The existence of the retinohypothalamic pathway suggests that light may influence autonomic outflow activity. The objective of this study was to examine the correlation between the estimated iris muscle sympathetic-parasympathetic area (IRIS) ratio and the sympathetic?parasympathetic ratio (Low Frequency (LF)/High Frequency (HF) ratio). The study population consisted of 200 females and 200 males (mean age, 32.4 ± 7.1 y). The IRIS ratio was determined from digital photographs of the iris in a computer setting. The LF/HF ratio was determined from records of heart rate variability obtained using a Holter implementation. The minimum LF/HF ratio was 1.4 and the maximum 5.6 (mean, 3.0 ± 0.8). The minimum IRIS ratio was 1.4 and the maximum 4.9 (mean, 2.7 ± 0.6). A strong positive correlation was determined between the LF/HF and IRIS ratios in the entire population (r=0.825; p<0.001) and positive correlations were also observed in males and females separately. The intraclass correlation between the LF/HF and IRIS ratios was 0.836. A strong correlation exists between the LF/HF and IRIS ratios.