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Editors Selection IGR 10-4

Anatomical Structures: The visual pathway degenerates centripetally

Neeru Gupta

Comment by Neeru Gupta on:

92667 Progression of Visual Pathway Degeneration in Primary Open-Angle Glaucoma: A Longitudinal Study, Haykal S; Jansonius NM; Cornelissen FW, Frontiers in human neuroscience, 2021; 15: 630898


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In this paper, Haykal and co-workers report findings from diffusion-weighted MRI scans of the optic tracts and optic radiations in 12 primary open angle glaucoma (POAG) patients from 2017- 2018. The same patients had been recruited to earlier MRI studies in 2008-2009 and 2013- 2014 and these served as the initial MRI scans to which the latter ones in this study were compared. The mean time interval between scans was 6.1 ± 2.4 years and 4.8 ± 1.7 years in glaucoma and control group

White matter density differences were measured by fiber density (FD), fiber bundle cross-section (FC) and their combination (FDC), and were compared to 14 age-matched controls. Retinal nerve fiber layer (RNFL) changes were evaluated by laser polarimetry. Visual fields in the glaucoma group were assessed by HVF with early to advanced stages of loss noted. The control group was evaluated by FDT. The average of right and left eye RNFL and visual field parameters were used to assess clinical changes.

In this pilot study, no significant correlation of MRI with clinical findings was observed and thus the relationship of MRI findings to glaucoma disease progression is uncertain. The authors reported a significant decrease in FD in the right optic tract and both optic radiations, however no significant changes to the left optic tract were noted. Studies of the lateral geniculate nucleus (LGN), the relay station between these tracts and radiations, may add context to the findings, given that earlier neuroimaging studies have shown significant LGN neural degeneration in glaucoma patients.1,2

Future studies with increased sample size, more sensitive RNFL assessment with OCT, measurement of visual field damage at multiple time points, and information regarding glaucoma treatment received may allow more accurate assessment of glaucoma progression. Longitudinal MRI assessment with optimized methods at additional time points may also help to understand central visual system findings in relation to the clinical course of disease.

The concept of a lag of transsynaptic degeneration lends itself to a discussion of potential neuroprotective drugs to protect against visual system degeneration

Transsynaptic degeneration of the central visual system is well described in experimental primate glaucoma.3,4,5 The concept of a lag of transsynaptic degeneration lends itself to a discussion of potential neuroprotective drugs to protect against visual system degeneration. Indeed, memantine has been shown to attenuate both neuron atrophy6 and dendritic shrinkage in this model.7 At this time, lowering intraocular pressure remains the cornerstone of treatment to reduce the risk of progressive visual system degeneration in glaucoma.8

References

  1. N Gupta, G Greenberg, L Noel de Tilly, B Gray, M Polemidiotis, YH Yucel. (2009). Atrophy of the lateral geniculate nucleus in human glaucoma detected by magnetic resonance imaging. British Journal of Ophthalmology. 93(1): 56-60.
  2. N Gupta, L-C Ang, L Noel de Tilly, Y H Yucel. (2006). Human glaucoma and neural degeneration in intracranial optic nerve, lateral geniculate nucleus and visual cortex of the brain. British Journal of Ophthalmology. 90(6): 674-678.
  3. Yucel YH, Zhang Q, Gupta N, Kaufman PL, Weinreb RN. (2000). Loss of Neurons in Magnocellular and Parvocellular Layers of the Lateral Geniculate Nucleus in Glaucoma. Arch Ophthalmol. 118(3):378-384
  4. Weber AJ, Chen H, Hubbard WC, Kaufman PL. (2000) Experimental glaucoma and cell size, density, and number in the primate lateral geniculate nucleus. Invest Ophthalmol Vis Sci. May;41(6):1370-9. PMID: 10798652.
  5. Yucel YH, Zhang Q, Weinreb RN, Kaufman PL, Gupta N. (2003) Effects of retinal ganglion cell loss on magno-, parvo-, koniocellular pathways in the lateral geniculate nucleus and visual cortex in glaucoma. Prog Retin Eye Res. 22(4):465-81
  6. YH Yucel, N Gupta, Q Zhang, AP Mizisin, MW Kalichman, RN Weinreb. (2006). Memantine protects neurons from shrinkage in the lateral geniculate nucleus in experimental glaucoma. Archives of Ophthalmology. 124(2): 217-225.
  7. Ly, N Gupta, RN Weinreb, PL Kaufman, YH Yucel. (2011). Dendrite Plasticity of the Lateral Geniculate Nucleus in Primate Glaucoma. Vision Research. 51(2): 243-50.
  8. Garway-Heath DF, Crabb DP, Bunce C, Lascaratos G, Amalfitano F, Anand N, Azuara-Blanco A, Bourne RR, Broadway DC, Cunliffe IA, Diamond JP, Fraser SG, Ho TA, Martin KR, McNaught AI, Negi A, Patel K, Russell RA, Shah A, Spry PG, Suzuki K, White ET, Wormald RP, Xing W, Zeyen TG. (2015) Latanoprost for open-angle glaucoma (UKGTS): a randomised, multicentre, placebo-controlled trial. Lancet. 385(9975):1295-304.

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