OCANZ COE flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Spherical equivalent formula
- Sphere plus half the cylinder power. Used to summarise refractive error as a single value and estimate blur in astigmatic eyes.
- LogMAR conversion
- LogMAR equals the base-10 logarithm of the Snellen denominator divided by the numerator. 6/6 is 0.00 and 6/60 is 1.00.
- Hofstetter minimum amplitude formula
- Expected minimum amplitude of accommodation in dioptres approximates 15 minus 0.25 times age. Useful for judging whether accommodative amplitude is reduced.
- Corneal thickness and tonometry
- Goldmann applanation readings are influenced by central corneal thickness: thick corneas overestimate pressure and thin corneas underestimate it, requiring clinical interpretation.
- Glaucomatous disc signs
- Progressive cup enlargement, disc haemorrhage, and rim thinning, particularly inferiorly and temporally, indicate glaucomatous damage independent of field loss.
- Amsler grid purpose
- A screening test for macular disease. Metamorphopsia or scotoma within the central grid suggests macular pathology warranting fundus examination.
- Normal tear break-up time
- A tear break-up time of 10 seconds or more is generally normal. Shorter times suggest evaporative dry eye or meibomian gland dysfunction.
- Prentice's rule
- Prism dioptres induced equal decentration in centimetres multiplied by lens power in dioptres. Used to calculate prismatic effect of decentred lenses.
- Ishihara plate interpretation
- Ishihara plates detect congenital red-green colour deficiency. Acquired blue-yellow loss more often reflects optic nerve or retinal disease.
- Alternate cover test
- Alternating occlusion breaks fusion and reveals the total deviation. A tropia shows a refixation movement when the cover is removed.
- Uncover test purpose
- Removing a cover from one eye reveals a refixation movement if a manifest deviation exists, distinguishing tropia from phoria.
- Hirschberg test estimate
- Corneal light reflex displacement of about 1 mm from the pupil centre corresponds to roughly 15 degrees of ocular deviation.
- Retinoscopy working distance
- The working lens equals the inverse of the working distance in metres. At 0.67 m, subtract +1.50 D from the neutralising lens power.
- MEM retinoscopy
- Monocular estimation method places lenses over the distance correction while the patient reads a near target, estimating accommodative lag.
- Direct ophthalmoscopy view
- Direct ophthalmoscopy provides about 15 times magnification with an upright, non-reversed image, useful for optic disc and macular assessment.
- Indirect ophthalmoscopy view
- Indirect ophthalmoscopy produces an inverted and reversed image with a wider field, useful for peripheral retinal examination.
- Shaffer angle grading
- Shaffer grades 0 to 4 describe gonioscopic angle openness. Grades 0 and 1 indicate narrow or closed angles with elevated closure risk.
- Worth 4-dot interpretation
- Four dots indicate binocular single vision. Missing dots suggest suppression, while five dots indicate diplopia from failure of fusion.
- Normal stereopsis threshold
- Random-dot stereotests showing thresholds of 40 to 60 seconds of arc indicate normal fine binocular depth perception.
- Cover-uncover test sequence
- Cover one eye, observe the uncovered eye for movement, then uncover and observe recovery. Movement indicates manifest or latent deviation.
- Pupillary light reflex pathway
- Afferent limb travels via the optic nerve and pretectal area; efferent limb via the Edinger-Westphal nucleus and oculomotor nerve to both pupils.
- Relative afferent pupillary defect
- A reduced direct response in one eye with a stronger consensual response when light swings to it suggests optic nerve or extensive retinal disease.
- Confrontation visual field
- A quick bedside screening comparing the patient's field with the examiner's. Detects gross defects but lacks sensitivity for subtle loss.
- Duochrome test principle
- Red and green targets exploit chromatic aberration: clarity on red suggests over-minus, clarity on green suggests under-minus, guiding spherical refinement.
- Jackson cross-cylinder use
- A cross-cylinder flips between two meridians to refine astigmatic axis and power, presenting choices of equal blur to the patient.
- Near point of convergence
- The closest point at which the eyes maintain single binocular vision. Normal values are typically within 5 to 10 cm.
- Accommodative convergence ratio
- AC/A ratio describes convergence change per dioptre of accommodation. High values suggest convergence excess; low values suggest convergence insufficiency.
- Slit lamp biomicroscopy use
- Provides magnified illuminated views of anterior segment structures, allowing assessment of cornea, anterior chamber, iris, and lens.
- Van Herick technique
- Compares peripheral anterior chamber depth with corneal thickness at the slit beam. A ratio of one-quarter or less suggests angle closure risk.
- Optic nerve head assessment
- Evaluate disc size, cup-to-disc ratio, rim integrity, and peripapillary changes. Asymmetry and progressive cupping warrant glaucoma investigation.
- Ocular motility grading
- Extraocular muscle function is graded from 0 (full movement) to minus 4 (no movement) in each direction of gaze.
- Patient history structure
- A systematic history includes presenting complaint, ocular and medical history, medications, family history, and occupational visual demands.