Purpose: : Rapid and accurate measurements are important when studying the eye’s peripheral optics. In the quest for a standard peripheral refraction instrument, we compared two prototype instruments, the EyeMapper (EM, Brien Holden Vision Institute, Sydney) and the Hartmann-Shack Scanner (SHS, Laboratorio de Optica, Murcia); both based on the Hartmann-Shack principle.
Methods: : The EM is a closed-view instrument permitting rapid scans (<0.5s) from +50° (nasal) to -50° (temporal) in 10° steps by means of a deflection system and scanning mirror. The SHS is an open-view instrument that records continuously (1° steps) from +40° to -40°. This is achieved using measuring optics attached to an L-shaped arm that sweeps quickly (<2s) across the eye. Data from the instruments were calibrated for different wavelengths (EM: 555nm, SHS:780nm). 25 subjects (age 33.8±12.3 yrs) with central spherical equivalentsranging from +1.50 to -4.00D (-1.96D±1.32D) were measured (5 independent repeats) in both eyes. The non-measured eye was occluded. Order of instruments and eyes was randomized. Power vector components M, J180 and J45 were analyzed (4mm pupil) for the common visual field (VF) angles measured.
Results: : In general measurements with the SHS were more positive in M across the VF (0.76D±0.23D, p<0.05). For relative peripheral refraction (RPR) of M agreement was good except near the blind spot (-10°/-20°) and in the far periphery (+40°). RPR of M was significantly different (p<0.05) between the instruments for both eyes at -10° (ODΔ=0.10D, OSΔ=0.22D), -20° (ODΔ=0.46D, OSΔ=0.18D) and +40° (ODΔ=0.60D, OSΔ=0.46D). All other VF angles showed no differences in M (p>0.05). RPR for J180 was significantly greater for all VF angles (p<0.05, average Δ=0.37D) with the EM. The difference in RPR for J45 was on average 0.05D. At -30°, +10° and +20° the difference in J45 was significant (p<0.05). Variability increased with VF angle for both instruments; on average being 0.31D and 0.39D for M, 0.21D and 0.20D for J180 and 0.28D and 0.23D for J45, for the EM and the SHS respectively.
Conclusions: : Overall, the new instruments agreed well in their RPRs and demonstrated low within-subject SD. Differences across the VF could be explained by different wavelengths used. The small differences found for RPR of J180 might be due to differences in instrument design and data processing. Further work assessing peripheral higher-order aberrations is underway.
Clinical Trial: : http://www.anzctr.org.au ACTRN12611001103954