsoclonus

Rapid, erratic, uncontrollable oscillations and jerky movements of the eyes; sometimes observed in various brain stem and cerebellum disorders.

optic cup

White cup-like area that forms the center of the optic disc.

optic disc

Area of the eye where the retina connects to the optic nerve. There are no photoreceptors in this region and as a result, the area in visual space that corresponds to the optic disc is known as a blind spot because there is no vision in this area.

optic fissure

A gap the opens during development of the eyes. Nourishment is provided to the developing eye via the optic fissure. The optic fissure must close before birth, or a coloboma may result.

optic nerve

The cranial nerve that connects the eye to the brain, carrying all visual information necessary for vision to occur. There are more than a million fibres contained within the optic nerve. Learn more about how vision works.

optic nerve head

The area at the back of the eye where the optic nerve attaches to the retina.

optician

A technician who is specially trained in the manufacturing, dispensing, and adjustment of eyeglasses and spectacles as well as contact lenses.

optometrist

An eyecare professional who is specially trained in assessment, diagnosis and (in some states) management of eye diseases, as well as in fitting contact lenses and prescribing lenses.

orbicularis oculi

Muscle that is responsible for closing the eyelids. The muscle fibers of the orbicularis oculi form a circle around the eyeball.

orbit

The cavity within which the eye, extraocular muscles, and supporting tissues reside. The orbit is formed from the shape of bones in the area and is quite apparent upon viewing a skeleton.

orthokeratology (ortho-k)

Use of hard contact lenses worn overnight to change the shape of the cornea such that during the day, no contact lenses or glasses are needed. Learn more about Ortho-K lenses and Corneal Refractive Therapy (CRT).

orthoptics

Visual training used as a non-surgical treatment option for binocular vision problems such as strabismus and amblyopia.

OS

Oculus sinister; left eye.

osteopetrosis

Aka. Albers-Schonberg Disease; extremely rare hereditary condition in which bone density is much higher than normal, making bones much more susceptible to being broken. Osteopetrosis can lead to blindness.

OU

Oculus uterque; both eyes.

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