Ultra-thin lens reveals mystery accommodation

By Roibeard O'hÉineacháin

NICE - A new thin-as-a-hair IOL (ThinOptX®) which is implantable through an incision smaller than 2.0 mm provides good visual results and may even impart some pseudoaccommodation, a Spanish ophthalmologist told the XX ESCRS Congress.

"The ThinOptx IOL is a plastic polymer lens which is 40 microns thick with a special optical design such that the lens has the same thickness regardless of the refractive power.
"It can be rolled for insertion into a 1.4 mm to 1.5 mm incision and unfolds completely within 10 seconds of implantation," Jorge Alió MD said.

In six eyes of six cataract patients who underwent micro-incision implantation of a ThinOptX IOL, the mean postoperative spherical equivalent (SE) was -1.48 D and mean BCVA was 20/27 after a follow-up of six months.
Postoperative refractive sphere was -0.4 D and astigmatism did not change according to the preoperative level.

In addition, near visual acuity was 20/25 without correction and 20/27 with best correction for distance. All achieved a BCVA for near of 20/20 or better with mean add of 1.9 D, Dr Alió reported.

"We got the A constant to target at about -0.5 D of final refractive sphere. At this point, the predictability of the refraction was excellent.

"But we did have a surprise finding in the good near visual acuity achieved with BCVA. This lens probably provides some accommodation and this needs to be confirmed because it may be an additional advantage of this technology," he said.

Implantation of the lens did not appear to induce any astigmatism. In fact, the cylinder was slightly lower but without reaching significant values.
In addition, there was no difference in contrast sensitivity in the eyes implanted with the ThinOptX lens and that of their fellow eyes, which were implanted with a conventional acrylic IOL.

The patients included three men and three women with LOCS 3 classification senile cataracts. All had normal axial lengths and normal keratometry. Patients underwent micro-incision cataract surgery with the Dodick Laser PhotolysisTM system.
The mean incision size was 1.6 mm; mean power of the lens 18.83 D; and the A constant was 118.84, he noted.

"Incision size is inversely correlated with surgical control. With micro-incision cataract surgery, we create a much more controllable environment. To make this surgery possible we need to have a separation of irrigation and aspiration and work with both hands at the same time.

"We need lasers to reduce the trauma to intraocular structures. And finally we need new IOL technology so that surgeons performing these procedures will not need to enlarge the wound," Dr Alió said.

The ThinOptX lens is manufactured in such a way that while the anterior surface has a continuous curvature like a conventional lens, the posterior surface is divided into steps which serve to focus all the rays on a single point, thereby eliminating spherical aberration.
The manufacturers assert that the lens is not a diffractive Fresnel lens, but rather should be termed a diffractive lens.

"The optical quality of this lens has been studied and modulation transfer function (MTF) and other optical variables have been analysed.
"This really proves this lens provides adequate optical quality to match the standards of current IOLs, something that corresponds to our preliminary clinical results," Dr Alió explained.

The means by which the lens appears to afford patients accommodation remains somewhat a mystery, Dr Alió noted.
Ultrasound biomicroscopy images of the lens show that it bends slightly forward at least at the early postoperative period up to the third month which might account for the good near visual acuity with best correction for distance.

William Callahan, one of the designers of the lens, suggested an alternative theory which is that the accommodative effect results from the greater depth of field the lens achieves.
Dr Alió noted that in his first few implantations, he rolled the lens prior to implantation with his fingertips.

Since then, ThinOptx manufacturers have developed a new folding and insertion device enabling surgeons to roll the lens instrumentally and which he now uses.
"We now have a lens we can implant through a 1.4 mm incision. The new improvements in rolling technique with the ThinOptX lens will further promote its use in cataract surgery," Dr Alió said.

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