ADVANCED ASPHERIC MONOVISION

Secondary aspheric treatment of the Light Adjustable Lens (LAL, Calhoun Vision) to create an optimised form of monovision provides patients with excellent visual acuity for most distances and allows for spectacle independence, reported Pablo Artal PhD, at the XXIX Congress of the ESCRS.

The procedure has been dubbed “advanced aspheric monovision†to distinguish it from standard monovision, which is based on inter-eye differences in refraction. It involves bilateral implantation of the LAL. The dominant eye is treated for near emmetropia and zero spherical aberration (SA) to optimise distance vision. The non-dominant eye is made to be slightly myopic and to have some negative SA that results in increased depth of focus and enables good uncorrected near vision.

Dr Artal presented results from the first 14 patients treated with advanced aspheric monovision. All of the surgeries and light treatments were done by Jose Maria Marín MD, Department of Ophthalmology, Hospital Virgen de la Arrixaca, Murcia, Spain.

Measurement of refraction and spherical aberration to guide the light adjustment procedures was performed using a Hartmann-Shack wavefront sensor. Post-adjustment, SA measured with a 4.0mm pupil in the aspheric eyes ranged from -0.05 to -0.2 microns, and the results also showed good precision (±0.05 microns) in achieving the SA target.

UCVA testing was performed using a computer-assisted procedure with letters projected on a microdisplay placed at 10m, 60cm, 40cm, and 30cm. The monocular data showed good vision for distance in the dominant eyes as well as across the near and intermediate range for the non-dominant eyes, and the binocular results showed a summation effect such that binocular UCVA for all distances was equal to or slightly better than that of the better monocular result.

Spectacle independence

Considering a subgroup of four patients with -0.1 to -0.2 microns of SA in the aspheric eye, 100 per cent had simultaneous UCVA better than 20/20 at 10m, J1 or better at 60 and 40cm, and J2 or better at 30cm, reported Dr Artal, professor of physics and founder and director of the Optics Laboratory, University of Murcia, Spain.

“Achieving perfect refractive outcomes was the primary goal for creating the LAL. However, the LAL technology also allows options for manipulating the optics so that it can provide good quality near vision for spectacle independence. In fact, many of the patients in this early series became spectacle independent, and we think these are very promising results,†he said.

However, even better outcomes may be achieved in the future by taking advantage of the customisation feature of the procedure, Dr Artal told EuroTimes.

“In this study, patients were treated to achieve a specific amount of negative SA in each eye based on a target range we determined in a previous study using adaptive optics. However, this earlier research was done in normal subjects and not in patients,†he explained.

“In the near future, the target could be fully customised for each patient based on pre-treatment evaluation with an adaptive optics visual analyzer. Inducing SA specific to each patient would surely be an extremely powerful approach for providing the best quality vision and achieving optimum satisfaction.â€

In performing advanced aspheric monovision, the LAL is implanted in the conventional manner with about a two-week waiting period before performing the refractive adjustments and inducing SA. Based on findings from in vitro and animal studies, two lock-in treatments are performed one or two days apart to assure that the lens is completely stable and not subject to change from environmental UV exposure.

Discussing the UCVA results in more detail, Dr Artal reported that for eyes set for distance, mean monocular UCVA was 1.2 (better than 20/20). However, not surprisingly for this monofocal lens, UCVA was worse for closer distances, decreasing to about 0.40 at 30cm. For the 14 aspheric-treated eyes, mean UCVA was still 0.9 for distance, was nearly 1.0 at 60cm, and remained better than 0.5 (20/40) at 30cm.

The power of being able to customise the amount of induced SA was demonstrated by comparing results with the patients divided into subgroups based on SA in the aspheric eye. Eyes with minimal SA (<-0.1 microns) maintained excellent UCVA for far (mean 0.96) and at 60cm (mean 1.0) and had reasonably good vision at 30cm (mean 0.50) and 40cm (mean 0.75). In the subgroup of patients with more induced SA, there was some compromise in distance vision for the aspheric-treated eye, which was reduced to about 0.8. However, mean UCVA was about 0.95 at both 60 and 40cm and 0.8 at 30cm. In binocular testing, mean UCVA was 1.0 or better at 10m, 60cm and 40cm, and about 0.8 at 30cm.

Dr Artal observed that compared with other methods of presbyopia correction, advanced aspheric monovision has several advantages. The results are much better than with standard monovision because there is less retinal disparity between eyes. In addition, the technique avoids the photic phenomenon associated with multifocal diffractive optics.

“All of our patients were very happy with their outcomes. However, dissatisfaction can occur if the refractive or SA target is not properly achieved. Therefore, obtaining accurate measurements before and during the light adjustment procedure is critical to ensure satisfactory outcomes.â€

Dr Artal told EuroTimes that refinement of the algorithms for the light treatments for advanced aspheric monovision is nearly done.

“Combining the procedure with pre-treatment evaluation using the Adaptive optics visual analyzer developed by Voptica SL to fully customise the induced SA would be an amazing next step,†he concluded.