Objective: To evaluate the effects of religious fasting on tear secretion, tear osmolarity, corneal topography, and ocular aberrations. Methods: This prospective controlled study comprised 29 eyes of 29 healthy men. Before ophthalmologic examination, all subjects underwent corneal topography by a placido disc corneal topography and aberrometry device (OPD Scan II). Tear osmolarity was measured using OcuSense TearLab osmometer. Ocular surface disease index (OSDI) scores, tear break-up time (BUT), Schirmer I test, and lissamine green staining were evaluated. The measurements taken before and during Ramadan at the same hours between 4.00 and 5.00 PM were compared using paired sample t test, and a P value less than 0.05 was accepted as statistically significant. Results: The mean age of the study group was 27.8±5.9 years (range, 20-47 years). The mean tear osmolarity values were measured as 285. ±68.2 mOsm/L and 293.3±16.0 mOsm/L, whereas the mean Schirmer I values were 14.866.0 mm and 10.6±5.3 mm in nonfasting and fasting periods, respectively. Tear osmolarity, OSDI, and Oxford grading scores significantly increased (P=0.02, P=0.002, P=0.003, respectively), whereas Schirmer I values and intraocular pressure decreased (both, P < 0.001) during the fasting period compared with the nonfasting period. There were no significant differences in tear BUT, keratometry values, and corneal aberration measurements between nonfasting and fasting periods (P>0.05, for all). Conclusion: Fasting significantly decreases tear production and increases tear osmolarity; however, it does not deteriorate corneal topographic parameters and ocular aberrations in healthy subjects.