Abstract:
Several goals were pursued in the development of this work, including the development of a novel in vivo method to measure the ciliary muscle of a human subject non-invasively during accommodation, the characterization of the recorded muscle signals based on the accommodative abilities of the subject (control, presbyopic, or pseudophakic), and the development of a device that would utilize the recorded muscle signals to mimic the appropriate level of accommodation for the user, actuated through the use of a variable refractive lens. The different elements of the thesis are explored in different sections of this dissertation.
Prior to the development of an assistive device that compensates for missing accommodative ability, trials to record the accommodative signals of the ciliary muscle during accommodation were performed, using a custom contact lens electrode. Three groups, each composed of ten subjects, were examined: control subjects, presbyopic subjects, and pseudophakic subjects. The effects of different pharmacological agents were additionally examined. From these trials, it was discovered that the novel recording method used produced results that were both useable and repeatable.
An analysis of the recorded signals revealed that the parameter most sensitive to changes in accommodative effort was the maximum signal amplitude elicited by focusing on pre-defined targets set at different distances. This parameter differed between groups, with presbyopes showing the lowest signal amplitudes, and control subjects exhibiting the highest amplitudes. Interestingly, the pseudophakic group was able to produce stronger accommodative signals than the presbyopic group. Though cyclopentolate depressed the accommodative amplitudes recorded, phenylephrine did not have an effect.
Using the results from the ciliary muscle studies, an assistive device was developed. Signals recorded from the contact lens electrode were amplified, then, using a linear relationship of distance versus accommodative signal, the device predicted the target refraction. To achieve this refraction, a liquid crystal lens was used, the refractive power of which could be controlled by the processed ciliary muscle signal. In preliminary proof-of-concept trials, the visual acuity of presbyopic subjects at near targets was found to significantly increase when using the device, while the far visual acuity remained unaffected. This proves that the device is able to use the neural signals produced by the ciliary muscle in order to simulate accommodation through the use of a liquid crystal lens, the refractive power of which is controlled by electrical ciliary muscle response.
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