Sex Differences in Intraocular Pressure and Retinal Vessel Responses After Sustained Isometric Knee Extension in Young Adults: A Quasi-Experimental Study

Purpose: Evidence on the safety of single-joint isometric exercises of the lower legs remains limited. Thus, the aims of this study were to examine intraocular pressure (IOP) and retinal vessel responses during a 1 min isometric knee extension task and to assess potential sex-related differences. Materials and Methods: This prospective, parallel-group, quasi-experimental exploratory trial enrolled 43 healthy young adults (22 males and 21 females; age range: 19–35 years), who performed a 1 min sustained maximal-effort isometric knee extension task. The cardiovascular response, IOP, and retinal vessel diameters were assessed. Results: The isometric task increased fatigue, heart rate, systolic blood pressure (SBP), and mean arterial pressure in both sexes (p < 0.05), with males exhibiting a significantly greater rise in SBP than females (p < 0.05). A significant reduction in IOP was observed only in males (p < 0.05). Central retinal arteriolar equivalent decreased in both sexes (p < 0.05), whereas central retinal venular equivalent (CRVE) increased exclusively in females (p < 0.05). Despite the difference in the CRVE response, both sexes exhibited a comparably reduced arteriolar-to-venular diameter ratio (p < 0.05). Conclusions: To sum up, the isometric maximal-effort knee extension exercise increased cardiovascular loads in both sexes, with males showing a greater SBP rise and a reduction in IOP. Although retinal microvascular responses were sex specific, both sexes showed a similar reduction in the arteriolar-to-venular diameter ratio, indicating a consistent shift in microvascular regulation.