BY Gregory DeNaeyera, Donald R. Sanders, Timothy S. Farajianc
To determine surface coverage of measurements using the sMap3D corneo-scleral topographer in patients presenting for scleral lens fitting.
Twenty-five eyes of 23 scleral lens patients were examined. Up-gaze, straight-gaze, and down- gaze positions of each eye were “stitched” into a single map. The percentage surface coverage between 10 mm and 20 mm diameter circles from corneal center was compared between the straight-gaze and stitched images. Scleral toricity magnitude was calculated at 100% coverage and at the same diameter after 50% of the data was removed.
At a 10 mm diameter from corneal center, the straight-gaze and stitched images both had 100% coverage. At the 14, 15, 16, 18 and 20 mm diameters, the straight-gaze image only covered 68%, 53%, 39%, 18%, and 6% of the ocular surface diameters while the stitched image covered 98%, 96%, 93%, 75%, and 32% respectively. In the case showing the most scleral coverage at 16 mm (straight-gaze), there was only 75% coverage (straight-gaze) compared to 100% (stitched image); the case with the least coverage had 7% (straight gaze) and 92% (stitched image). The 95% limits of agreement between the 50% and 100% coverage scleral toricity was between 1.4D (50% coverage value larger) and 1.2D (100% coverage larger), a 2.6D spread. The absolute difference between 50% to 100% coverage scleral toricity was ≥0.50D in 28% and ≥1.0D in 16% of cases.
It appears that a single straight-gaze image would introduce significant measurement inaccuracy in fitting scleral lenses using the sMap3D while a 3-gaze stitched image would not.