COT flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Goldmann applanation normal range

Applanation tonometry measures IOP by flattening a fixed corneal area; normal intraocular pressure is generally 10 to 21 mmHg, and central corneal thickness alters the reading.

Punctal occlusion purpose

Applying pressure at the medial canthus for one to two minutes after drop instillation blocks nasolacrimal drainage, reducing systemic absorption and increasing corneal contact time.

Cyclopentolate duration

Cyclopentolate 1% is a cycloplegic that paralyzes the ciliary muscle and dilates the pupil; its effect typically lasts 24 to 72 hours, longer than tropicamide.

Amsler grid test distance

The Amsler grid is a 10 cm card covering about 20 degrees of central field, viewed at 33 cm with reading correction to detect metamorphopsia or central scotoma.

Chemical burn first action

For any ocular chemical exposure, immediate copious irrigation with saline or water precedes acuity testing and examination, because duration of contact drives tissue damage.

Tropicamide duration of action

Tropicamide 0.5% to 1% is a short-acting anticholinergic mydriatic with weak cycloplegia; dilation typically resolves within four to six hours.

Keratometry conversion formula

Keratometry converts anterior corneal radius of curvature in millimeters to dioptric power using K equals 337.5 divided by radius, assuming a standard refractive index.

Average axial length

A-scan ultrasonography measures eye length; the average adult phakic eye is about 23.5 to 24.0 mm, and greater length correlates with myopia.

Humphrey 24-2 spacing

The 24-2 visual field program tests 54 points spaced 6 degrees apart across the central 24 degrees, while the 10-2 program uses 2-degree spacing for macular defects.

Central corneal thickness average

Pachymetry measures corneal thickness; the average central value is roughly 540 to 550 microns, and thinner corneas can make applanation tonometry underestimate true pressure.

Sclerotic scatter technique

Sclerotic scatter directs a narrow slit beam at the limbus; light travels through the cornea by total internal reflection, making subtle opacities and edema visible.

Indirect ophthalmoscopy 20D lens

A 20-diopter condensing lens used with indirect ophthalmoscopy provides about 3x magnification and a 45-degree field, producing an inverted and reversed aerial image.

Tear breakup time normal

After fluorescein instillation, the interval until the first dry spot appears under cobalt blue illumination is normally greater than 10 seconds; shorter times suggest evaporative dry eye.

Keratoconus topography pattern

Corneal topography in keratoconus typically shows inferior steepening with an asymmetric bow-tie pattern, plus against-the-rule or oblique astigmatism and displaced apex.

OCT imaging principle

Optical coherence tomography uses low-coherence interferometry to produce cross-sectional retinal images; normal central macular thickness is roughly 250 to 270 microns.

Corneal endothelial function

The corneal endothelium is a nonregenerating monolayer that maintains corneal deturgescence through Na+/K+ ATPase pumps, keeping the stroma relatively dehydrated and clear.

Aqueous humor outflow pathway

Aqueous humor flows from the ciliary epithelium into the posterior chamber, through the pupil into the anterior chamber, then through the trabecular meshwork and Schlemm canal.

Foveal anatomy features

The fovea contains only cones, lacks retinal blood vessels, and shows near one-to-one cone-to-ganglion cell convergence, giving the highest visual acuity.

Nuclear sclerotic cataract effect

Nuclear sclerosis yellows and hardens the lens nucleus, increasing refractive index and producing a myopic shift, sometimes called second sight in early stages.

Proliferative diabetic retinopathy

Proliferative diabetic retinopathy is characterized by retinal neovascularization driven by vascular endothelial growth factor, often treated with panretinal photocoagulation or anti-VEGF injections.

Glaucomatous disc cupping

Glaucoma produces optic disc cupping with cup-to-disc ratio above about 0.6, neuroretinal rim thinning, and retinal nerve fiber layer loss, reflecting ganglion cell death.

Presbyopia onset age

Presbyopia results from loss of crystalline lens elasticity, reducing accommodative amplitude; it becomes symptomatic near age 40 to 45 and is corrected with near addition.

Cherry-red spot mechanism

In central retinal artery occlusion the inner retina whitens from ischemia, but the fovea stays red because it is supplied by the choroidal circulation, creating a cherry-red spot.

Spherical equivalent formula

Spherical equivalent equals the sphere power plus half the cylinder power; for example, minus 2.00 with minus 1.00 cylinder gives minus 2.50 diopters.

Vertex distance conversion

Compensated power equals original power divided by one minus vertex distance in meters times power; the correction matters clinically above about four diopters.

Prism diopter definition

One prism diopter deviates a light ray by 1 cm at a distance of 1 m; the Prentice rule states prism equals decentration in centimeters times lens power.

Simple magnifier magnification

For a simple magnifier with the eye relaxed at infinity, magnification equals 25 cm divided by the lens focal length in centimeters.

With-the-rule astigmatism axis

With-the-rule astigmatism has the steeper meridian near 180 degrees, corrected with a plus cylinder axis near 90 or minus cylinder axis near 180.

Silicone hydrogel advantage

Silicone hydrogel contact lenses have high oxygen transmissibility, often Dk/t above 100, reducing hypoxic complications and permitting extended wear schedules.

Rigid lens tear lens effect

A rigid gas permeable lens creates a tear layer between lens and cornea that neutralizes irregular corneal astigmatism, improving acuity compared with soft lenses.

Hydrogen peroxide lens care

Hydrogen peroxide contact lens systems require full neutralization, typically about six hours, before lens insertion; inserting early causes severe stinging and corneal irritation.