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Ocular Involvement and Role of Dopamine in Parkinson’s disease

by | Nov 1, 2020 | Manuscripts | 4 comments

Pritam Dutta, M.Optom

Lecturer, Ridley college of Optometry, Assam, India

 

Parkinson’s disease (PD) is a progressive and neuro-degenerative disease associated with various motor and non-motor clinical features(1).  As per World Health Organization (WHO) report, around 6.1 million individuals have Parkinson’s globally (2, 3). The characteristic features of PD commonly include tremor, bradykinesia, instability of posture and rigidity (1). They can also exhibit few non-motor symptoms which include depression, sleep disorders, cognitive issues, and sensory impairments (4, 5). Sensory impairment basically includes the visual disorders (see Table 1) which influences the overall motor functions and hamper the quality of life associated with various daily living activities in patients with PD(6).

 

Table 1: Ocular involvement in Parkinson’s disease

OCULAR CONDITIONS CHANGES IN PARKINSON’S DISEASE
Eye movements Abnormal saccades and pursuits (7) Associated hypometria might be present(8)Affected reaction times (7)
Convergence Poor convergence amplitude (9) Reduced positive fusional vergence at near (9)
Colour vision Impaired possibly due to dopamine dysfunction (10)
Stereopsis Impaired and likely due to underlying pathology in the posterior parietal regions of brain which mediates it (11)
Pupils Mostly likely to affect the parasympathetic system which in turn leads to increased latency, decreased constriction amplitude and larger diameters of the pupil (12)
Visuo-perception Impairment seen in more severe stage and can be an indication of developing PD dementia (13) Possibly due to dopamine dysfunction in the retina or involvement of the fronto-striatal system of the brain (14)
Ocular surface Can be associated with apraxia (15) Reduction in the blink rate leading to abnormal tear film, poor vision, and dryness (16)
Visual hallucination

Seen in PD associated with dementia as a complication. Longer duration of PD, poor vision and reduced activity of the primary visual cortex serves as the predictors (17)

 

Role of Dopamine in PD

Dopamine serves as a neurotransmitter and it is also found to be present in the amacrine cells of the retina (18). It also modulated the retinal photoreceptors and organizes the receptive fields of ganglion and bipolar cells (19). Also in the brain there are two dopamine pathways present: (a) Nigrostriatal pathway originating from substantia nigra and terminating in the striatum (b) originating in the ventral tegmentum and projecting to the limbic system, nucleus accumbens and frontal cortex (20).  Conversely, in PD patients these dopamine levels get depleted in the basal ganglia and frontal cortex involving the superior colliculus which in turn hampers the eye movements (8). (See figure 1)  In addition, decrease in the dopamine levels in visceral ganglia, sympathetic ganglia and artery walls have a direct impact in poor pupil reactivity (8, 21). Thus, degeneration of the dopaminergic neurons in the substantia nigra is the key feature of PD leading to deprived motor output because of increased inhibition of basal ganglia.(21)

 

Figure 1: Depletion of Dopaminergic neurons due to nigrostriatal degeneration on the synaptic terminals of striatal neurons in Parkinson’s disease. 60 % of this loss leads to tremor, rigidity, and balance issues.

 

Table 2: Optometric management in Parkinson’s disease

Management Function
Yoked prisms (2 ∆ base down in each eye) Improves the convergence amplitude by enhancing the functional near visual field, improves reading speed, effect of lifting the environment in those with head down postural problem (22)
Oculomotor rehabilitation Improving the vergence ability, enhancing the saccades and pursuits eye movement(22,23)
Perceptual therapy Improving visual memory, sequential memory, eye-hand coordination, visual discrimination (23)
Others Enhancing the lighting condition, non-visual aids, visual scanning, improving contrast and mobility (22)

 

Conclusion

Visual problems may have a debilitating effect on day-to-day tasks such as walking, reading, or driving, causing Parkinson’s patients to limit their social and physical activity resulting in poorer quality of life. Optometric rehabilitation in PD aims at improving the daily living of patients rather than treating the disease. (see Table 2)  However, irrespective of various side effects, levodopa serves as the first line of drug in PD by operating through the blood-brain barrier and transforming into dopamine at striatal nerve endings.  Therefore, ocular assessment in PD plays a significant role in terms of identifying the clinical signs allowing for a closer understanding of the disease prognosis and managing it to the best possible means to enhance the quality of life of the patients.

 

 References

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  6. Armstrong R. A. (2015). Oculo-Visual Dysfunction in Parkinson’s Disease. Journal of Parkinson’s disease, 5(4), 715–726.
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  10. Piro A, Tagarelli A, Nicoletti G, Fletcher R, &Quattrone A (2014) Commentary: Color vision impairment in Parkinson’s disease. J Parkinsons Dis, 4, 317-319.
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  16. Biousse V, Skibell BC, Watts RL, Loupe DN, DrewsBotsch C, & Newman NJ (2004) Ophthalmologic features of Parkinson’s disease. Neurology, 62, 177-180.
  17. Eberling JL, Richardson BC, Reed BR, Wolfe N, & Jagust WJ (1994) Cortical glucose metabolism in Parkinson’s disease without dementia. Neurobiol Aging, 15, 329-335.
  18. Dowling JE, Ehinger B, & Hedden WL (1976) Interplexiform cell: New type of retinal neuron. Invest Ophthal Vis Sci, 15, 916-926.
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  21. Kordower et al. (2013) Kordower JH, Olanow CW, Dodiya HB, Chu Y, Beach TG, Adler CH, Halliday M, Bartus RT. Disease duration of the integrity of the nigrostriatal system in Parkinson’s disease. 2013;136:2419–2431
  22. Shayler, Geoff. (2011). Optometric Management of Alzhiemer’s and Parkinson’s Diseases, Ageing Vision Part 4. Optometry Today. 41-44.
  23. Cheng, Yuan-Yang & Hsieh, Wan-Ling & Kao, Chung-Lan & Chan, Rai-Chi. (2012). Principles of rehabilitation for common chronic neurologic diseases in the elderly. Journal of Clinical Gerontology and Geriatrics. 3. 5–13. 10.1016/j.jcgg.2011.11.003.

  1. Ganjat on at

    Interesting topic. The arrangement of the content overlaps in mobile view.

    • Vision Science Academy on at

      Hi Ganjat, thanks for raising the point. The mobile view issue has now been resolved.

  2. Yesmin on at

    Information at a glance.
    Nicely written by the author

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