Foveal cone densitometry in high myopia

We performed foveal cone densitometry using a modified fundus camera in 17 eyes of 17 normal subjects (age range, 20 to 47 yr, refractive error, + 2.0 to -2.5 D) and 15 eyes of 15 high myopia subjects with normal visual acuity (age range, 18 to 46 yr, refractive error, -9.0 to -14.5 D). After fully bleaching, the density of photopigment was measured for 7 minutes by a test spot of 562 nm in wavelength and 1 degree in diameter, focussed on the fovea. Two-way density and the time constant of pigment regeneration were calculated. No significant difference was found in two-way density between the two groups. The time constant in high myopia (161.6 ± 36.6 sec), however, was significantly increased (p<0.01), compared with normals (124.0±28.7 sec). To study the correlation of psychophysical visual function, we performed a photostress recovery test, which revealed a significant delay of the recovery time in high myopia (p<0.01). These results suggest that a delay in foveal cone pigment kinetics precedes loss of cone cells or chorioretinal degeneration in high myopia.