Purpose To determine whether altered eating habits and periods, especially the pre-dawn meal, during Ramadan fasting have any significant effect on intraocular pressure (IOP), tear secretion, corneal and anterior chamber parameters.Methods IOP, basal tear secretion (BTS), reflex tear secretion (RTS), and Pentacam measurements of 31 healthy volunteers were performed at 0800 and 1600 hours during Ramadan fasting and 1 month later during non-fasting period.Results Comparison of measurements between fasting and non-fasting periods at 0800 hours revealed significantly higher values for IOP (P = 0.005), RTS (P = 0.006), and BTS (P = 0.014) during fasting. Conversely at 1600 hours, IOP was significantly lower during fasting (P = 0.013) and no statistically significant difference was noted for RTS and BTS. IOP showed a diurnal variation of 2.45 mmHg (P ≤ 0.001) and BTS showed a 3.06 mm decrease (P = 0.04) during the fasting period. No significant differences could be found in the corneal and anterior chamber parameters during fasting and non-fasting periods.Conclusions Our results revealed that fluid loading at the pre-dawn meal during Ramadan fasting might increase the IOP and tear secretion in the early morning period and these values decrease remarkably at the end of 12 h of fasting due to dehydration. © 2010 Macmillan Publishers Limited All rights reserved.