Optometry Flashcards

A patient presents with a manifest refraction of -3.50 -1.25 × 045. When performing keratometry, you note readings of 44.25 @ 135 / 46.00 @ 045. What does the comparison of refractive and corneal astigmatism suggest?

Answer: There is approximately 0.25 D of against-the-rule lenticular astigmatism present

Corneal astigmatism from keratometry is 1.75 D axis 135 (steep at 045). The manifest refraction shows 1.25 D axis 045, meaning the refractive cylinder is less than the corneal cylinder by 0.50 D. Because the axes are orthogonal between K readings and the refraction convention, the lenticular component partially neutralizes corneal astigmatism. The net internal (lenticular) astigmatism is approximately 0.25–0.50 D against-the-rule, making option B the best clinical approximation.

During binocular indirect ophthalmoscopy, a clinician uses a 20D condensing lens and observes a retinal lesion. If the actual lesion diameter is 1.5 disc diameters and the observer's working distance is 50 cm, which statement best describes the aerial image characteristics?

Answer: The aerial image is real, inverted, and located between the condensing lens and the observer

In binocular indirect ophthalmoscopy, the condensing lens creates a real, inverted aerial image of the fundus that is suspended in space between the condensing lens and the observer. This is fundamentally different from direct ophthalmoscopy. The image appears inverted both top-to-bottom and left-to-right. A 20D lens provides less magnification (~3×) than a 28D lens (~2.3×) but a wider field of view.

A patient's Goldmann visual field shows a ring scotoma sparing fixation at approximately 20-30° eccentricity in both eyes. Automated perimetry confirms a mid-peripheral depression with preserved central and far-peripheral sensitivity. Which condition is MOST consistent with this pattern?

Answer: Retinitis pigmentosa with mid-peripheral photoreceptor degeneration

A ring scotoma at 20–30° eccentricity with preserved central (foveal) and far-peripheral sensitivity is the hallmark of retinitis pigmentosa (RP). RP causes progressive loss of rod photoreceptors beginning in the mid-periphery, producing this characteristic ring-shaped field defect. Glaucoma typically produces arcuate scotomas, nasal steps, or generalized depression. Hydroxychloroquine toxicity produces a paracentral or central ring scotoma closer to fixation (within 10°). Central serous chorioretinopathy causes a central scotoma, not a ring pattern.

When calibrating a Goldmann applanation tonometer, the correct procedure requires the drum to read 0 mmHg when the prism is placed against a calibration bar. If the instrument reads 1 mmHg with no load applied and 22 mmHg when the calibration weight (equivalent to 20 mmHg) is applied, which statement is accurate?

Answer: The tonometer is out of calibration and is over-reading by approximately 2 mmHg across the range

Acceptable calibration tolerance for the Goldmann tonometer is ±0.5 mmHg at 0 mmHg and ±1 mmHg at the 20 mmHg check point. Here the zero reads +1 mmHg (outside ±0.5 tolerance) and the 20 mmHg weight reads 22 mmHg (2 mmHg over, outside ±1 tolerance). The consistent +2 mmHg offset across both check points indicates the instrument is systematically over-reading — spring tension is too low (a stiffer spring would require more force, reading higher, but the tonometer over-reads IOP when the spring is under-tensioned, applying less applanation force). The device requires recalibration before clinical use.

A 34-year-old patient is being evaluated for contact lens fitting. Corneal topography reveals a best-fit sphere of 43.50 D centrally, significant inferior steepening of 2.80 D, and an I-S value of 3.1 D on the KISA% index calculation. Pachymetry shows a minimum thickness of 468 µm at a point displaced inferiorly. What is the MOST appropriate clinical conclusion?

Answer: Subclinical or early keratoconus — contact lens fitting should proceed only after informing the patient of progression risk

An I-S value >1.4 D, inferior steepening >1.5 D relative to the superior cornea, and minimum pachymetry <500 µm at an inferiorly displaced thinnest point are all diagnostic indicators of subclinical or forme fruste keratoconus. The KISA% index values above 60% are suspicious and above 100% are diagnostic. While contact lenses may still be fitted, the patient must be counseled about keratoconus progression risk, the need for serial topographic monitoring, and the contraindication to LASIK. Pellucid marginal degeneration shows inferior thinning with steepening above the thinning zone, a different topographic pattern.

A patient receives a 2% pilocarpine challenge as part of an Adie's tonic pupil workup. Thirty minutes after instillation, the affected pupil constricts markedly while the fellow pupil shows only minimal response. Which pharmacological principle explains this finding?

Answer: Denervation supersensitivity of the iris sphincter to cholinergic agents due to postganglionic ciliary ganglion damage

Adie's tonic pupil results from damage to the postganglionic parasympathetic neurons in the ciliary ganglion. Following postganglionic denervation, the effector organ (iris sphincter muscle) upregulates receptor density — a phenomenon called denervation supersensitivity (Cannon's law). As a result, even a dilute cholinergic agent like 0.1% pilocarpine (or in this case 2% in a supersensitive eye) produces exaggerated constriction of the denervated pupil compared to the normal fellow eye. This confirms the diagnosis of Adie's syndrome and localizes the lesion to the postganglionic parasympathetic pathway.