Purpose: To design and validate a standard, simple, and reliable iris color classification and to study its distribution in a Spanish population. Iris color has a geographic distribution and has been correlated with different ocular diseases. However, there is no standard and validated iris color classification allowing comparison among different studies.

Methods: Classification was made in three grades (blue-gray, hazel-green, brown) and was validated by 3 independent readers. Initially, a preliminary study was made in 50 iris photographs to detect technical hitches. Afterwards, based on this procedure, 221 iris photographs were graded.

Results: Measures of interobserver reliability were 0.786 by kappa index with an agreement of 89.6%.Iris color distribution in the Spanish cohort was blue-grey 16.29%, hazel-green 55.2%, and brown 28.5%.

Conclusions: This classification is simple, reliable, and easy to use in clinical research and by ophthalmologists or generalists in practice. The Spanish cohort from this study shows a different iris color distribution from those previously published in other countries.