Visual performance is degraded by several optical phenomena including wavefront aberrations, light scattering, and diffraction.
Editor's Note: In the rapidly evolving subspecialty of refractive surgery, devices are being developed to help researchers and surgeons better understand the effect of aberrations on optical quality.
Karolinne Maia Rocha, MD, PhD, and Ronald Krueger, MD, MSE, are forging the way by developing clinical applications of a compact adaptive optics visual simulator that uses deformable mirrors to induce and manipulate aberrations for clinical applications. The clinician scientists are using this device to simulate and evaluate correction of highly aberrated eyes, in addition to expanding depth of focus with selective use of spherical aberration.
In the future, clinicians may have a device that allows patients not only to experience a correction prior to surgery, but also to customize it to their needs and preferences via simulation. -George O. Waring IV, MD
Effects of aberrations
After measuring ocular aberrations, we programmed the device to compensate for the eye's wavefront error up to the 4th order and successively applied different individual Zernike aberrations using a 5-mm pupil. The generated aberrations included defocus, astigmatism, coma, trefoil, and spherical aberration, at a level of 0.1, 0.3, and 0.9 µm. We assessed the VA through the adaptive optics system using computer-generated Landolt-C optotypes (Freiburg ACuity Test [FrACT]).
The adaptive optics correction of the aberrations present in the subjects' eyes (HOA correction) improved their VA by a mean of 1 line (–0.1 LogMAR), when compared with the best sphero-cylinder correction (BSCVA). The induced HOA in an amount of 0.1 µm RMS resulted in a limited decrease in VA (mean +0.05 LogMAR), while 0.3 µm RMS of Zernike aberrations induced visually significant acuity losses with a mean reduction of 1.5 lines (+0.15 LogMAR).
Larger aberrations with a magnitude of 0.9 µm RMS resulted in greater VA impairment that was more pronounced with spherical aberration (+0.64 LogMAR) and defocus (+0.62 LogMAR), while trefoil (+0.22 LogMAR) was found to be better tolerated. The correction of higher-order aberrations (custom wavefront corrections) improved the VA to a greater degree when compared with best-spectacle correction. The effect of relatively large single Zernike aberrations on VA strongly depended on the mode number, with lower azymuthal orders (e.g., defocus and spherical aberration) being more unfavorable to visual performance.1