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News in Review
A Look at Today’s Ideas and Trends
By Linda Roach, Contributing Writer
Edited by Brian A. Francis, MD
 
 

Can Light Damage the Retina in RP Patients?

Western States on Lookout for West Nile Virus

What's in a Name?

While You Were Sleeping: Contacts and Keratitis

New Bottle for Sterile Drops


Can Light Damage the Retina in RP Patients?

Light-induced retinal damage in dogs with a naturally occurring form of retinitis pigmentosa caused by a rhodopsin mutation has raised the question of whether clinically common levels of ophthalmic lighting, such as in fundus photography, might accelerate neuronal death in the eyes of RP patients.

The study involved a group of dogs with a naturally occurring mutation in the rhodopsin gene, RHO. As they investigated the effect of light on the dogs’ disease course, they were surprised to find that shooting a photo montage caused cell death in overlapping circular areas, corresponding to the flashes.

Light exposure during ophthalmic exams should be reduced for reitinitis pigmentosa patients.
Caption: One study suggests that light exposure
during ophthalmic exams and procedures should be
reduced in retinitis pigmentosa patients in order to
minimize disease progression.


Further study showed that focal light equivalent to a photo flash caused visible lesions by two hours. Four weeks later, outer retinal tissue had decreased—but the areas of damage were smaller than had been observed 24 hours after the light exposure. The latter suggested a repair process, so they then reduced the focal light dose tenfold. The retinas looked normal for up to three weeks, but then steadily degenerated over about six months.

In the paper, which reached publication just four months after submission,¹ the researchers postulate:

  • That brief, bright flashes during fundus photography trigger photoreceptor injury leading to retinal degeneration by one month.
  • That exposure of dog retinas to moderate light, such as occurs during vitreoretinal surgery, results in a more covert form of injury leading to a slow retinal degeneration time-course lasting approximately six months.
  • That this mechanism might explain why environmental light, concentrated by anatomy or other factors onto certain areas of the retina, could lead to the regional retinal degeneration characteristic of some forms of RP caused by rhodopsin gene (RHO) mutations.

With bluntness rarely seen in basic science, the researchers urge clinicians to limit their use of bright lights in the eyes of RP patients known or suspected to have RHO mutations, which—among more than 100 known RP genes—are thought to be one of the most common molecular causes of the disease.

“Immediately, it would be judicious to modify clinical examination of patients with RHO mutations,” the paper concludes. “Retinal photography should not be standard in these patients, retinal examinations should be of short duration by using the least light possible, and light exposure during ocular surgery should be reduced.”

They added that preclinical and clinical trials also should be modified. “Outcome measures, such as photographic montages and prolonged light-adapted cone flicker ERGs (untested in the current experiments), may be ill-advised,” they write.

“It is important for people with dominant RP caused by the rhodopsin mutation to talk with their ophthalmologist about minimizing their light exposure,” said Stephen Rose, PhD, chief research officer for the Foundation Fighting Blindness, which helped fund the study. “Genetic testing to determine the form of RP enables patients to respond immediately to these critical findings. In this case, people with the rhodopsin mutation can take vision-preserving action right away.” He added that for people who don’t know if they have the form of RP addressed in the study (the dominant form of the rhodopsin mutation), the study provides a reason to undergo genetic testing.

On another level, David Sliney, PhD, of the Laser Optical Radiation Program of the U.S. Army Center for Health Promotion and Preventive Medicine, said the surprising results would be an important contribution to the understanding of phototoxicity, if they are confirmed. Dr. Sliney’s research has included studies of light safety in ophthalmology.

Until this paper, light-induced retinal damage was thought to be either temperature dependent or a photochemical response to usually chronic doses of ultraviolet light, he said.

“If it is true, and if it applies to human RP, then it’s a totally new type of light damage that can be dependent on the light being delivered in a very short exposure duration,” Dr. Sliney said. “Normally, photochemical events are only dominant for continuous, lengthy exposure, but apparently there may be one set of RP patients in whom repair of normally transient effects triggers this adverse response.”

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1 Cideciyan A. V. et al. Proc Natl Acad Sci USA 2005;102(14): 5233–5238.

Comprehensive

Western States on Lookout for West Nile Virus

That season is here—the one in which warm temperatures and the rains of late spring release a new crop of hungry mosquitoes. For ophthalmologists in the western United States, this will warrant a new level of vigilance for West Nile virus that their eastern colleagues had to adopt several years ago.

The mosquito-borne disease has moved steadily westward over the last several years, with California’s case count reaching 391 during 2004, according to the U.S. Centers for Disease Control and Prevention. Only the Pacific Northwest, including Idaho and Montana, remains relatively untouched with 14 deaths and 129 cases of neuroinvasive disease.

