In search of objective accommodation evaluation

By Ana Hidalgo-Simón MD, PhD

NICE - As clinical trials of accommodative IOLs advance, the question of how best to achieve quantitative measurement of accommodation continues to challenge researchers, Gerd Auffarth MD told a clinical research symposium at the XX ESCRS Congress.

"Although we have relatively accurate measurements of accommodation in phakic eyes, it is quite difficult to objectively measure accommodation or pseudoaccommodation in IOL implants at the clinic.
"Several methods are available but none can provide objective measurements of accommodation following IOL implantation," Dr Auffarth said.

He illustrated his point in a review of his own experience with the HumanOptics Accommodative® 1CU IOL which his team has been implanting for more than a year.
The first studies were performed in the laboratory. The investigators located the H-1CU lens in the capsular bag of isolated human cadaver eyes at the Centre for Research on Ocular Therapeutics and Biodevices, Medical University of South Carolina, Charleston, US. The cornea and the iris were removed in what is known as the open-sky technique.

"We mimicked the stretching and movements of the capsule by applying a circular movement around the ciliary body to see if the lenses were moving and if any change of focus occurred. From the laboratory studies we concluded that the anterio-posterior movement of the IOL optic had accommodative properties," he explained.

Dr Auffarth then decided to measure accommodation in the eyes of live patients implanted with the same type of lens. The clinical study included 25 eyes from 25 patients of whom at least six had a 12 month follow-up period.

Patients ranged in age from 30 to 83 years, with an average of 53. The mean IOL power implanted was 22 D. Average spherical refraction (SE) was +0.5 D and cylindrical refraction was -0.4 D. The mean corrected preoperative visual acuity was +/- 0.3 D.

Subjective clinical results were good. Patients showed good average uncorrected distance visual acuity of 0.7 D to 0.8 D and good functional uncorrected near visual acuity of around 0.5 D, Dr Auffarth said.

The researchers utilised several different methods to evaluate the patients objectively.
These included anterior chamber depth measurements before and after pilocarpine, ultrasound biomicroscopy and corneal topography. The researchers also performed image analysis to assess capsulorhexis overlapping and decentration in all eyes.

Anterior chamber depth measurements taken before and after application of pilocarpine showed some differences depending on the evaluation instrument used.
Dr Auffarth compared results obtained with the Orbscan II (a slip lamp-based system), the IOLMaster and the ultrasound biomicroscopy.

"Before pilocarpine stimulation, most patients had more or less the same anterior chamber depth measurements with the three devices (4.0 mm to 5.0 mm). After pilocarpine, we found marked differences between the different measuring devices," he said.

According to Dr Auffarth, the reason for these discrepancies is that the Orbscan and the IOLMaster do not really measure the distance between the anterior surface of the lens and the cornea. They only go to up to the pupillary rim, especially in myopic eyes.
However, ultrasound biomicroscopy images the anterior surface of the lens and can measure the distance of the chamber up to the epithelium, he explained.

Despite the good results obtained with the ultrasound, he advised delegates to remember that the measurements were taken with the patient lying down. It would be difficult to compare these results with measurements taken with patients sitting or standing. Dr Auffarth concluded that pilocarpine-induced chamber depth changes do not provide an objective method for measuring accommodation. After remarking that automated measurements do not mean accurate measurements, he reminded practitioners to check that the stimulus applied affects to the eye being measured and not the fellow eye.

"There is still an urgent need for effective devices to measure objective pseudophakic accommodation. Existing principles and machines already in use for the phakic eye may hold the key but they would need to be modified," Dr Auffarth said.

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