NBEO Part III flashcards

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

Pinhole test purpose

Determines whether reduced visual acuity is due to refractive error; improvement suggests refractive cause, no improvement suggests ocular media or retinal/neural cause.

Snellen 20/20 definition

A letter subtending 5 arc minutes at 6 meters (20 feet); each detail subtends 1 arc minute; represents normal central visual acuity.

Jackson cross-cylinder technique

Uses a ±0.25 D cross-cylinder to refine astigmatism; axis checked with JCC at 45° to correcting axis; power checked with JCC aligned to axis.

Duochrome test principle

Red and green targets compared; in emmetropia they appear equally clear; red clearer indicates myopia (add minus); green clearer indicates hyperopia (add plus).

Cycloplegic refraction indication

Used in children, accommodative esotropia, and patients with unreliable manifest refraction; cyclopentolate 1% or atropine 1% paralyzes accommodation.

Keratometry measurement

Measures anterior corneal curvature over central 3 mm; average K ~43.00 D; astigmatism calculated as difference between steep and flat meridians.

Cover test interpretation

Cover one eye and observe uncovered eye; movement indicates deviation; recovery movement after uncover distinguishes phoria from tropia.

Near point of convergence

Target moved toward nose until patient reports diplopia or one eye deviates; normal break <5 cm and recovery <7 cm; receded NPC suggests convergence insufficiency.

Worth 4-dot test

Red-green glasses with 4 dots; 4 dots indicates fusion; 2 red indicates left suppression; 3 green indicates right suppression; 5 dots indicates diplopia.

Hirschberg test

Corneal light reflex displacement from pupil center estimates strabismus; 1 mm displacement ≈ 7° or ~15 prism diopters deviation.

Stereopsis normal value

Randot or Titmus test; normal stereoacuity is 40-60 seconds of arc; absence suggests monocular vision, suppression, or strabismus.

Van Herick technique

Slit lamp grading of peripheral anterior chamber depth; grade 0-4; grade ≤2 indicates shallow AC and risk of angle closure glaucoma.

Seidel test

Fluorescein applied to suspected corneal wound; streaming aqueous humor indicates full-thickness laceration; positive test requires urgent referral.

Sclerotic scatter illumination

Broad beam at limbus; light scattered through cornea reveals subtle opacities, edema, and epithelial defects.

Retroillumination technique

Light reflected from iris or fundus; highlights corneal endothelial guttata, pigment deposits, and lens opacities.

Indirect ophthalmoscopy image

Condensing lens (20 D or 28 D) with headset; produces inverted, reversed, real image; wide field for peripheral retina evaluation.

Cup-to-disc ratio

Ratio of optic cup diameter to disc diameter; normal ≤0.5; asymmetry >0.2 between eyes or CDR ≥0.6 warrants glaucoma evaluation.

ISNT rule

Neuroretinal rim thickness order: Inferior > Superior > Nasal > Temporal; violation suggests glaucomatous damage.

Amsler grid purpose

10 cm grid at 33 cm; detects central 10° metamorphopsia and scotomas; used in macular degeneration monitoring.

Goldmann applanation tonometry

Measures IOP by flattening corneal area of 3.06 mm diameter; normal 10-21 mmHg; affected by central corneal thickness.

Central corneal thickness effect

Thin CCT (<500 µm) underestimates true IOP; thick CCT (>600 µm) overestimates; pachymetry needed for accurate interpretation.

Shaffer gonioscopy grading

Grades angle width from 0 (closed) to 4 (wide open); grade ≤2 indicates narrow angle and risk of closure.

Glaucomatous visual field defect

Nasal step, arcuate scotoma, paracentral scotoma, or altitudinal defect; respects horizontal midline; confirmed with repeat testing.

Humphrey reliability indices

Fixation losses, false positives, and false negatives should be <33%; higher values indicate unreliable field test requiring repeat.

Soft contact lens fit

Centration, full corneal coverage, 0.5-1.0 mm movement with blink, no limbal compression; push-up test assesses tightness.

RGP fluorescein pattern

Apical clearance or alignment, edge lift 0.1-0.2 mm, and centration; pattern guides base curve adjustment.

Tear film breakup time

Normal >10 seconds; <5 seconds indicates dry eye; may contraindicate contact lens wear and warrants tear supplementation.

Vertex distance formula

Effective power change = (F × d)/(1 - dF); compensate when refractive error exceeds ±4.00 D or when switching between spectacles and contact lenses.

Prentice rule

Prism diopters = decentration in cm × lens power in diopters; used to calculate induced prism from lens decentration.

Spherical equivalent

Sphere power + half cylinder power; used for rough estimation and contact lens conversion.

Cyclopentolate 1% properties

Anticholinergic cycloplegic; onset 30-60 minutes; duration 6-24 hours; used for cycloplegic refraction in children.

Punctal occlusion technique

After instilling drops, press on lacrimal sac for 1-2 minutes; increases ocular absorption and reduces systemic side effects.