Lens-based technologies to study accommodation and refraction
- Autores: Carlos Otero Molins
- Directores de la Tesis: Jaume Pujol Ramo (dir. tes.), Mikel Aldaba Arevalo (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Pablo Artal Soriano (presid.), José Manuel González-Méijome (secret.), Susana Marcos Celestino (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Óptica por la Universidad Politécnica de Catalunya
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- Resumen
A visual stimulus can be presented in free space or through lens-based systems. Interestingly, it has been reported many times in the past that some subjects have poorer accommodative responses when optically stimulated, with no aparent reason. However, this limitation has not precluded the use of lens-based systems in ophthalmic devices, virtual reality displays or research setups, probably because it is outweighed by some advantages such as the computer-control of the focal plane of the stimuli. Under this general context, the objective of this thesis is to apply lens-based technologies (from computer-controlled electró-optical lenses to Badal Systems) to study accommodation and refraction.
The methodology of this thesis is structured in 6 studies. The first three studies investigate the response of the accommodative system when optically-stimulated with a Badal optometer. The remaining 3 studies take advantage of electro-optical varifocal systems to investigate new methodologies related to the automated subjective refraction and the accommodative facility test. Concretely, the fourth study is a clinical validation of a new automated refraction algorithm and is the only study thatworks specifically on eye¿s refraction. The fifth and sixth studies use an electro-optical liquid lens to present a repeated step-like stimulus at different accommodative distances. The fifth study validates a new accommodative facility test that integrates both the far and near accommodative facility testwith random changes of accommodative stimulus and, the sixth study explores how the predictability of a stimulus affects the accommodation dynamics.
The results of the first three studies show that previously reported differences in accommodative response when using lens-based methods compared to free space viewing may be explained by the effect of other factors such as the refractive error or field of view rather than the method to stimulate accommodation. It is also shown that the most accurate accommodative responses are obtained for fields between 8º and 10º which suggests that there may be an optimum peripheral retinal image size for accommodation stimulation. Also, it is shown that the only factor that in isolation significantly affects the accuracy of the accommodative responses is the type of refractive error. And finally, it is also shown that the accuracy of the accommodation response generally improves with a 2-dimensional stimulus with apparent depth cues and simulated out-of-focus blur in a relatively large field of view. Even though these conditions may not be adequate for all individuals, they can be used to improve the overall visual comfort in those virtual reality systems that use a varifocal optical system to change the focal plane of a 2-dimensional surface or visual simulators.
The results of the study 4 show the first implementation of a potential novel method of performing non1cycloplegic subjective refraction in adults without clinician suport. Although this method has some limitations thatwarrant further research and it should be tested in a wider population in terms of age4 refraction and different ocular conditions4 it is precise and more accurate than objective refraction methods and it has the potential to be incorporated in novel lens1based technologies to improve primary eye care services in developing countries.
And finally, the last two studies showed also the first implementation of a new accommodative facility test that integrates both the far and near accommodative facility testwith random changes of accommodative stimulus. This new methodology is a faster test than performing both the near and far accommodative tests and it provides more information than conventional accommodative facility tests. Additionally these two studies showed that the prediction operator does not exist in accommodation and the unpredictability of the stimulus does not affect the accommodation dynamics.
