Pattern-reversal VEP tests detect neurological changes sooner
Pattern-reversal visual evoked potential tests detected neurological changes prior to any overt diabetic retinopathy clinical changes, according to a study published in Neurology Research International.
“In the last few years, diabetic retinopathy (DR) is recognized as a neurovascular impairment or sensory neuropathy subsequent to the neurovascular impairment,” Raghda S. Al-Najjar, MS, department of physiology at the Al-Zahraa College of Medicine, and colleagues wrote. “The pattern-reversal visual evoked potentials (PRVEPs) test is the standard and ideal modality for most clinical uses as it is less variable in timing and wave form than other VEP modalities.”
In a prospective study, researchers divided 150 participants into three groups: group A comprised 50 participants with type 2 diabetes without clinically detected DR, group B included 50 participants with type 2 diabetes and clinically detected nonproliferative DR, and a control group included 50 participants without type 2 diabetes or DR. Following division, participants underwent large check PRVEPs testing (60 minutes) and small check PRVEPs testing (15 minutes) to detect any neurological changes.
Study results showed a statistically significant P100 latency delay and P100 amplitude reduction in both groups A and B compared with controls, with differences between group A and group B also statistically significant. Additional test results showed the proportion of abnormal P100 latency were higher than those of P100 amplitude, with higher abnormal proportions seen in the small check PRVEPs testing. Researchers further suggest differences between groups are unrelated to age.
“The results of PRVEPs tests in this study are highly conrmative to the presence of neural alteration in the retina and/or optic nerve, before any clinically diagnosed DR changes, mainly as a conductive defect,” Al-Najjar concluded. “PRVEP tests could be considered as a valid tool to detect any early neurological changes, which could be of great value in the prevention of permanent neuronal loss and blindness. ... Further studies are required with the simultaneous use of pattern electroretinography and PRVEP tests to distinguish between the purely optic nerve changes from those of the retinal abnormality origin.”
Perspective
Back to Top
The effect of blood glucose on the VEP has been known for a long time. In 1997, Anthony J. Adams, OD, PhD, FAAO, from Berkeley Optometry, and colleagues showed that changes in chromatic VEP occur within hours of alteration of blood glucose level. Their work also showed that the blue cone pathway is selectively altered first after glucose rises. This accounts for why color vision is sometimes altered in patients with diabetes even without retinopathy.
Najjar and colleagues argued that the changes in VEP are the result of structural neural damage. This is a part of the larger “chicken and the egg” retinopathy argument that has been ongoing for decades. In diabetic retinopathy, do vascular changes occur first or neural changes? The answer is that you likely can’t separate one from the other. Given how rapidly retinal function changes can occur in response to glucose level, it is likely that an early phase “neuropathy” in the retina occurs first, followed by chronic changes that manifest as structural damage seen on OCT even in the absence of visible retinopathy.
On another note, maybe the most interesting part of this study was extremely low mean HbA1c (approximately 4.07) reported in the control population. An HbA1c below 5 is considered low. Lower isn’t always necessarily better. The Atherosclerosis Risk in Communities Study showed that low HbA1c is associated with increased cancer mortality and all-cause mortality.
References:
- Aggarwal V, et al. Diabetes Care. 2012;doi:10.2337/dc11-2531.
- Schneck ME, et al. Invest Ophthalmol Vis Sci. 1997;38(5):800-10.
Collapse
Read more about