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Repeated IOP measurements, iris configuration predict postoperative IOP
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A high preoperative iris cross-sectional area and high convex hull of the iris were associated with reduced IOP after cataract surgery, according to a study.
In addition, multiple preoperative IOP values predicted postoperative IOP more reliably than a single preoperative IOP measurement, Christopher T. Leffler, MD, MPH, the corresponding author, said.
“One thing we showed was that if you average up to four preoperative visits, you do a better job of predicting the postoperative IOP than if you just use a single visit,” Dr. Leffler told Ocular Surgery News. “That’s a very easy thing people can do.”
Results may help surgeons determine which patients are likely to experience the greatest IOP reduction after cataract surgery, the study authors said.
The study was published in the Journal of Cataract and Refractive Surgery.
The prospective study included 77 eyes of 77 patients with open filtration angles who underwent phacoemulsification and in-the-bag placement of a foldable hydrophobic AcrySof SA60AT IOL (Alcon).
Mean patient age was 69.9 years.
Snellen corrected visual acuity, refraction, slit lamp and dilated funduscopic images, biometry and applanation tonometry were evaluated preoperatively and postoperatively. Gonioscopy was used to grade filtration angle width.
The Visante anterior segment optical coherence tomography system (Carl Zeiss Meditec) was used before and after surgery to analyze nasal and temporal iris cross-sectional segments, nasal and temporal angles, and iris thickness.
Follow-up examinations were performed at 1 day, 1 to 2 weeks and 6 to 8 weeks after surgery.
Predictive models, results
Data showed that mean iris convex hull of the iris segments decreased from 5.05 mm2 to 4.19 mm2. The decrease was statistically significant (P < .001).
Mean iris cross-sectional area diminished significantly, from 3.84 mm2 to 3.70 mm2 (P = .01).
“The interesting thing in our study is that the central iris may be just as important in predicting the pressure as the peripheral iris,” Dr. Leffler said.
A coefficient of determination that included three variables predicted postoperative IOP more reliably than a coefficient with only one variable, he said.
“When you look at it as part of a model, which included the anatomic configuration, namely convex hull, plus the mean preoperative IOP, plus whether [patients] have glaucoma, all of those things together had a model r2 of 0.38, meaning that 38% of the variation was explained by the model,” Dr. Leffler said. “That compares with the previous predictor, which was just simply a single IOP measurement, and for that the r2 was 0.13. It was a pretty big improvement over the standard model but there’s a lot of work to be done to really precisely predict the pressure.”
The IOP prediction with three variables was statistically significant (P = .001).
Study results showed that the three-variable model with iris cross-sectional area instead of convex hull predicted IOP with an r2 value of 0.36 and statistical significance (P = .003).
Phacoemulsification settings, incision type and anterior chamber angle or depth did not predict long-term postop IOP. – by Matt Hasson
Reference:
- Pradhan S, Leffler CT, Wilkes M, Mahmood MA. Preoperative iris configuration and intraocular pressure after cataract surgery. J Cataract Refract Surg. 2012;38(1):117-123.
For more information:
- Christopher T. Leffler, MD, MPH, can be reached at Virginia Commonwealth University, Department of Ophthalmology, 401 N. 11th Street, Box 980209, Richmond, VA 23298; 804-828-9315; fax: 804-828-1010; email: cleffler@pol.net.
- Disclosure: Dr. Leffler has no relevant financial disclosures.