Research by Henri Leinonen (University of Eastern Finland, Finland) has highlighted the potential use of retinal testing as a screening tool for neurodegenerative disease in the future.
Since the retina of the eye is an integral part of the CNS that can be studied non-invasively, Leinonen focused his PhD project on the investigation of retinal functional abnormalities in neurodegenerative disease.
To investigate this, he utilized electrophysiological visual tests such as electroretinography and visual evoked potentials, both of which can be applied to both laboratory animals and humans. Electroretinography involves the tracking of retinal function with corneal or skin electrodes while visual evoked potentials measure visual cortex function.
These techniques were therefore utilized to evaluate visual attributes in three distinct genetically engineered mouse models of human CNS diseases including Huntington’s disease and Alzheimer’s disease.
In the Huntington’s disease mouse model, while retinal structure remained largely normal despite toxic huntingtin protein accumulation, in line with patient data, day and color vision-associated retinal dysfunction was presented.
The Alzheimer’s disease model demonstrated hastened rod-mediated inner retinal responses to dim light flashes compared to wild-type controls. This is believed to be through impaired cholinergic neurotransmission, a causative factor of pathological memory deterioration associated with the disease.
Additionally, retinal degenerative changes mimicking those occurring in age-related macular degeneration were demonstrated in a mouse model of late infantile neuronal ceroid lipofuscinosis. These included impaired function of retinal pigment epithelium and eventual blindness.
Together, the results indicate that neurodegenerative changes may occur in the brain and eye simultaneously. Therefore for a number of CNS diseases, eye examination serves as a potential non-invasive screening tool that could facilitate earlier detection compared to current methods.
Sources:www.alphagalileo.org/ViewItem.aspx?ItemId=168527&CultureCode=en; http://epublications.uef.fi/pub/urn_isbn_978-952-61-2200-7/urn_isbn_978-952-61-2200-7.pdf; Leinonen H, Rossi M, Salo AM et al. Lack of P4H-TM in mice results in age-related retinal and renal alterations. Hum. Mol. Gen. doi:10.1093/hmg/ddw228 (2016) (Epub ahead of print).