Altered visual sensitivity in axial high myopia: a local postreceptoral phenomenon?
OBJECTIVE
The present study investigated retinal integrity in high myopia using spatial psychophysical tasks.


METHODS
Ten axial high myopes (-8.5 to -11.5 D) and 10 age-matched control subjects (+/-1.0 D) were recruited. All participants underwent clinical examination and ocular biometry and demonstrated no visible macular disease with visual acuities better than 6/12. Foveal summation thresholds were determined for white and S-cone-isolating spots of various diameters up to 5.4 degrees and spatial contrast sensitivity to luminance sine wave gratings (0.5-9.7 cyc/deg). Data were analyzed after correction for the magnification induced by eye size and correcting lens power.


RESULTS
Spatial summation for both white and S-cone-isolating spots showed a generalized loss of sensitivity at all spot sizes in myopes relative to control subjects (P = 0.01). Critical areas at maximum summation were significantly larger in myopes, for S-cone isolating spots only, after image size correction (P = 0.048). Sensitivity at maximum summation correlated negatively with vitreous chamber depth for both targets (P = 0.005). Sensitivities for S-cone and luminance spots also correlated (P < 0.001), indicating widespread dysfunction. Myopes displayed contrast sensitivity losses at high spatial frequencies (P </= 0.006) with a normal peak contrast sensitivity.


CONCLUSIONS
These data can be interpreted to indicate that highly myopic eyes have either (1) a reduction in the number of receptors and/or a reduction in their sensitivity or, (2) a reduction in the sensitivity of postreceptoral processes. The presence of normal contrast sensitivity at low spatial frequencies indicates dysfunction at a postreceptoral level in high myopes.
Jaworski
Alexandra
A
Department of Optometry and Vision Sciences, The University of Melbourne, Victoria, Australia.
Gentle
Alex
A
Zele
Andrew J
AJ
Vingrys
Algis J
AJ
McBrien
Neville A
NA
D000293:Adolescent; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005123:Eye / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D010786:Photoreceptor Cells / Q000503:physiopathology*; D014463:Ultrasonography; D014792:Visual Acuity / Q000502:physiology; D014822:Vitreous Body / Q000503:physiopathology