COMT key terms

The clear, dome-shaped front window of the eye that bends (refracts) incoming light and protects the structures behind it. It has no blood vessels and receives oxygen directly from the air and tears.

Clear fluid produced by the ciliary body that fills the anterior chamber and nourishes the cornea and lens. It drains through the trabecular meshwork into Schlemm's canal, and the balance of production and outflow sets intraocular pressure.

Spongy drainage tissue located in the angle where the iris meets the cornea. Aqueous humor filters through it into Schlemm's canal before entering the bloodstream; blockage raises intraocular pressure.

Small central area of the retina packed with cone photoreceptors that provides sharp, detailed central vision and color perception. Its center, the fovea, is the point of highest visual acuity.

The round area at the back of the eye where retinal nerve fibers bundle together and exit as the optic nerve. It has no photoreceptors, creating the natural blind spot; the cup-to-disc ratio is assessed here.

Clouding of the eye's natural crystalline lens that scatters light and reduces vision, often causing glare and faded colors. It is most commonly age-related and is treated by surgical lens removal and replacement.

A progressive optic nerve disease in which retinal ganglion cells are lost, producing characteristic visual field defects. The drainage angle appears open but aqueous outflow is impaired, and pressure is often elevated.

A corneal disorder in which the cornea progressively thins and bulges into a cone shape, creating irregular astigmatism and blurred vision. It often begins in adolescence and may be managed with rigid contact lenses or collagen cross-linking.

Reduced best-corrected vision in one or both eyes caused by abnormal visual development during childhood, without visible structural damage. Treatment aims to force use of the weaker eye, often by patching.

Separation of the light-sensitive retina from the underlying retinal pigment epithelium, which cuts off its blood supply. Symptoms include flashes, floaters, and a curtain-like shadow; it is a sight-threatening emergency.

Inflammation of the uvea - the iris, ciliary body, and choroid - that can cause pain, redness, light sensitivity, and floaters. It may be infectious or autoimmune and can lead to serious complications if untreated.

A mismatch between the eye's focusing power and its length, so light does not focus sharply on the retina. Myopia, hyperopia, and astigmatism are the main types, corrected with glasses, contact lenses, or surgery.

A refractive condition in which light from distant objects focuses in front of the retina, making far vision blurry while near vision stays clear. It is corrected with minus (concave) lenses.

A refractive condition in which light focuses behind the retina when the eye is relaxed, so near objects are blurred. Young patients may compensate by accommodating; plus (convex) lenses correct it.

A refractive error in which the cornea or lens has unequal curvature in different meridians, so light forms two focal lines instead of one point. Vision is blurred and distorted at all distances.

Age-related loss of the eye's ability to focus on near objects, caused by stiffening of the crystalline lens and weakening of the ciliary muscle. It typically becomes noticeable in the 40s.

The distance between the back surface of a spectacle lens and the front of the cornea. It matters most for higher-powered lenses, because changing it alters the effective power at the eye.

Measurement of the curvature of the central cornea, reported as radius of curvature and dioptric power in two meridians. It is used for contact lens fitting, astigmatism assessment, and intraocular lens calculations.

The curvature of a contact lens's back surface, chosen to fit the shape of the cornea. A well-matched base curve allows the lens to center, move properly, and avoid binding or excessive rocking.

A unit describing prism power, defined as a displacement of one centimeter at a distance of one meter. It is used to measure and correct strabismus and to prescribe prism in glasses.

A single number summarizing a spherocylindrical prescription, calculated by adding half the cylinder power to the sphere. It is commonly used for contact lens ordering and refractive surgery planning.

A method of estimating intraocular pressure by measuring the force needed to flatten a fixed area of the cornea. Corneal thickness and rigidity can affect the reading.

A slit-lamp-mounted device that flattens a 3.06 mm area of the anesthetized, fluorescein-stained cornea. It is considered a reference standard for intraocular pressure measurement.

Testing that maps the visual field by presenting lights at various locations and recording which ones the patient sees. It detects and monitors field loss from glaucoma and neurological disease.

A non-contact imaging test using low-coherence light to create cross-sectional pictures of the retina and optic nerve. It measures layer thickness and helps diagnose macular and glaucomatous disease.

A two-dimensional ultrasound scan of the eye that shows cross-sectional anatomy. It is useful when the view into the eye is blocked by cataract, hemorrhage, or a dense lens.

An ultrasound measurement of the eye's axial length, used with corneal power to calculate the power of an intraocular lens before cataract surgery. The probe is aligned along the visual axis.

Measurement of corneal thickness, usually by ultrasound or optical methods. Thickness influences the accuracy of tonometry, and thin corneas are associated with glaucoma risk.

A test in which fluorescein dye is injected into a vein and rapid photographs record its passage through the retinal vessels. It reveals leakage, blockage, and abnormal new vessel growth.

A drug that enlarges the pupil by relaxing the iris sphincter or stimulating the dilator muscle. Mydriatics such as phenylephrine and tropicamide allow examination of the retina and lens.

A drug that temporarily paralyzes the ciliary muscle and dilates the pupil, preventing accommodation. Cyclopentolate and atropine are used for cycloplegic refraction, especially in children.

Anesthetic eye drop, such as proparacaine or benoxinate, that numbs the surface of the eye within seconds. It is used for tonometry, foreign body removal, and minor procedures, but not for long-term pain relief.

A device that sterilizes instruments using pressurized steam at high temperature. Proper loading, monitoring, and packaging are needed to kill all microorganisms, including bacterial spores.

Delivery of medication, such as an anti-VEGF drug or steroid, directly into the vitreous cavity through the pars plana. It is used for macular degeneration, diabetic eye disease, and retinal vein occlusion.

Cataract surgery technique in which an ultrasonic handpiece breaks up and aspirates the clouded lens through a small incision. The remaining capsule holds a folded intraocular lens implant.

A defined work area in which all instruments and supplies are free of microorganisms. Staff maintain it by wearing gloves, avoiding contact with non-sterile surfaces, and keeping the field in view.

A measure of central vision using rows of letters of decreasing size viewed at a set distance. Results are recorded as a fraction, such as 20/20, comparing the patient to a standard observer.

The process of explaining a procedure's purpose, risks, benefits, and alternatives so the patient can voluntarily agree or decline. It should be documented and obtained before treatment or surgery.

A U.S. federal law that protects the privacy and security of individually identifiable health information. It governs how eye care practices use, disclose, and safeguard patient records and communications.

A system of numeric codes describing medical procedures and services for billing and claims. Correct codes are chosen from documentation of the examination, tests, and treatments performed.