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Assessment of the ocular media absorption index
Purpose:
To determine a practical method for quantifying in vivo lens absorption by human crystalline, obtaining an index of lens density in our population.
Method:
62 normal subjects were evaluated in this study (ages ranging from 20 to 71 years). TESTING PROCEDURE: Measurements of dark-adapted scotopic thresholds for 450 nm and 656 nm stimuli were obtained (Tubinger perimeter) in order to determine ocular media absorption. Van Norren and Vos's procedure was used to calculate ocular media absorption transmission loss. Least-squares linear regressions were used to correlate lens density to age.
Results:
A gradual and approximately linear increase in average lens absorbance was found under 55 years of age. Elder subjects showed a higher increase in this absorbance with higher variability. A correction factor for age-related ocular media absorption was obtained from the calculated curve. The range was approximately 1 to 5 dB.
Conclusion:
Determination of the transmission characteristics of the preretinal media is essential for interpreting threshold sensitivity values. Increase in lens absorption has been shown to be selective for short wavelengths. Due to this fact, a correction factor for the age-related ocular media absorption should be applied to avoid misinterpretation of the Blue-on-Yellow perimetry absolute results. That factor may discriminate sensitivity losses due to changes in the lens from those due to retinal or neuronal dysfunction.