February 2008

 

CATARACT/ IOL

 

IOL haptics linked to glare


by Rich Daly EyeWorld Contributing Editor

   

Large mesopic pupils and decentered IOLs are likely to increase the appearance of glare images

The haptic insertions of three-piece intraocular lenses (IOL) may be the cause of extraneous glare among some recipients, according to a recent case study.

Research into the source of unwanted glare images from three-piece IOLs after cataract surgery concluded that, under certain conditions, the haptics could interfere with light entering the pupil and producing extraneous images. The case study, titled “Identification of the source of permanent glare from a three-piece IOL,” was published in Eye.

The research stemmed from the case of a cataract patient who received a three-piece, foldable silicone IOL and complained of strong glare images at night beginning three days post-op and lasting at least three years. The surgeons examined the IOL and posterior capsule under mydriatic and nonmydriatic conditions using direct focal illumination from a slit lamp biomicroscope. The novel approach of the study authors to determine the source of the glare included direct focal illumination with both a narrow beam (0.1 mm in width) and small spot (0.1 mm in diameter) to identify the points at which the glare images were stimulated. The authors observed the location of the beam with the slit lamp, while the patient indicated when the glare images were stimulated.

The case study authors concluded that the nasal haptic insertion into the optic was the source of temporal line images arising from lights such as headlamps from oncoming cars and street lamps. The adjacent edge of the IOL also was identified as the likely source of additional cob web-like light rays.

Their conclusion is novel, according to Mark F. Ellis, FRANZCO, FRACS, FRACOphth, senior consultant, Royal Victorian Eye and Ear Hospital, Melbourne, Australia, because such “positive dysmorphosias” were thought to be a problem from the 1990s when sharp-edged acrylic multi-piece IOLs were used. Since then, the design of IOLs has been changed by rounding and glazing the edges to prevent the light scatter caused by internal reflection. The study authors did not identify the type of lens they used other than to say that its edges were “flat with rounded corners.”

Dr. Ellis said his patients occasionally mention positive dysmorphopsias in the two types of IOLs he uses; however, they are usually resolved by three months after surgery, and he has never had to remove any IOL for intractable glare.

His patients still report negative or dark image dysmorphopsias. “These seem to go as the corneal temporal wound becomes less swollen,” Dr. Ellis said. “Some people feel that it is still due to IOL edge.”

In the case study, the authors also concluded that large mesopic pupils and decentered IOLs are also likely to increase the likelihood of unwanted glare images because the patient had 5-mm pupils under mesopic conditions.

“Even if the implant had been centred precisely, the end of the haptic insertion would, at times, encroach into his pupillary area,” the authors noted. “A small error in centration of as little as 0.5 mm effectively places not only the insertion, but also the edge of the optic in the pupillary area. The outcome for this patient is the presence of disturbing and unwanted extraneous images reducing the quality of vision.”

The findings led the case study authors to some controversial suggestions, including the guideline that surgeons consider a three-piece IOL with an optic diameter of at least 6.5 mm or a single-piece IOL for patients with mesopic pupil diameters larger than 4 mm.

Dr. Ellis said pupil size is not very important if the IOL is well centered, with 360-degree coverage by the anterior capsule. The resultant scarring acts as a false pupil, he said.

Jack T. Holladay, M.D., clinical professor of ophthalmology at Baylor College of Medicine, Houston, also disagreed with the need to consider IOLs of 6.5 mm or greater for patients with large mesopic pupil diameters. He agreed that IOL haptic insertions may, under certain conditions, interfere with light entering the pupil.

Dr. Holladay questioned another suggestion that surgeons measure mesopic pupil diameter before surgery to assess the likelihood of extraneous images if 5 mm or 6 mm three-piece IOLs are used.

“There are many variables, and 6 mm optics have stood the test of time, while 5.5 mm IOLs were too small,” Dr. Holladay said.

Dr. Holladay said one way for surgeons to avoid glare images is by not polishing the epithelial cells off of the remaining anterior capsule. A clear anterior capsule could exaggerate the problem, he said.

Editors’ note: Drs. Ellis and Holladay have no financial interests related to their comments.

Contact information
Ellis: mellis@connexus.net.au
Holladay: holladay@docholladay.com

IOL haptics linked to glare IOL haptics linked to glare
Ophthalmology News - EyeWorld Magazine
283 110
283 110
,
2016-07-26T13:36:19Z
True, 2