American Academy of Ophthalmology Web Site: www.aao.org
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June 2007

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

New Pharmacologic Approaches to IFIS

Intraoperative floppy iris syndrome (IFIS) might not have met its match yet—but inventive ophthalmic surgeons are doing their best to change that. Recent reports1–7 have shown some success with pharmacologic approaches to the syndrome. The drugs being used, usually intracamerally, include: epinephrine, phenylephrine, atropine, and atropine plus epinephrine.

“It’s something we’ve been using for a couple of years with good success,” said Avinash Gurbaxani, MD, a fellow at Moorfields Eye Hospital in London. In the March Eye, he coauthored a paper about intracameral use of very dilute phenyl-ephrine hydrochloride in IFIS patients.2 He and his colleague used 0.25 cc of phenylephrine hydrochloride 2.5 percent, with 1.0 cc balanced salt solution. These were mixed into a 2-cc syringe.

“We find it useful because IFIS consists not only of the poorly dilating pupil but also a floppy iris,” Dr. Gurbaxani said. “With phenylephrine, not only does it dilate the pupil, but it increases the tone of the iris. It keeps the iris taut and gives you a nice surgical plane. Other methods like using iris hooks are quite cumbersome, they take longer and stretching the pupil is traumatic to the iris.”

A month after Dr. Gurbaxani’s paper appeared, the Journal of Cataract & Refractive Surgery4 published a report on a two-drug strategy, authored by Samuel A. Masket, MD, and Shaleen L. Belani, MD, in private practice together in Century City, Calif. Dr. Masket is also clinical professor of ophthalmology at the University of California, Los Angeles.

They prescribed topical atropine 1 percent three times a day for two days before surgery and gave an additional drop shortly before surgery. Then, after making the paracentesis, they administered 0.3 to 0.5 cc intracameral epinephrine (1 cc of 1:1000 unpreserved epinephrine diluted with 3 cc of BSS) under the iris. They note that patients must be cautioned to continue taking their tamsulosin because of the risk that the atropine otherwise would cause an attack of acute urinary retention.

“Our experience suggests that the symbiosis of intraoperative epinephrine and presurgical atropine represents the best pharmacologic approach because IFIS results from blockage of alpha1A receptors in the iris dilator muscle, leading to possible iris smooth muscle atrophy,” they write.

“By blocking the muscarinic cholinergic receptors in the iris sphincter muscle more completely than all other pupiloplegics, atropine sulfate can help balance the weakened action of the iris dilator muscle. In turn the effect of concentrated epinephrine hydrochloride, a direct-acting sympatho-mimetic, can stimulate the weakened iris dilator.”

David F. Chang, MD, who in 2005 coauthored the first paper identifying intraoperative floppy iris syndrome, said that the Gurbaxani and Masket papers are “important, because they report preliminary results from using two different pharmacologic strategies in tamsulosin patients.”

However, the spectrum of IFIS severity is very large, and success in these surgeries is subjective, Dr. Chang said. “In a large prospective, multicenter study of 169 consecutive cataract surgeries in patients taking tamsulosin, 10 percent of eyes were deemed to have no IFIS, while 43 percent had severe IFIS. For this reason, the ‘success rate’ of any proposed strategy should be prospectively determined in a large study population,” he added.

What does Dr. Chang use in his practice? An intracameral alpha agonist is the most important pharmacologic agent, he said, adding:

  • “Because epinephrine is readily available in the United States, I have used this rather than phenylephrine as an intracameral alpha agonist.”
  • “I do think that adding atropine helps to produce a greater preoperative mydriasis, but the extra benefit is difficult to quantify without a prospective randomized trial.”
  • “I routinely use intracameral epinephrine (1:1000 mixed 1:4 with BSS) in eyes that dilate 4 mm or more preoperatively.”
  • “If the pupil is still not wide enough, viscomydriasis should be considered.”
  • “However, a pupil that is smaller usually indicates severe IFIS and I will place iris retractors in these cases.”
  • If there are added risk factors or complicating circumstances (e.g., pseudoexfoliation, 4+ brunescent nuclei, crowded anterior chamber, or one-eyed patients), “iris retractors have the advantage of being 100 percent reliable at providing and maintaining superb surgical exposure and visibility.”

Dr. Chang cautioned surgeons against overconfidence, saying: “The caveat with pharmacologic strategies is that one must still be prepared for severe IFIS, where the pupil constricts intraoperatively.”
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1 Chang, D. F. Managing intraoperative floppy iris syndrome. Current Insight 2007, Quarter 2 at www.aao.org, then click “Clinical Education.”
2 Gurbaxani, A. and R. Packard. Eye 2007;21(3):331–332.
3 Manvikar, S. and D. Allen. J Cataract Refract Surg 2006;32(10):1611–1614.
4 Masket, S. and S. Belani. J Cataract Refract Surg 2007;33(4):580–582.
5 Osher, R. H. J Cataract Refract Surg 2007;33(3):364.
6 Pringle, E. and R. Packard. J Cataract Refract Surg 2005;31(12):2240–2241.
7 Shugar, J. K. J Cataract Refract Surg 2006;32(7):1074–1075.

