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Pilocarpine not the whole story in pseudoaccommodation, study indicates

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SAN FRANCISCO — Changes in anterior chamber depth induced by pilocarpine do not always reflect the real effects of accommodative IOLs, a study presented suggests.

Tanja M. Rabsilber, MS, noted that change in anterior chamber depth (ACD) after application of pilocarpine is often used to demonstrate the pseudoaccommodative actions of accommodative IOLs. But other factors may be at work, she said, here at the American Society of Cataract and Refractive Surgery meeting.

One patient with an accommodative IOL experienced good distance and near vision after pilocarpine application, even though the iris showed no movement, Ms. Rabsilber said.

"Nevertheless, the patient showed a good uncorrected distance visual acuity of 20/20 and an uncorrected near visual acuity of 20/30," she said.

"This is a problem that you often have when using machines like the (Carl Zeiss Meditec) IOLMaster because the iris is often used as a reference point for ACD instead of the anterior lens surface, especially in drug-induced miosis," she said.

To investigate this phenomenon, Ms. Rabsilber and colleagues evaluated the changes in ACD in seven patients implanted with the 1CU accommodative IOL from HumanOptics using several measurement technologies. ACD measurements were taken before and after pilocarpine application using the Orbscan 2 system (Bausch & Lomb), the IOL Master and ultrasound biomicroscopy. The patients had a mean age of 55 years.

She said the three methods showed no significant differences in measuring initial ACD values, which ranged from 3.2 mm to 3.35 mm. However, after pilocarpine application, the researchers noted a significant difference in ACD measurements among the systems. Ultrasound biomicroscopy calculated a mean ACD value of 3.15 mm, compared to an average of 2.6 mm with the other two systems.

Ultrasound biomicroscopy calculated a mean 0.3-mm difference in ACD before and after pilocarpine application. The IOLMaster calculated a difference of 0.8 mm before and after pilocarpine, and the Orbscan 2 calculated a difference of 1 mm.

"The mean ACD difference before and after pilocarpine application was lowest [using] ultrasound biomicroscopy," Ms. Rabsilber said.

One drawback to using ultrasound biomicroscopy is that the patient is required to lie down, which may influence IOL positioning, Ms. Rabsilber said.