COA flashcards
COA · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Snellen 20/40 meaning
- The patient reads at 20 feet a line a standard eye reads at 40 feet, so the letter must be twice normal size; the larger denominator indicates poorer acuity.
- Spherical equivalent formula
- Add half the cylinder power to the sphere. A refraction of +1.00 -2.00 x 090 equals plano (0.00) spherical equivalent.
- Prism diopter definition
- One prism diopter displaces an image 1 cm at a distance of 1 meter, equivalent to 100 times the tangent of the deviation angle.
- Vertex distance effect
- Effective power changes when a lens moves from the spectacle plane to the cornea; the effect is clinically significant above roughly 4 diopters.
- With-the-rule astigmatism
- The steepest corneal meridian is vertical, near 90 degrees, so a minus cylinder axis is placed near 180 degrees to correct it.
- Aqueous humor outflow pathway
- Aqueous is made by ciliary epithelium, passes through the pupil, and drains mainly through trabecular meshwork into Schlemm canal and episcleral veins.
- Corneal endothelial function
- The endothelium does not regenerate and pumps fluid out of the stroma, keeping the cornea clear; failure causes stromal edema and haze.
- Rods versus cones
- Rods support dim-light and peripheral vision and lack color; cones concentrate in the fovea and mediate acuity and color vision.
- Physiologic blind spot
- The optic nerve head lacks photoreceptors, creating a scotoma about 15 degrees temporal to fixation in each eye.
- Accommodation mechanism
- Ciliary muscle contraction slackens the zonules, letting the lens round up and increase power for near focus; lens stiffening causes presbyopia.
- Normal intraocular pressure range
- Adult IOP typically falls between 10 and 21 mmHg; values outside this range warrant evaluation but do not alone diagnose glaucoma.
- Atropine cycloplegic duration
- Atropine is the longest-acting cycloplegic, with effects lasting up to 1 to 2 weeks, unlike short-acting tropicamide which lasts hours.
- Phenylephrine action
- A direct alpha-1 agonist that dilates the pupil without cycloplegia; it can elevate blood pressure in susceptible patients.
- Timolol contraindications
- This topical beta-blocker lowers IOP by reducing aqueous production and should be avoided in asthma and heart block.
- Latanoprost mechanism
- A prostaglandin analog that increases uveoscleral outflow; common effects include iris darkening and eyelash lengthening.
- Punctal occlusion purpose
- Applying pressure to the inner canthus for 1 to 2 minutes after a drop reduces drainage into the nose and systemic absorption.
- Spacing between eye drops
- Waiting about 5 minutes between different drops prevents the second drop from washing out the first and preserves each drug's effect.
- Topical anesthetic limits
- Agents such as proparacaine act within seconds but only for minutes; chronic use is avoided because they mask injury and impair healing.
- Pinhole test interpretation
- Acuity improvement through a pinhole indicates refractive blur; no improvement suggests media opacity or retinal or neural disease.
- Cover test purpose
- It distinguishes a manifest deviation (tropia) from a latent one (phoria); alternate cover breaks fusion to reveal the total deviation.
- Amsler grid use
- The patient views a grid to detect central distortion or scotoma, screening for macular disease such as degeneration or edema.
- Ishihara plate purpose
- These plates screen for red-green color deficiency; a normal result does not rule out acquired blue-yellow defects.
- Near acuity testing distance
- Near acuity is checked at about 40 cm (16 inches) with a near card, recording the smallest line read and any add power used.
- Confrontation visual field
- A screening test comparing the patient's peripheral field with the examiner's at about 1 meter, useful for detecting gross field loss.
- Goldmann tonometry requirements
- Applanation tonometry uses fluorescein and a topical anesthetic; the prism tip is cleaned and dried between patients.
- Keratometry measurement
- It measures corneal curvature in diopters or millimeters, informing contact lens fitting and intraocular lens power estimation.
- Autorefraction role
- An objective estimate of refractive error that serves as a starting point; subjective refinement yields the final prescription.
- A-scan versus B-scan
- A-scan biometry measures axial length for IOL calculation; B-scan provides a two-dimensional view when media are opaque.
- Slit-lamp patient positioning
- Chin on the chin rest, forehead against the strap, and the canthus aligned with the marker on the support for stable viewing.
- Standard precautions principle
- All blood and body fluids are treated as potentially infectious; gloves are worn for contact with tears, blood, or mucous membranes.
- Sharps handling rule
- Used needles go directly into puncture-resistant containers; recapping by hand is avoided to prevent needlestick injury.
- HIPAA disclosure standard
- Protected health information may be shared for treatment, payment, or operations, or with patient authorization; otherwise it stays confidential.