Optometry Flashcards

A patient presents with a cycloplegic refraction of −3.50 −1.25 × 090 OD. The manifest refraction shows −3.00 −1.00 × 090 OD. Which component of the difference is most likely attributable to residual accommodation rather than latent hyperopia?

Answer: The 0.50 D difference in spherical equivalent

Comparing cycloplegic to manifest refraction reveals latent hyperopia (or unmasked myopia reduction) through the spherical equivalent difference. Here, SE cycloplegic = −4.125 D vs manifest SE = −3.50 D — a 0.625 D difference. The cylinder difference is secondary and often reflects relaxation of accommodative-driven astigmatism, but the spherical equivalent captures the core accommodation-driven discrepancy. The 0.50 D sphere difference alone doesn't account for cylinder contribution to SE.

During Goldmann applanation tonometry, the mires appear oval rather than circular. What is the most likely cause and the appropriate corrective action?

Answer: The tonometer tip is misaligned rotationally; rotate the prism so the white line aligns with the patient's corneal astigmatic axis

Oval mires during GAT indicate the prism tip is not properly aligned with the patient's corneal astigmatic axis. For cylinders ≥3 D, the prism must be rotated so the red mark aligns 43° to the flatter meridian to minimize the effect of corneal astigmatism on the measurement. Excessive fluorescein causes thick, bright mires (not oval), and a dirty prism causes irregular rather than consistently oval rings.

A technician performing automated perimetry notices a patient's reliability indices show 28% fixation losses, 0% false positives, and 0% false negatives on a 24-2 SITA Standard field. How should this result be interpreted?

Answer: The field is unreliable due to high fixation losses and should be repeated after retraining the patient

Fixation losses >20% indicate the patient is not maintaining steady fixation on the central target, as the Heijl-Krakau method detected responses during blind spot presentations. While 0% false positives and negatives suggest the patient understood the task and wasn't trigger-happy or missing stimuli deliberately, the high fixation loss rate compromises spatial reliability — scotomas may appear shifted or artifacts introduced. Repeating after patient retraining is standard protocol. SITA does not internally correct for fixation errors.

When performing keratometry on a patient with 4.00 D of with-the-rule corneal astigmatism, the mires appear distorted and cannot be superimposed. What is the most appropriate next step?

Answer: Proceed to corneal topography, as manual keratometry is unreliable above approximately 3.50–4.00 D of irregular astigmatism

Manual Javal-Schiøtz or Bausch & Lomb keratometry assumes a spherocylindrical corneal surface with regular astigmatism. When mires are distorted and cannot be superimposed, it indicates irregular astigmatism or surface pathology (e.g., keratoconus, scarring, dry eye) that exceeds the instrument's assumptions. Corneal topography (Placido-based or Scheimpflug) maps the entire anterior surface and yields clinically useful data in these cases. Simply averaging readings introduces significant error.

A patient is dilated with 1% tropicamide and 2.5% phenylephrine for a routine exam. Thirty minutes post-dilation, the patient complains of palpitations and has a blood pressure of 172/98 mmHg. Which agent is the primary pharmacological suspect and why?

Answer: Phenylephrine, because it is an alpha-1 adrenergic agonist that causes peripheral vasoconstriction and reflex tachycardia or direct cardiovascular stimulation

Phenylephrine is a selective alpha-1 adrenergic agonist that causes systemic vasoconstriction when absorbed via the nasolacrimal duct or conjunctiva, leading to hypertension and reflex bradycardia, though paradoxical tachycardia can also occur. The 2.5% concentration is generally safer than 10%, but significant systemic absorption can still occur. Tropicamide (anticholinergic) can cause tachycardia but is not primarily associated with acute hypertensive episodes. Nasolacrimal occlusion post-instillation reduces systemic absorption.

Using the lensometer, a technician verifies a progressive addition lens (PAL) and finds the distance power is −1.25 −0.75 × 175, and the near addition measures +2.25 D. The reading power should be documented as:

Answer: The add of +2.25 is added to the sphere only, yielding a near Rx of +1.00 −0.75 × 175

For progressive lenses, the add power is added algebraically to the sphere component of the distance prescription only — the cylinder and axis remain unchanged. Distance Rx: −1.25 −0.75 × 175. Adding +2.25 to the sphere: −1.25 + 2.25 = +1.00. Near Rx = +1.00 −0.75 × 175. This is a frequently tested concept; the cylinder does not change in the reading zone of a PAL. Answer B is incorrect because it drops the cylinder, and D incorrectly replaces rather than adds to the sphere.