Non-contact optical measurement of lens capsule thickness during simulated accommodation

摘要

Purpose: To non-invasively measure the thickness of the anterior and posterior lens capsule, and to determine if it significantly changes during accommodation. Methods: Anterior and posterior capsule thickness was measured on post-mortem lenses using a non-contact optical system using a focus-detection technique. The optical system uses a 670nm laser beam delivered to a single-mode fiber coupler. The output of the fiber coupler is focused on the tissue surface using an aspheric lens (NA=0.68) mounted on a translation stage with a motorized actuator. Light reflected from the sample surface is collected by the fiber coupler and sent to a photoreceiver connected to a computer-controlled data acquisition system. Optical intensity peaks are detected when the aspheric lens is focused on the capsule boundaries. The capsule thickness is equal to the distance traveled between two peaks multiplied by the capsule refractive index. Anterior and posterior lens capsule thickness measurements were performed on 18 cynomolgus (age average: 6±1 years, range: 4-7 years) eyes, 1 rhesus (age: 2 years) eye, and 12 human (age average: 65±16, range: 47-92) eyes during simulated accommodation. The mounted sample was placed under the focusing objective of the optical system so that the light was incident on the center pole. Measurements were taken of the anterior lens capsule in the unstretched and the stretched 5mm states. The lens was flipped, and the same procedure was performed for the posterior lens capsule. Results: The precision of the optical system was determined to be ±0.5μm. The resolution is 4μm and the sensitivity is 52dB. The human anterior lens capsule thickness was 6.0±1.2μm unstretched and 4.9±0.9μm stretched (p=0.008). The human posterior lens capsule was 5.7±1.2μm unstretched and 5.7±1.4μm stretched (p=0.974). The monkey anterior lens capsule thickness was 5.9±1.9μm unstretched and 4.8±1.0μm stretched (p=0.002). The monkey posterior lens capsule was 5.9±2.0μm unstretched and 5.1±1.3μm stretched (p=0.128). Conclusions: The results indicate that the primate anterior lens capsule thickness changes during accommodation.