OCANZ COE cheat sheet
OCANZ COE · Keep the key ideas within reach.
Written Examination: Optometry Knowledge and Clinical Reasoning
Spherical equivalent = sphere + (cylinder/2); used to compare refractive error magnitude and to estimate retinal image blur when astigmatism is present.
Snellen fraction converts to logMAR: logMAR = log10(denominator/numerator); 6/6 = 0.00, 6/12 = 0.30, 6/60 = 1.00.
Age-related expected amplitude of accommodation (D) approximates 18.5 − 0.30 × age (Hofstetter minimum formula uses 15 − 0.25 × age).
Intraocular pressure measured by Goldmann applanation tonometry is affected by central corneal thickness: thicker corneas read falsely high, thinner read falsely low.
Cup-to-disc ratio progression, disc haemorrhage, and neuroretinal rim thinning (especially inferior and temporal) are structural glaucoma indicators independent of visual field loss.
Amsler grid testing screens for macular disease; metamorphopsia indicates distortion of the central 10 degrees and warrants fundus examination.
Normal tear break-up time is generally 10 seconds or more; shorter values suggest evaporative dry eye or meibomian gland dysfunction.
Prism dioptre relates to deviation angle by Prentice's rule: prism (Δ) = decentration in cm × lens power in dioptres.
Colour vision testing with Ishihara plates detects red-green defects; acquired blue-yellow loss is more typical of optic nerve or retinal disease.
Clinical Examination: Optometric Clinical Competence
Cover test: alternate occlusion to reveal total deviation (tropia); uncover test to detect recovery movement and differentiate phoria from tropia.
Hirschberg test estimates angle by corneal light reflex position: roughly 15° per 1 mm of reflex displacement from pupil centre.
Retinoscopy working distance lens equals the inverse of the working distance in metres (e.g., 0.67 m requires +1.50 D subtraction).
Monocular estimation method (MEM) retinoscopy uses lenses over the distance correction while the patient reads near targets to estimate accommodative lag.
Direct ophthalmoscopy gives approximately 15× magnification and an upright, non-reversed view; indirect gives an inverted, reversed view.
Gonioscopy with a mirrored lens allows angle assessment; Shaffer grading 0-4 describes angle openness, with grade 0-1 indicating closure risk.
Worth 4-dot test distinguishes suppression (missing dots) from diplopia (five dots) and confirms binocular single vision (four dots).
Stereopsis thresholds of 40-60 seconds of arc on random-dot tests indicate normal fine binocular depth perception.