<p>To investigate changes in the pupil size and accommodation following prophylactic peripheral laser retinopexy (PPLR). This prospective self-controlled study enrolled patients who underwent unilateral PPLR. The photopic and mesopic pupil diameters (PPD and MPD), accommodative amplitude (AA), and central corneal sensation (CCS) were measured at baseline and 1 week, 1 month, and 3 months post-PPLR in both the treated eye and the untreated fellow eye. Standard ophthalmic examinations were also performed at each follow-up visit. Longitudinal changes were analysed by using baseline-adjusted linear mixed-effects models comparing the treated and fellow eye over time. Associations between pupillary or accommodative changes and baseline characteristics were evaluated with multivariable regression. A total of 98 patients (98 treated and 98 fellow eyes) were analysis. Both the PPD and MPD increased significantly at 1 week post-PPLR compared with those at baseline. By 1 month, the dilation of the PPD and MPD had decreased but remained significant. At 3 months, neither the PPD nor the MPD significantly differed from baseline at the group level. A higher laser dose was strongly associated with the development of pupil dilation. Compared with that at baseline, the AA in the treated eyes significantly decreased at 1 week and 1 month after PPLR, with the difference no longer reaching statistical significance at 3 months. No significant differences in CCS were detected at any follow-up visit. PPLR resulted in significant but transient increases in the PPD and MPD, along with a temporary reduction in accommodation. A higher number of laser spots was significantly associated with postoperative pupil dilation. These potential effects should be discussed with patients prior to treatment, particularly with those scheduled for refractive surgery.</p>