Bilateral implantation of multifocal IOLs improves binocular vision at all distances

Further study of adaptation in the context of presbyopic correction and the extent of its effectiveness over time is needed.

Issue: February 2014

Binocular visual acuity substantially improved at distance, intermediate and near vergences approximately 2 years after bilateral implantation of multifocal IOLs, according to a study.

The effects of neural adaptation may be more pronounced under binocular viewing conditions compared to vision with one eye, the study authors said.

“We should not neglect that visual performance is always improved with two eyes, an effect known as binocular summation, when conditions of binocular fusion and overlap are achieved,” Sotiris Plainis, MSc, PhD, and lead author Konstantinos Tsaousis, MD, said in an email interview with Ocular Surgery News. “It is not uncommon to encounter cases of unhappy patients with satisfactory monocular visual acuity.”

Neural adaptation may be a valuable aspect in the success of the simultaneous-image IOL designs to aid in presbyopia correction, Plainis and Tsaousis said.

Study method

In an observational case study, 20 patients underwent bilateral implantation with the diffractive multifocal AcrySof IQ ReSTOR IOL (SN60D3, Alcon Laboratories).

Uncorrected visual acuity was evaluated monocularly and binocularly an average of 26 months after implantation in the second eye, using three versions of the high-contrast, European-wide modified ETDRS logMAR charts at distances of 4 m, 66 cm and 33 cm. Average patient age was 70 years.

The study was published in the Journal of Refractive Surgery.

Outcomes and observations

“In all conditions, logMAR acuity with two eyes was always better or equal compared to the monocular acuity with the better eye,” the authors said in the study.

Mean logMAR uncorrected distance visual acuity improved from 0.07 and 0.21 in the better and worse eye, respectively, to 0.00 logMAR binocularly. Mean logMAR uncorrected intermediate visual acuity improved from 0.18 and 0.32 in the better and worse eye, respectively, to 0.08 logMAR binocularly. Mean logMAR uncorrected near visual acuity improved from 0.20 and 0.32 in the better and worse eye, respectively, to 0.11 binocularly.

“An interesting issue is the role of binocular integration on such forms of plasticity, and recently, another study has shown that binocular vision ameliorates the effect of blur,” Plainis and Tsaousis said. “The findings of the current study are in agreement with this, showing a substantial benefit in binocular summation in patients implanted with multifocal IOLs in both eyes.”

Binocular summation was statistically significant at all distances tested: 0.07 logMAR at 4 m, 0.10 logMAR at 66 cm and 0.09 logMAR at 33 cm, although binocular summation was less evident for high-contrast acuity and decreased with age, according to the study.

Limitations

“Unfortunately, in our study we did not collect preoperative data on binocular summation,” Plainis and Tsaousis said. “There have been recently many studies investigating adaptation effects. Surprisingly, these effects have not been studied with two eyes; thus, it is not established whether there were any binocular interactions in blur perception and adaptation to blur, or whether these interactions change with age.”

Plainis and Tsaousis suggested the need to study adaptation in the context of presbyopic correction and the extent of its effectiveness and time period. They further recommended expanding the preoperative examination to emphasize psychophysical and behavioral investigation in determining whether multifocal IOLs would work best for the patient.

Looking to the future, Plainis said he has been working with his long-term collaborators at the University of Manchester, Ian J. Murray, PhD, and Neil Parry, PhD, SRCS, to advance a technology based on a portable display device to identify presbyopes who are suitable for simultaneous vision or monovision correction. – by Christi Fox

Reference:

Tsaousis KT, et al. J Refract Surg. 2013;doi:10.3928/1081597X-20130318-03.

For more information:

Sotiris Plainis, MSc, PhD, can be reached at the Institute of Vision and Optics, School of Health Sciences, University of Crete, 71003 Heraklion, Crete, Greece; email: plainis@med.uoc.gr.
Konstantinos Tsaousis, MD, can be reached at the Department of Ophthalmology, Friedrich-Alexander University, Erlangen-Nuremberg, Germany; email: konstantinos.tsaousis@uk-erlangen.de.
Disclosures: Plainis and Tsaousis have no relevant financial disclosures.