Fluorometry of the crystalline lens for correcting blue-on-yellow perimetry results

Optical and neural sources of short wavelength sensitivity should be separated in the assessment of the results of blue-on-yellow (B/Y) perimetry. It has been shown previously that lens autofluorescence is related directly to lens yellowing and age. The aim of this study was to find out if B/Y perimetry results can be better corrected by using lens fluorometry than by age.

The authors evaluated one randomly chosen eye of 40 normal subjects and 39 age-matched patients with ocular hypertension and different stages of glaucoma. The authors obtained the mean sensitivity (MS) of the 24-2 B/Y visual fields with a Humphrey perimeter and determined the lens transmission index (LTI) from the ratio between posterior and anterior autofluorescence peaks measured with their fluorometer. A multiple regression analysis was used to evaluate the variability of the B/Y MS by age and LTI in normal subjects.

The authors found a statistically highly significant linear correlation of B/Y MS to LTI in healthy subjects (R = 0.83; P < 0.0001). The 95% prediction interval of the normal subjects was determined. The majority of the MS values of the ocular hypertensives were inside the prediction limits, whereas approximately half of the patients (4 of 9) with early glaucoma and the majority of patients (14 of 15) with moderate and advanced glaucoma were below the prediction interval. The residual standard deviation of the B/Y MS with age alone was larger than that with LTI alone in the model (3.66 dB and 3.22 dB, respectively).

The interindividual variation of the lens transmission properties increases with age. The reference level for correcting B/Y perimetry results can be determined more precisely using fluorometry of the lens than with age alone.