Mechanism of exercise-induced ocular hypotension.
OBJECTIVE
Although acute dynamic exercise reduces intraocular pressure (IOP), the factors that provoke this response remain ill-defined. To determine whether changes in colloid osmotic pressure (COP) cause the IOP changes during exercise, standardized exercise was performed after dehydration and hydration with isosmotic fluid.


METHODS
Progressive cycle ergometer exercise to volitional exhaustion was performed after 4 hours' dehydration, and after hydration with 946 ml isosmotic liquid (345 mOsM). In each experiment, venous blood taken before and immediately after exercise was analyzed for hematocrit, plasma protein concentration, total plasma osmolality, and plasma COP.


RESULTS
Exercise in both experiments significantly reduced IOP and elevated COP (each P < 0.01). Dehydration, compared with hydration, also significantly reduced IOP and elevated COP, when measured before and after exercise (P < 0.05). The correlation of mean IOP with mean COP, over the entire range created by varying exercise and hydration statuses, was statistically significant (r = -0.99; P < 0.001). In contrast, other indexes of hydration status, including hematocrit, total plasma osmolality, and plasma protein concentration, failed to change as IOP changed and failed to correlate with IOP, on either a group or individual basis, in conditions of varying levels of exercise and hydration.


CONCLUSIONS
Acute dynamic exercise and isosmotic fluid ingestion each seem to change IOP through changes in COP.
Martin
B
B
Medical Sciences Program, Indiana University School of Medicine, Bloomington, USA.
Harris
A
A
Hammel
T
T
Malinovsky
V
V
D001798:Blood Proteins / Q000032:analysis; D001834:Body Water / Q000378:metabolism; D016552:Ergometry; D015444:Exercise; D006400:Hematocrit; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D009798:Ocular Hypertension / Q000097:blood / Q000209:etiology* / Q000503:physiopathology*; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D014883:Water-Electrolyte Imbalance / Q000503:physiopathology
D001798:Blood Proteins