BACKGROUND Fasting evidently influences a variety of physiological parameters that can impact the ocular system. Among these modifications are alterations in insulin secretion, sympathetic activity, free fatty acids, lipid profile, melatonin, cortisol, electrolytes and catecholamines. In this study, we investigated the possible alterations in intraocular pressure (IOP), visual acuity and refractive errors during Ramadan fasting. METHODS IOP, visual acuity and refractive errors of both eyes of volunteers were measured on the first and last days of Ramadan (once in the morning and evening). Body weight was measured so as to estimate the amount of dehydration. Data from the two examinations was analysed using one-way analysis of variance. A p-value of less than 0.05 was considered statistically significant. RESULTS 58 healthy, fasting male volunteers with a mean age of 40.7 +/- 7.1 years participated in the study. Statistical analysis demonstrated no difference in IOP, visual acuity or refractive errors on the first and last days of Ramadan, or within a single day (from morning to evening). CONCLUSIONS Our results reveal that Islamic Ramadan fasting does not profoundly affect physiological IOP, refractive error or visual acuity values in healthy volunteers. However, more detailed investigations using animal models should be designed to evaluate whether fasting has a pivotal influence on pathological conditions.