"Characterization of Visual Problems in Patients With Parkinson's Disease and Application of an Oculomotor and/or Perceptual Therapy Program"

Parkinson's disease (PD) is the second most common neurodegenerative condition worldwide. It is a movement disorder characterised by tremor, rigidity, bradykinesia and postural instability. However, 78% of PD patients report visual problems such as dry eye, reduced visual acuity, visual field defects, impaired contrast sensitivity (CS), impaired eye movements, diplopia, convergence insufficiency, impaired colour vision, visual hallucinations and problems in visual-spatial orientation. In fact, visual dysfunction is one of the initial symptoms of PD. A recent study has found that dopaminergic neurons affected in PD show physiological dysfunctions, but do not die. Currently, there is no cure for PD; treatments consist of controlling symptoms, and the earlier the disease is detected and administered, the more effective they are.

It is hypothesised that a programme of visual oculomotor therapy and/or visual perceptual learning (VPL) could slow or halt the deterioration of oculomotor ability and/or CS in these patients. Visual perceptual learning or VPL is a long-term improvement in performance on a visual task, any relatively permanent change in perception that arises from visual experience. Contrast Sensitivity or CS is the ability of the visual system to differentiate an object from the background in which it is located by the difference in contrast. It is the ability to detect differences in luminance between adjacent areas in an image.

If the results confirm the hypothesis, this study will have a great impact on the PD population because it could slow down the deterioration of oculomotor ability that 75% of them suffer from. It could also slow down the decline in CS that they suffer, as demonstrated by several studies. Consequently, patients would also experience an improvement in their quality of life, as they would be able to continue to perform activities of daily living that are affected by visual impairment such as walking, reading, driving and cooking. This would have a major impact on society as PD affects many people worldwide. In Europe, the prevalence and incidence rates of PD are estimated to be approximately 108-257/100 000 and 11-19/100 000 per year, respectively. Furthermore, this project would expand scientific knowledge because to date there is no literature that has evaluated VPL in patients with PD. However, there is research on amblyopia, Stargardt's disease and other neural pathologies, such as Huntington's disease. Likewise, with regard to oculomotor therapy, there is still a lot of research to be done, as there are few studies on this subject.

This is an analytical, longitudinal, prospective and observational study. In the first phase, to characterise the vision of the population with Parkinson's disease, non-invasive tests would be performed, such as measuring visual acuity, refraction, contrast sensitivity, colour vision, depth vision, the state of binocular vision and visual pathways and eye movements. Simultaneously, a control population will be measured to compare the data obtained in PD patients.

In a second phase, visual oculomotor and/or perceptual exercises would be performed in a group of PD patients to assess whether there is stabilisation of the impairment and/or improvement of these visual skills.