As recently as 2002, the only ophthalmic manifestation thought to occur was optic neuritis, but a series of case reports since February 2003 have made clear that ophthalmologists might see various problems caused by the virus.¹

These can be quite serious, as Alaska retinal specialist Scott A. Limstrom, MD, found while completing a fellowship in the Midwest in 2002 and 2003. Dr. Limstrom, who practices in Anchorage, said he saw four cases of West Nile chorioretinitis. One of the patients had not been previously diagnosed with the infection when she sought ophthalmic help, and another suffered permanent visual loss, he said. Three out of four were diabetics, consistent with the public-health consensus that people with significant comorbidities  usually are most affected by West Nile.

“She developed occlusive vasculitis, and her vision dropped to 20/200 in one eye, 20/400 in the other eye and she didn’t recover,” Dr. Limstrom said. “There are a number of patients who have the West Nile infection and develop significant retinal problems. Ophthalmologists should be aware that these can develop, and should know that we might actually be the first physicians to make the diagnosis.” 

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1 Garg, S. and L. M. Jampol. Surv Ophthalmol 2005;50(1): 3–13.

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More Info
The CDC has lots of information on West Nile virus on its Web site. Go to www.cdc.gov/ncidod/dvbid/westnile/clinicians/ for information and guidance for clinicians as well as patient education materials.

Sports Zone: What’s in a Name?

The moniker of a 4-year-old filly on the New York horse racing circuit this summer is enough to make an ophthalmologist wonder: Could it be that a refractive surgeon is joining the thoroughbred set with a horse named . . . Lasik?

But the thoroughbred with the ophthalmic name—whose winnings in the last year ($137,000+) would pay for perhaps 90 eyes’ worth of refractive surgery—got her name the old-fashioned way, says co-owner Samantha Siegel, of Santa Monica, Calif.

She and the other owner, her father Mace Siegel, were trying to come up with a Jockey Club–approvable name for the horse they were buying, one that would pass muster but also honor the tradition of reflecting the horse’s breeding. “There are so many rules, like it can’t be longer than 18 spaces, and you can’t use anything that’s been used in the last 15 years,” she recalled

As they stared at the names of the sire and dam—“Mazel Trick” and “Clear Vision”—the answer became obvious. “My dad and I were staring at those two names, looking for ways to be clever. He suggested Lasik, and I said, ‘That’s perfect.’”




Cornea

While You Were Sleeping: Contacts and Keratitis

There’s both comfort and a cautionary tale buried in the statistics of a recent population-based study of severe microbial keratitis in contact lens wearers.

The study of more than 26,000 contact lens wearers seen in one year at the Royal Eye Hospital, Manchester, England, confirmed that extended-wear silicone hydrogel lenses are much less likely to lead to such infections than other soft contact lenses worn continuously. Conventional lenses had five times the infection risk of silicone hydrogels.¹

But the study showed it’s still best not to sleep in contacts. While silicone-hydrogel lenses are noted for their high oxygen permeability, people who slept in them were three times as likely to develop severe keratitis as soft lens wearers who didn’t sleep in their lenses. The rate of serious infection among those who slept in silicone-hydrogel lenses was 19.8 per 10,000.

This British study’s numbers on both keratitis incidence and relative risk in contact lens wearers of all types were higher than has been reported in previous studies. For instance, it found the baseline incidence of severe keratitis with daily wear hydrogels was 1.7 times the rate seen in other large studies conducted as recently as 1999.

The team of hospital and University of Manchester researchers ascribed the differences to their study’s single-site design, higher rate of capture of all contact lens wearers, and more rigorous diagnostic criteria for severe keratitis.

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1 Morgan, P. B. et al. Br J Ophthalmol 2005;89:430–436.

Patient Care

New Bottle for Sterile Drops

Amid talk of wavefront-adjusted lenses and lightning-fast lasers, one of the hits of the spring meeting of the American Society for Cataract and Refractive Surgery was an ingenious solution to a (literally) irritating problem.

The device: a veritable Rube Goldberg contraption that gives patients their first multidose bottle of preservative-free artificial tears. 

Pfizer’s “dispensing system” for its Visine Pure Tears consists of a two-chambered bottle with special valves that keep the liquid sequestered in a sterile chamber until the user “clicks” a single drop into a dispensing chamber for delivery to the eye. One click, one drop, and no rebound of any fluid back into the sterile chamber.

Just in case, though, each drop first encounters the device’s silver bullet—that is, a small coil, made of silver because of its natural antibacterial properties. 

“The bottle itself is the preservative,” said a Pfizer spokesman.

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