Parkinson’s disease (PD) is commonly viewed as a disease characterized by motor deficits such as bradykinesia, tremor, and rigidity. Often overlooked on evaluation are PD-associated visual symptoms and signs that can negatively impact daily function and quality of life.

Among the most common visual and ocular symptoms associated with PD are dry eye and ocular surface irritation, a problem that may be prevalent in as many as 60% of patients.¹ This is thought to not only be related to poor production and abnormal composition of tears, but also due to decreased blink rate with resultant subnormal tear distribution.² Parkinson’s patients have also been reported to have problems with eye movements, especially convergence insufficiency.² Convergence insufficiency commonly leads to blurriness at near that improves when either eye is covered, or frank horizontal double vision. This is usually experienced when reading, and further aggravated by ocular surface irritation/dry eye, especially since the blink rate decreases even more during tasks such as reading.¹ Therefore, it is not uncommon for a patient to simultaneously experience monocular double vision (due to dry eye) and binocular double vision (convergence insufficiency) while reading or performing other work at near.

It has been well documented that both color discrimination and contrast sensitivity can be affected early in course of PD.^{1, 2} The pathophysiology of these findings has not been definitively worked out, but theories include loss of retinal dopamine¹ or even posterior cortical neurodegeneration that involves the visual pathways.^{3, 4} These changes in color vision and contrast sensitivity tend to be subtle early on in the disease course and may be responsive to levodopa therapy, but ultimately tend to progress. While these and other ocular and visual disorders have been well documented, there is a paucity of studies as to their effect on patient quality of life and disease morbidity. A study by Worringham et al. found that impaired capacity to detect low contrast visual stimuli was an important predictor in assessing whether or not PD patients would fail in an on-road driving assessment. ⁵ These results echo those of Wood et al. where poor contrast sensitivity accounted for 50% of variance in driving performance in an elderly population.⁶

Impaired contrast sensitivity has been strongly associated with falls in an older population.⁷ In another assessment of predictors of fall risks, specifically in the PD population, it was found that those patients who fell more frequently tended to have more impaired contrast sensitivity⁸ and poorer visual acuity than those who fell less.⁹ These correlations did not meet a statistically meaningful level of significance, however, they are suggestive that vision changes may be a contributing factor to falls which makes sense since patients with imbalance tend to rely more heavily on vision. There is also data suggesting that impaired baseline color vision was associated with a 3-fold risk of PD patients progressing to dementia, which is theorized to relate to posterior neurodegeneration.³

There remains a knowledge gap as to what degree these visual disturbances affect Parkinson’s disease morbidity. Greater awareness of these visual problems in the neurology and eye care professional communities would lead to earlier recognition and targeted therapies to improve quality of life. A simple example is dry eye/ocular surface irritation, for which artificial tears are the initial therapy and are generally effective. Identification of convergence insufficiency can lead to the prescription of eye movement training programs (convergence exercises) or prism therapy. Further research efforts in this area may lead to more comprehensive patient care and reduction in disease morbidity.

1. Ekker MS, Janssen S, Seppi K, Poewe W, de Vries NM, Theelen T, Nonnekes J, Bloem BR. Ocular and visual disorders in Parkinson's disease: Common but frequently overlooked. Parkinsonism Relat Disord. 2017 Jul;40:1-10. doi: 10.1016/j.parkreldis.2017.02.014. Epub 2017 Feb 21. Review.
2. Armstrong RA. Visual Dysfunction in Parkinson's Disease. Int Rev Neurobiol. 2017;134:921-946. doi: 10.1016/bs.irn.2017.04.007. Epub 2017 May 31.
3. Anang JB, Gagnon JF, Bertrand JA, Romenets SR, Latreille V, Panisset M, Montplaisir J, Postuma RB. Predictors of dementia in Parkinson disease: a prospective cohort study. Neurology. 2014 Sep 30;83(14):1253-60. doi: 10.1212/WNL.0000000000000842. Epub 2014 Aug 29.
4. Rimona S. Weil, Anette E. Schrag, Jason D. Warren, Sebastian J. Crutch, Andrew J. Lees, Huw R. Morris; Visual dysfunction in Parkinson’s disease, Brain, Volume 139, Issue 11, 1 November 2016, Pages 2827–2843
5. Worringham CJ, Wood JM, Kerr GK, Silburn PA. Predictors of driving assessment outcome in Parkinson's disease. Mov Disord. 2006 Feb;21(2):230-5.
6. Wood JM. Age and visual impairment decrease driving performance as measured on a closed-road circuit. Hum Factors. 2002 Fall;44(3):482-94.
7. Lord SR, Clark RD, Webster IW. Visual acuity and contrast sensitivity in relation to falls in an elderly population. Age Ageing. 1991 May;20(3):175-81
8. Latt MD, Lord SR, Morris JG, Fung VS. Clinical and physiological assessments for elucidating falls risk in Parkinson's disease. Mov Disord. 2009 Jul 15;24(9):1280-9.
9. Wood BH, Bilclough JA, Bowron A, Walker RW. Incidence and prediction of falls in Parkinson's disease: a prospective multidisciplinary study. J Neurol Neurosurg Psychiatry. 2002 Jun;72(6):721-5.