Objective: To investigate the association between cardiorespiratory fitness and mean corrected intraocular pressure (IOP) in a normotensive health check-up population, and to evaluate potential differences across age and sex strata.

Methods: This cross-sectional study consecutively enrolled adults aged 18-70 years who completed cardiorespiratory fitness testing and ophthalmologic examinations at the Health Management Center of Sichuan Provincial People's Hospital between July 1, 2019 and December 31, 2025. Individuals were excluded if they had a history of glaucoma, ocular diseases interfering with IOP measurement, systemic diseases or medications affecting IOP, contraindications to fitness testing, or abnormal blood pressure. A final sample of 2,921 normotensive individuals was included. Cardiorespiratory fitness was assessed by estimated maximal oxygen uptake (VO₂max). After age- and sex-stratified grouping, low cardiorespiratory fitness was used as the reference, and the remainder were defined as the moderate-to-high cardiorespiratory fitness group. The primary outcome was the mean corrected IOP of both eyes. Multiple imputation, multivariable linear regression, and age- and sex-stratified analyses were used to evaluate the association.

Inclusion Criteria:

1. Age 18-70 years;
2. Ability to complete standardized cardiorespiratory fitness testing and provide valid data; and
3. Ability to cooperate with a comprehensive ophthalmologic examination.

Exclusion Criteria:

1. Any history of glaucoma or ocular hypertension, or detection of glaucoma suspect signs such as cup-to-disc ratio ≥0.7, interocular cup-to-disc ratio asymmetry >0.2, or localized retinal nerve fiber layer defects;
2. Ocular diseases or surgical history affecting IOP measurement or optic nerve head assessment, such as corneal disease, uveitis, intraocular surgery, high myopia (spherical equivalent ≤ -6.00 D), or other optic nerve/retinal diseases;
3. Systemic diseases that could significantly interfere with IOP, optic nerve blood supply, or cardiorespiratory function, such as uncontrolled diabetes mellitus, severe cardiovascular or cerebrovascular disease, or chronic obstructive pulmonary disease;
4. Current use of topical or systemic medications known to affect IOP, including IOP-lowering eyedrops, systemic beta-blockers, or glucocorticoids;
5. Contraindications to cardiorespiratory fitness testing, such as severe musculoskeletal disorders or uncontrolled arrhythmias;
6. A documented history of hypertension, current use of antihypertensive medications, or abnormal blood pressure on a single measurement that did not normalize on re-examination (systolic blood pressure [SBP] ≥140 mmHg or diastolic blood pressure [DBP] ≥90 mmHg); and
7. Missing key study variables that precluded further analysis.

This single-center cross-sectional study enrolled adults who underwent health check-ups, completed standardized cardiorespiratory fitness testing, and underwent ophthalmologic examinations at the Health Management Center of Sichuan Provincial People's Hospital from July 1, 2019 to December 31, 2025. After applying the predefined inclusion and exclusion criteria, 2,921 normotensive adults were included in the final analysis.