Endocrine Abstracts

Rationale: A history of optic chiasm compression in patients treated for sellar tumors is associated with alterations in sleep-wake rhythm. The optic chiasm contains axons of intrinsically photosensitive retinal ganglion cells (ipRGCs) that mediate photoentrainment of the suprachiasmatic nucleus. Compression could disrupt this entrainment leading to desynchronization with the 24-hour light-dark cycle. The post-illumination pupil response (PIPR) after blue light exposure is a unique indicator of ipRGC function. PIPR measurement presents a promising tool to evaluate ipRGC impairment due to compression of the optic chiasm. This study is the first to compare the PIPR between pituitary patients with and without a history of chiasm compression.

Methods: Adult patients with at least one centrally impaired endocrine axis and normal ocular health were eligible for inclusion. Patients in the chiasm compression group all had visual field defects prior to treatment. Groups were matched for age, gender and BMI. The PIPR was assessed using a validated chromatic pupillometry protocol of five 5-minute blocks, ensuring reliable pupil measurements. The primary outcome parameters were defined as the absolute (PIPR-mm) and the relative (PIPR-%) difference between baseline and post-blue-stimulus pupil diameter averaged over the 2nd-4th minute of the corresponding block. For sufficient power, 25 patients were included in each group.

Results: For this analysis, pupillometry results of 23 patients in the chiasm compression group (CC+) and 22 patients in the control group (CC−) were available. Groups did not differ in relevant clinical characteristics or in baseline pupil diameter. No significant differences were found in PIPR-mm (mean±SD, CC+1.70±0.74mm and CC− 2.14±0.88mm; P=0.07) and PIPR-% (CC+36.80±10.97% and CC− 41.62±9.24%; P=0.12). On further examination of the normalized (i.e. relative to baseline) pupil diameter data, a less sustained PIPR in the CC+ group was observed. The difference in PIPR-% reached significance during the last minute of the post-blue block (CC+32.23±12.34% and CC− 40.87±8.23%; P=0.009), suggesting at least partial impairment of ipRGC function.

Conclusion: These preliminary results do not show significant differences in our primary PIPR outcomes. However, a less sustained PIPR was demonstrated in the CC+ group, which might correspond to less robust ipRGC transduction. The study identifies the PIPR as a potential tool to evaluate dysfunction of ipRGCs in patients with optic chiasm compression.