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Susan Ly Johnson, William Eric Sponsel, Rick Trevino, Carolyn Majcher, Matthew Aaron Reilly; Inverse Relationship between Hc & Lc VEP Latency in Paired Glaucomatous Eyes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5846.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucomatous eyes show higher tendency for delayed visual evoked potential (VEP) latency than normals. We reaffirmed this among our clinical pop. and have then observed that an unexpectedly high proportion of patients show high contrast(Hc) latency delay in 1 eye & low contrast(Lc) delay in the fellow eye (Fig 1). In order to ascertain whether a potentially bilaterally compensatory tendency is significantly prevalent among our clinical pop., we evaluated all subjects who exhibited only 1 latency defect per eye to determine the proportion showing the same deficiency (Hc or Lc) in both eyes vs. those having 1 eye with normal Hc latency & the other with normal Lc latency.
Diopsys® NOVA-LX system was used to measure VEP Hc & Lc latency in 440 adult glaucoma patients/suspects, of whom 32(20F, 12M, mean age=55.6) showed only 1 significant Hc or Lc latency defect in each eye. Exclusion criteria included eyes with any other ocular disease, TBI, unexplained visual loss, demyelinating conditions & neuropathies. The confidence interval m-E≤m≤m+E was computed iteratively to est. the corr. Z value using E=Z/(2√n), where n=# of patients. Hc were plotted against Lc latency values for all 64 eyes to determine whether a significant inverse correlation existed for these values among 32 subjects.
With the 64 paired eyes, 32 had mild, 15 moderate & 17 severe glaucoma using standard perimetric scoring criteria, and for all 64 eyes VEP amplitude values were normal. All VEP latency measurements had a reliability ≥70%. There was no preference for VEP latency at either contrast level between OS & OD. 24 of the 32 patients had delayed Lc latency in 1 eye & delayed Hc latency in the other, while only 8 had delayed latencies for the same contrast category in both eyes. This corresponds to about 99.5% confidence(p=0.005) that this difference is not due to chance predicted by the H0(r=0.5). A strong inverse correlation (P=0.0000003) was observed between the Hc & Lc latency values among the 64 paired eyes(Fig 2).
These findings extend our earlier observations on CNS control of binocular neural function in bilateral glaucoma based on visual field refined data analysis(TVST 2014-15). It appears when both magno & parvocellular function cannot be fully supported by either eye, 1 eye will tend to favor 1 function while the fellow eye favor the other. Such complementarity could not exist in functionally independent eyes.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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