COMT exam prep for your senior technicians

A right hypertropia is worse in left gaze and worse on left head tilt. A colleague charts it as a right superior oblique palsy. What does the third step actually show?

After the first two steps the candidates are the right superior oblique, acting in adduction, and the left superior rectus, acting in abduction. On left tilt the left eye must intort using its superior oblique and superior rectus; with the superior rectus weak, the unopposed superior oblique depresses the left eye and the right hypertropia grows. A right superior oblique palsy would grow on right tilt instead, so the chart entry does not match the observations. The right inferior rectus acts in right gaze and was excluded at the second step, and the tilt step applies whichever way the gaze step points.

A reliable field shows one deep paracentral scotoma of four adjacent points near fixation, and every other point is normal. Which pairing of global indices is most likely?

The mean deviation averages the whole field, so a few deep points among many normal ones barely move it, while the pattern standard deviation measures how irregular the field is and rises with a small deep defect. A markedly negative mean deviation with a normal PSD is the signature of diffuse depression such as media opacity. Both indices abnormal fits widespread focal loss, and a normal PSD would ignore the irregularity the scotoma creates.

Before an angiogram, a patient says his skin broke out in hives after a dye study years ago, and that he has asthma. What does the photographer do with this?

The label notes that reactions are more frequent in patients with a prior reaction other than nausea and vomiting, or with a history of allergy or asthma, so both facts go to the physician before the dye is prepared. Proceeding without telling anyone ignores exactly the history the screening is for. Changing the test and giving medication are physician decisions.

Sitting at 67 cm with no lens of any kind before the eye, you see the reflex fill the pupil with no motion in every meridian. What is this eye's refractive error?

Neutrality means the eye's far point sits at the examiner's peephole, and a far point 67 cm in front of the eye belongs to a myope of about 1.50 D. An emmetrope's far point is at infinity, so plano would show with motion at this distance and need +1.50 to neutralize. The plus figure reverses the sign of the working-distance correction. The dioptric value of 67 cm is 1 divided by 0.67, about 1.50 D, rather than 0.67 D.

A pair ordered with no prism reads 2 prism diopters base in at the right pupil mark and 2 prism diopters base out at the left. What does that do to the patient's horizontal vergence demand?

Base in before the right eye and base out before the left displace both images toward the patient's right, so the prism is yoked and creates no net convergence or divergence demand. It is still unordered prism, shifting the whole scene sideways, and it is recorded and reported. Totaling the two as 4 prism diopters treats opposite-side bases as if they worked together, and assigning the demand to one lens ignores the other.