Abstract
Purpose: :
Dynamic accommodative measurements provide more information about the accommodative response, including time constants and peak velocities, and allows comparison between accommodation and disaccommodation. The Hartinger coincidence refractometer, a static Scheiner principal optometer, has been converted to a 30Hz dynamic measurement instrument. The precision of the dynamic Hartinger measurements are compared with dynamic infrared (IR) photorefraction with Edinger–Westphal stimulated accommodation in anesthetized rhesus monkeys.
Methods: :
The Hartinger was converted into a 30Hz dynamic optometer by replacing the original internal target with elongated Vernier lines, and attaching a video camera to the eye–piece to allow dynamic recording of the mire separation as the eye accommodates. Edinger–Westphal stimulated accommodative responses of two rhesus monkeys to maximal and to half maximal stimulus current amplitudes were recorded using IR Photorefraction and the dynamic Hartinger. A beam splitter was used to allow both instruments to observe the eye simultaneously. However, interference by the two light sources requires sequential rather than simultaneous recording of accommodative responses. Image analysis was used to track the movements of the mires and calculate their separation. Positions of the mires were determined using Gaussian functions fit to mire luminance profiles. The horizontal separation between the top and bottom mire was converted to accommodation using a predetermined calibration function from a model eye. Standard deviations of the dynamic refraction measures at baseline and at maximum accommodation were compared to determine their relative variability.
Results: :
The Hartinger can be used as a dynamic Scheiner principal recording optometer. The mean standard deviations of the Hartinger measurements were 0.027D, 0.068D, and 0.079D for the baseline, half maximal, and maximal accommodative states, respectively. Photorefraction mean standard deviations were 0.125D, 0.181D, and 0.200D, respectively. The dynamic Hartinger showed an overall better performance as assessed from the standard deviations of measurements.
Conclusions: :
The Hartinger has been converted into a dynamic recording optometer. The Hartinger provides greater precision than IR photorefraction from the same experiments in the same monkeys. Further developments include integrating a high speed (72–400Hz), digital FireWire camera with real–time processing. With this approach, the Hartinger offers a more precise, high speed dynamic recording optometer than IR photorefraction for the measurement of dynamic accommodative responses.
Keywords: image processing • anterior segment • ciliary muscle