Desarrollo de un sensor binocular en visión abierta para el estudio de la acomodación.

Resumo

Goals: Goals of this thesis are: 1. Development and calibration of a Hartmann-Shack binocular sensor (H-S) using infrared radiation (1050nm) to allow unobtrusive measurements of accommodation in open-vision with a real-time pupil tracker (25 Hz). 2. Validation of the instrument under experimental conditions: Measurement of accommodation, convergence, pupil size and monochromatic aberrations in both eyes. 3. Study of the temporal dynamics of accommodation responses (accommodation, vergence and pupil size) for a far-to-near accommodation task. 4. Study of accommodation and refraction in low luminance. 5. Study of the accommodation response in polychromatic light. Methods: The dual-level design of the sensor employs a large dichroic mirror, transparent to the visible and 45º-tilted from horizontal reflecting IR light to the sensor and preserving a natural vision. A calibration arm has been implemented to characterize the sensor. The system has shown to provide accurate accommodation measurements for rotation of eyes until 12.5 °. Linear behavior of accommodation, convergence and pupil size in both eyes was observed with good correlation between relative changes of accommodation and convergence, which validates the use of the instrument in open-view field. Results: In binocular vision accommodation, convergence and pupil size responses were faster than in monocular. It was observed that convergence is performed fast and the rotation of eyes is triggered simultaneously and synchronized in binocular. In monocular vision, accommodation and convergence were slower and had greater intersubject variability. In these conditions, the occluded eye provides a first movement in temporal direction which corresponds to a saccadic movement. Then, eye converges relatively slowly and synchronized with the accommodation thanks to the cross-linked couple accommodation-convergence. The temporal dynamics of accommodation reflexes have shown a great similarity between eyes in binocular vision. A myopic shift of the spherical equivalent was observed in binocular and monocular vision at low luminance with high intersubject variability, including cases with large myopic shifts and other with slight hypermetropic shifts. All cases have shown smaller amplitude in binocular vision. It was calculated that the spherical aberration play a minor role on night myopia. It was found that accommodation changes at low luminance are highly correlated to the tonic position of accommodation or dark focus, and also highly correlated between eyes. However, the resting state of convergence or dark convergence is only moderately correlated with dark focus. Refraction has shown a consistent behavior with accommodation changes as a function of stimulus wavelength with some discrepancies at short wavelength. For green and white stimuli, a similar behavior of accommodation was observed for both far and near steady states. A statistically significant increase of accommodation times was observed with increasing refractive step but no clear trend was observed for mean and peak velocity of accommodation. No significant changes of miosis and convergence amplitude were observed with the changes of refraction step. Conclusion: 1. An infrared binocular sensor was developed to measure accommodation responses and aberrations of both eyes. 2. The instrument has demonstrated good capabilities allowing measurements of accommodation responses for rotation of eyes until 12.5º. 3. The temporal dynamics of accommodation responses showed a great similarity between eyes and a faster response in binocular compared to monocular cases. 4. In monocular vision, an initial saccadic movement of the fellow eye was observed. Then, the cross-linked accommodation-convergence produces convergence synchronized with accommodation. 5. A myopic shift of accommodation at low luminance was observed with high intersubject variability. 6. Accommodation changes were highly correlated with the tonic accommodation and also between eyes, which could explain the similarity of the phenomenon of night myopia between eyes. 7. Tonic convergence and tonic accommodation were only moderately correlated, suspecting a dissociation of such processes in the darkness. 8. Refraction measured in the visible spectrum has shown consistent changes with accommodation to counterbalance the effect of longitudinal chromatic aberration. 9. The accommodation times have shown a linear increase with increasing refraction step which suggests a relation with the wavelength of the stimuli. No clear trend was observed for mean and peak velocity of accommodation.