The effect of continuous strenuous exercise on intraocular pressure.

The effect of a continuous 110-km march with a 20-kg backpack load on intraocular pressure (IOP), plasma osmolarity, blood lactate, pH, and other related laboratory parameters was studied in 22 healthy young volunteers. Intraocular pressure decreased significantly at all marching intervals and returned to baseline level 3 hr after the completion of marching. The maximal average reduction during marching was 4.1 mmHg, 26.5% below the baseline level. The IOP decreased again 48 hr after the march and returned to baseline level 48 hr later. There were two peaks of increased plasma osmolarity (one during the march and the other 48 hr after the march). There was no correlation between IOP changes and levels of pH, blood lactate, serum proteins, and electrolytes or hematologic parameters. These findings suggest that IOP reduction is related inversely to plasma osmolarity during and after strenuous exercise.