Cornea Update 

Dry Eye Treatment May Grow on Trees

A mucinlike polysaccharide from the seeds of tamarind trees someday might give ophthalmologists a dry eye remedy that more closely resembles the glycoprotein that is needed to keep the tear film stable.

Topical applications of tamarind seed polysaccharide (TSP) in low-concentration solutions were at least as effective as hyaluronic acid 0.2 percent at improving dry eye symptoms, and in some areas better, an Italian study has found.1

In two decades of research on the biochemical properties of TSP, this was only the second clinical study looking at the polysaccharide by itself as a dry eye treatment. Investigations of the seed extract largely have looked at TSP as a vehicle for improving the ocular bioavailability of antibiotics and medications such as timolol.

If allowed to crystallize, TSP from an ophthalmic solution takes on the same fernlike shape that crystallized tears do. This branching molecular structure also resembles that of membrane-bound epithelial mucins in the eye. In a healthy tear film, these transmembrane mucins bind chemically to the epithelial surface and make it hydro- philic, facilitating the spread of tears and providing a substrate to which the tear film can adhere physically and biochemically. TSP is thought to fill in when the mucin layer is missing.

In the dry eye study, 30 subjects were randomized to receive one of three medications, three or more times per day: TSP 0.5 percent, TSP 1 percent or hyaluronic acid (Hyalistil, Società Industria Farmaceutica Italiana).

Although the primary objective was to determine TSP’s safety (there were no adverse events), patient questionnaires showed that the TSP 1 percent group had more symptom improvement than the hyaluronic acid group in three areas: trouble blinking, ocular burning and sensation of a foreign body (all P < 0.05). But it was an open-label study, and this might have influenced the patients’ answers, the researchers note.

However, objective tests also showed a difference. Corneal and conjunctival staining, as well as tear film breakup time, also improved over the course of the study in both TSP groups.
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1 Rolando, M. and C. Valente. BMC Ophthalmol 2007;7:5. (Provisional article posted online March 29, 2007.)

Cornea Update 

Bacterial Keratitis Management Made Easy

When someone with bacterial keratitis sits in a general ophthalmologist’s exam chair, the case brings with it unsettled questions for the ophthalmologist over which antibiotic to use, whether to culture and how to predict which infections will rob the eye of a significant amount of visual acuity.

The solution may be a matter of 1-2-3, a classification system long used at a Texas eye practice and which the doctors there shared for the first time this year in Cornea.1

Their formula consists of three numbered, easily applied criteria that identify the corneal ulcers that are highly inflammatory, large and central, making them potentially sight threatening (PST). These eyes have any one of these characteristics:

1) Cells ? 1+ in the anterior chamber (10 cells or greater in 1-mm beam).

2) Dense infiltrate ? 2 mm across the ulcer at any point (determined by setting the slit-lamp beam to span the ulcer’s greatest diameter and reading the measurement on the dial).

3) Edge of the infiltrate ? 3 mm from the center of the cornea (using the same method of slit-lamp light measurement).

If the ulcer does not meet any of those criteria, it can be safely categorized as rarely sight threatening (RST), according to the authors.

The corneal specialists at Houston Eye Associates, which with 29 ophthalmologists is the largest ophthalmology clinic in Texas, did a retrospective review of all their bacterial keratitis cases in a three-year period. They eliminated all cases in which the patient had other ocular pathologies or recent surgery that might have affected visual acuity.

In the remaining 41 eyes of 41 patients, the study showed that all of the ulcers classified as RST under the 1-2-3 rule healed without the patient losing significant BCVA (defined as > 0.20 logMAR or 2 Snellen lines).

The ophthalmologists—Mark C. Vital, MD, Marcel J. Belloso, MD, and Jeffrey D. Lanier, MD—said the formula is a simple screening tool to reveal which ulcers are the most serious.

“In the hands of the general ophthalmologist, the 1-2-3 rule can be a simple, quick and effective guide in making decisions regarding conservative treatment, aggressive treatment, or referral,” they write. “From this study, the 1-2-3 rule suggests that 28.6 percent of ulcers classified into the PST group would have some loss of vision, and 100 percent of ulcers classified into the RST would have slight or no visual loss.”

Furthermore, the criteria might help the general ophthalmologist decide which ulcers merit culturing. The authors write, “The 1-2-3 rule can help guide these decisions and move the management of bacterial keratitis closer to a practical and objective standard of care.”
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1 Vital, M. C. et al. Cornea 2007;26(1):16–20.

RESEARCH REPORT
The Evolution of Color Vision

How easy was it for primates to develop trichromatic color vision? As easy as acquiring a single mutation that made a photopigment sensitive to a different part of the spectrum, according to a report in Science.1

Scientists who study the evolution of the senses have long wondered if an additional evolutionary change was required for the brain to “notice” the new information.

This study not only demonstrated the brain’s plasticity, but also has an important general implication for the understanding of how sensory systems evolved, said Gerald H. Jacobs, PhD, research professor in psychology at the University of California, Santa Barbara. When the first primate acquired the mutation for a third photopigment, the immediate evolutionary advantage quickly put this sensory im-provement into the normal genome, he said.
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1 Jacobs, G. H. et al. Science 2007;315:1723–1725.