Surgeon controversially shuns multifocal IOLs

November 1, 2008

Monovision offers a safe and an effective option while multifocals are a high risk strategy, Dr Graham D. Barrett controversially told delegates during a session that discussed whether surgeons should introduce multifocal IOLs (MFIOLs) into their practice.

Monovision offers a safe and an effective option while multifocals are a high risk strategy, Dr Graham D. Barrett controversially told delegates during a session that discussed whether surgeons should introduce multifocal IOLs (MFIOLs) into their practice.

“Personally I do not currently use multifocals and I would like to explain my reasons and consider the alternatives,” he said.

He said MFIOLs were high risk and compromised sight, while accommodative lenses were unproven. Monovision was his strategy of choice.

Dr Barrett added that describing the technique as monovision is inaccurate and gives patients the wrong impression. “Monovision is really binocular fusion; I use the term omnivision,” he said.

Reviewing MFIOLs, Dr Barrett said that studies confirm reduced contrast sensitivity and associated dysphotopsia, such as haloes. With diffractive MFIOLs, 41% of the light is distributed to near and 41% for distance vision. “18% of the light is simply lost due to high order scattering. Perhaps even more concerning is the fact that the focused image is bathed in the light of the non-focused eye.”

With multifocals, secondary interventions such as LASIK and Yag capsulotomy may be required in up to 30% of patients, and explantation rates as high as 7% have been recorded.Monovision, however, directs 100% of the light to a single focus. “The essence of monovision is to target emmetropia in the first, preferably dominant, eye, for unaided distance vision, whilst the second eye is left with residual myopia to assist with near vision.“A strategy I have found to be particularly helpful is to limit the myopic defocus to no more than 1.5 D, which avoids aesthenopia and preserves contrast sensitivity and stereo acuity,” he said.

He noted that various studies had suggested that contrast is lower as defocus approaches -2.0 D, and similarly stereo vision may be compromised at -2.0 D and greater.

“I aim for emmetropia for distance in the first, preferably dominant, eye and if achieved I aim for 1.25 D of myopia in the second eye. I have found this level of myopia is sufficient to provide a high level of spectacle independence both for distance and near,” he said.

In an assessment of unaided near acuity with patients who had surgery with a monofocal lens, Dr Barrett found that patients with a refractive outcome of 1.0 D were able to read n5 or n8. “The reason this strategy is successful is that the depth of focus in the pseudophakic eye is greater than the phakic eye, which has been termed pseudoaccommodation.”

Dr Barrett conducted a prospective study on his monovision patients and found that 92% had achieved J4 and 20/30 unaided binocular near and distance acuity.

“The reason for the high acceptance of monovision is that the images are spatially congruent and therefore binocular fusion can occur,” he said.

Dr Barrett cited two studies - one a questionnaire to monocular patients, the second a questionnaire to MFIOL patients - and compared the results. The studies showed that only 30% of the multifocal patients rated their vision as excellent, against 66% of monofocals. “Of more concern was the 19% of multifocal patients, who rated their vision as poor, in contrast to only 2% of monovision patients who were unhappy with their vision.”

Dr Barrett described monovision as a ‘winning hand’ with four aces. The first ace was safety, because monovision is reversible and full binocular vision can be achieved at any time with spectacles. The second ace was efficacy, because monovision is not degraded by changes in the macula and against the rule astigmatism, unlike multifocals. It is efficient, the third ace, because preoperative counselling and patient selection are a lot simpler than with multifocals. And monovision patients are extremely satisfied - a winning hand.

 

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