EFFECTIVE APPROACH

Average values of monocular visual acuity at different distances after lens adjustments. Courtesy of Eloy A Villegas PhD, Laboratorio de Óptica, University of Murcia

Implantation of the light adjustable lens (LAL, Calhoun Vision) with adjustment to customise depth of focus shows promise as an effective approach for presbyopia correction after cataract surgery in patients with a history of myopic LASIK, reported Eloy A Villegas PhD at the XXXIII Congress of the ESCRS in Barcelona, Spain.

Dr Villegas reported outcomes for six post-myopic LASIK eyes comprising two small subgroups classified and treated based on the initial magnitude of their positive spherical aberration (SA) and depth of focus. Following customised irradiation of the LAL, they achieved mean visual acuity (VA) of about 20/22 at far, 20/20 at intermediate, and 20/26 (J2) at near.

“We recently reported that in cataract patients implanted with the LAL, controlled induction of negative SA extends the depth of focus and improves near vision (Villegas EA et al. Am J Ophthalmol. 2014;157(1):142-9). However, post-myopic LASIK patients present a special challenge. As the refractive surgery can induce positive SA, these patients may present with high and variable SA,” said Dr Villegas, Associate Professor of Optics, University of Murcia, Spain.

“Our approach using the LAL takes the variability in SA into account and customises depth of focus both in terms of the range and power position by adjusting both refraction and SA to achieve optimal visual outcomes,” he added.

DETERMINING THE TARGETS

Patients were assessed at about two weeks after cataract extraction and LAL implantation with measurements of refraction, SA, depth of focus, and pupil diameter. Through-focus VA was measured using trial lenses, and a depth of focus curve was fitted using a normalised three-parameter Gaussian function. A depth of focus parameter was estimated as the dioptric power range providing decimal VA of 0.8 or better.

Then, the LALs were irradiated with appropriate light profiles to adjust the SA and refraction in order to optimise depth of focus and the quality of near vision. Myopic shift of best focus was customised in all eyes in order to optimise the depth of focus position according to the visual needs of each patient.

The two subgroups of post-LASIK eyes consisted of one cohort of four eyes with high positive SA (>+0.3μm and pupil diameter of 3mm), and the second cohort included two eyes with low positive SA (0.05μm to 0.15μm and pupil diameter of 4 to 5mm). Depth of focus averaged 3.1D (range 2.1 to 4.0D) for the eyes with high positive SA and was 1.5D and 1.7 D, respectively, for the two eyes with low positive SA.

“Since the depth of focus was already good in the eyes with high positive SA, our target with the light customisation was to adjust the optimal position of the depth of focus. In contrast, the aim of the light adjustment in the eyes with low positive SA and lower depth of focus was to induce negative SA in order to increase their depth of focus,” Dr Villegas explained.

MYOPIC SHIFT

The customisation goals were achieved. Mean depth of focus remained 3.1D in the eyes with high positive SA. In the eyes with low positive SA, mean SA was -0.10μm after the customisation procedure and depth of focus increased to 2.5D and 3.0D, respectively, in the
two eyes.

A mean myopic shift of -0.6D was induced in the eyes with high positive SA and of -1.34D in the eyes with low positive SA. “With this myopic shift we were able to increase VA at near and intermediate distances while maintaining good VA outcomes at far distance,” Dr Villegas added.

As a comparison, he showed functional data for a control group of five eyes that had no history of LASIK, low positive SA (0.05 to 0.15μm and pupil diameters of 4.0 to 5.0mm), and a mean depth of focus of 1.9D. While their mean VA was excellent at far distance (20/20), it was about 20/35 at intermediate, and J10 (20/100) at near.

Eloy A Villegas: villegas@um.es