LENS TECHNOLOGY

The light adjustable lens (LAL, Calhoun Vision) implant offers a unique technology which allows customised and changeable postoperative refractions with a high degree of predictability and an excellent safety profile, according to speakers at the XXXI Congress of the ESCRS in Amsterdam.

“Although the implant is currently only used in a handful of centres in the UK, the LAL is gaining popularity with cataract and refractive surgeons worldwide as it offers the possibility of non-invasively addressing postoperative errors of refraction and gives us the ability to use the implanted refractive outcome as a guide to how presbyopic correction is suited to the individual’s needs,” said Hasan A Usmani FRCOphth, Blackpool Victoria Hospital, UK. He said that the lens offers the possibility of making non-invasive sphero-cylindrical adjustments postoperatively, thereby negating the risk of refractive surprises that can occur with conventional IOLs.

Dr Usmani’s retrospective study included data for 36 eyes of 22 patients who underwent cataract and refractive lens exchange and opted for monovision as their preferred method of presbyopic correction.

All patients underwent uncomplicated standard phacoemulsification, with UV protection for up to 14 days post implantation of the lens. Where possible the dominant eye was implanted first, aiming for emmetropia. The non-dominant eye was implanted approximately one month later for near with a refractive target of -1.25 D. Refraction was undertaken at each adjustment visit and adjustments continued up to a maximum of three times until customisation of near vision by individual patients was achieved, and the lens power was then locked in with a final treatment.

The mean patient age was 55.2 years and preoperative spectacle spherical equivalent ranged from -16.00 to +6.50. The mean follow up was six months with a range of four to 18 months.

Looking at the results, Dr Usmani noted that most of the cases ended up slightly myopic, giving them excellent near vision.

Overall, 92 per cent of patients were within 0.50 D and 75 per cent within 0.25 D of the desired refractive target. Binocular near vision of N8 or better was achieved in 91 per cent and N6 in 86 per cent of patients, with binocular distance vision of 6/6 or better in 83 per cent of patients. Over 86 per cent of patients achieved both uncorrected binocular 6/9 distance vision and near vision of N6 or better.

Positive assessment

The LAL also received a positive assessment in a separate study presented by Tobias Neuhann MD, Marienplatz Eye Clinic, Munich, Germany. Dr Neuhann’s study included 98 eyes with a mean patient age of 64. Of the 98 eyes with two years' follow-up or more, 64 were classified as virgin eyes and 34 as complicated eyes – 23 were post-LASIK, four eyes had undetected keratoconus that was spotted during the preoperative evaluation, seven eyes had no reliable IOL Master axis measurement.

“Posterior pole cataracts are often very difficult to measure and for these patients I like to use the LAL because I am not sure exactly where to go and which dioptre of lens to implant,” he said.

Some eyes had a slight over-correction and practically no under-corrections after the surgery, said Dr Neuhann. He said that the astigmatic correction was particularly impressive in this series of patients.

“The postoperative cylinder is almost always below 1.0 D after the surgery and more often it is 0.5 D or less. This is something that I cannot achieve with a normal toric lens because the small cylinders between 0.5 D and 2.0 D are very difficult to measure and all our measurement devices are not precise enough. With the LAL, we can adjust the astigmatism corrections after the subjective refraction and it gives very impressive results in the low dioptre toric range,” he said.

The refractive results were stable over the two-year follow-up period, noted Dr Neuhann and the predictability data was also first rate. “Around 64 per cent of patients were within 0.25 D of target refraction, 86 per cent were within 0.5 D and 100 per cent were within 1.0 D – this is something which is hard to achieve with the current formulas,” he said.

In terms of side effects, Dr Neuhann said that most patients experienced transitory erythropsia after UV treatment, with the first lock-in treatment typically producing the strongest erythropsic effect. Two patients recorded a loss in visual acuity from 20/20 to 20/200 in one of their treated eyes after the first lock-in procedure. OCT scans of these eyes showed inflammation of the photoreceptor layers and rehabilitation of visual acuity took up to six months. One patient had fibrin in the anterior chamber, which resolved after tissue plasminogen activator treatment, and two other patients had cystoid macular oedema, one before the treatment and one after lock-in treatment.

Dr Neuhann said that the results showed good reliability, stability and efficacy for the LAL, both in virgin and difficult eyes such as post-LASIK and keratoconic cases.

Tobias Neuhann: dr.neuhann@email.de

Hasan A Usmani: hasan.usmani@gmail.com