Validity and interpretation of Amsler grid reports
R. A. Schuchard
Lions Vision Center, Wilmer Institute, Johns Hopkins University School of Medicine, Baltimore, Md.
OBJECTIVE--To compare the reports of scotomas and metamorphosia in standard
and threshold Amsler grid testing with the location and extent of scotomas
in the macular region as determined by standard and threshold fundus
perimetry. DESIGN--Fundus perimetry determined the existence, size, and
retinal location of macular scotomas. Amsler grid testing was performed
with the scanning laser ophthalmoscope and the TA-300 system (Stereo
Optical, Chicago, Ill). All testing was done at both standard and threshold
light conditions. PATIENTS--Fifty-five patients with vision loss in the
macular region and 10 normally sighted subjects. RESULTS--Nearly half of
the standard and threshold scotomas were not detected by Amsler grid
testing. For scotomas of 6 degrees or less in diameter, 77% of standard and
87% of threshold scotomas were not detected by Amsler grid testing. Of the
eyes with central scotomas involving the fovea, 66% used an eccentric
preferred retinal locus for fixating the center of the grid. Finally, more
than half of the distortion reported in Amsler grids was at the retinal
area that corresponded to the scotoma area, not a nonscotoma retinal area.
CONCLUSION--Amsler grid reports have poor validity and cannot be accurately
interpreted for use in the clinical diagnosis of retinal defects.
