Laird Harrison

March 05, 2015

CORONADO, California — Changes in the retina might predict disease progress in patients with Parkinson's disease, according to a new study presented here at the North American Neuro-Ophthalmology Society 2015 Annual Meeting.

"The eye is a window to the brain," Manpreet Kaur, MD, from the Prasad Centre of Ophthalmic Sciences at the All India Institute of Medical Sciences in Delhi, told Medscape Medical News.

Dr Kaur and her colleagues compared 20 patients diagnosed with idiopathic Parkinson's disease with 20 healthy control subjects matched for age to look for possible retinal biomarkers.

Previous research has established links between Parkinson's disease and changes in the human retina. Neurons that produce dopamine are present in the human retina and dopamine is affected in Parkinson's.

People with Parkinson's disease often have visual deficits, and previous studies have revealed thinning of the peripapillary retinal nerve fiber layer and decreased electrical activity at the fovea in these patients.

There was no significant difference in macular thickness or volume, and color vision, intraocular pressure, anterior segment, and fundus were all normal in the two groups.

However, on spectral-domain optical coherence tomography, the retinal nerve fiber layer and the ganglion cell inner plexiform layer were thinner in the Parkinson's group than in the control group.

In addition, on multifocal electroretinogram, a decline in retina electrical activity was seen in the Parkinson's group. And contrast sensitivity was significantly lower in the Parkinson's group than in the control group.

Table: Differences Between Groups

Variable Parkinson's Group Control Group P Value
Best corrected visual acuity 1.00 1.00 .481
Contrast sensitivity 1.46 1.56 .001
Mean retinal nerve fiber layer thickness (µm) 106.70 116.70 .18
Mean ganglion cell inner plexiform layer (µm) 71.50 81.50 .001
Root mean square noise voltage on multifocal electroretinogram 1139.30 1477.40 .023

 

In the Parkinson's group, there was a significant correlation between electrical activity and the severity of symptoms, and between electrical activity and the duration of the disease.

There was a correlation between mean retinal nerve fiber layer thickness and Unified Parkinson's Disease Rating III Score, but no other correlations between structural changes and disease severity or duration.

The researchers conclude that contrast sensitivity and multifocal electroretinogram results are sensitive measures of visual functional impairment in patients Parkinson's disease, and can indicate subclinical visual dysfunction in the presence of normal visual acuity.

"A longitudinal study is needed to see if any of these can be used as biomarkers," said Dr Kaur. "It might tell us how the disease will progress."

These findings cannot be used to diagnose Parkinson's disease because many other conditions, such as multiple sclerosis, neuromyelitis optica, and Alzheimer's disease, can produce the same findings, she pointed out.

It is not a surprise that there was no significant difference in the macula between the Parkinson's group and the control group, said Eitan Rath, MD, from the Lin Eye Clinic in Haifa, Israel, who was not involved in the study.

"If it's a neurologic disease, maybe there is a loss of nerve fiber," said Dr Rath.

Dr Kaur and Dr Rath have disclosed no relevant financial relationships.

North American Neuro-Ophthalmology Society (NANOS) 2015 Annual Meeting: Abstract 167. Presented February 24, 2015.

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