Purpose: To evaluate the depth of focus induced by controlled amounts of negative spherical aberration (SA) in patients implanted bilaterally with light adjustable intraocular lenses (LALs). The impact of binocular summation and combinations of defocus and SA will be specifically addressed.
Methods: Twelve cataract patients were implanted bilaterally with LALs (Calhoun Vision, Pasadena, USA). Two weeks after surgery, the implanted lenses were irradiated with appropriate spatial intensity profiles to correct the patients’ defocus and astigmatism. Patients received a second aspheric light adjustment to induce controlled amounts of negative spherical aberration. After the adjustment procedures, two photo-locking treatments were performed to ensure that the LAL was fixed. The surgery and the light treatments were performed first in one eye set for emmetropia and neutral SA and a few weeks later on the fellow eye where negative SA was induced. Wavefront-guided refraction was determined for every eye during the entire adjustment process. High order aberrations, and in particular SA, were measured with a Hartmann-Shack sensor before and after each light treatment. Visual acuity (VA) was measured using a computer-assisted procedure both monocularly (each eye separately) and binocularly. All the VA measurements were performed for letters projected on a microdisplay placed at 10 m, 60 cm, 40 cm and 30 cm.
Results: In the eyes with aspheric treatments, the measured SA was negative, ranging between -0.05 and -0.2 microns for a 4-mm pupil. For the eye without aspheric treatment, the monocular uncorrected distance VA was on average 1.1 for distance, decreasing to around 0.4 at 30 cm. In the eyes with low values of induced SA (less than -0.1), distance VA was around 0.9, increasing to 1.1 for intermediate distance (60 cm), and decreasing to 0.7 and 0.50 for near distances of 40 and 30 cm, respectively. In the eyes with larger induced SA, distance VA was reduced to around 0.8; however, they also displayed a concomitant increase for both the intermediate and near distances with VAs of 0.9 at both 60 and 40 cm and 0.8 at 30 cm. The measured binocular VA was on average 1.1 for 10 m and 0.8 for 40 cm.
Conclusions: The use of LALs to produce extended depth of focus by modifying the eye’s spherical aberration was demonstrated. The particular amounts of spherical aberration and defocus can be customized to maximize quality of vision at all distances by using binocular summation mechanisms.