The most puzzling question in glaucoma which is rarely discussed: one million or so densely packed nerve fibers (NFs) in the ONH are being destroyed in an orderly sequence from peripheral to central, never haphazardly or other way around. If this was not true and the results of glaucomatous visual fields were erratic , then we wouldn’t be doing visual fields test in glaucoma.
Cupping concept even if true, should result in loss of central vision first and not the peripheral. Cupping also can’t explain the orderly loss of NFs and the production of initial isolated scotomas in the paracentral area which become more frequent and coalesce to become sharply defined arcuate field defects. Orderly loss of NFs and sharply defined margins of the arcuate field defects will reject all the prevalent glaucoma theories such as cupping, Neurodegeneration, Apoptosis, ischemia, CSF and direct role of IOP on the nerve fibers. If any glaucoma theory can’t explain the orderly loss of NFs and arcuate field defects is redundant and is of no value.
Can proponents of the neurodegenerative theory can explain the orderly loss of NFs which is the most pathognomonic feature of glaucoma?
I was under the impression that the ipRGC cells die off first. That will affect a sleeping pattern, which in turn affects energy levels, and thus body biochemistry and perhaps that triggers a cascade of events for the orderly changes. Is that whas you heard?
The most puzzling question in glaucoma is: one million or so densely packed nerve fibers in the ONH are being destroyed, one by one, in an orderly sequence and never, never haphazardly. It is a mystery which needs to be resolved.
It is so strange and unbelievable that we have never taken advantage of such a important lead in finding the true pathogenesis of glaucoma even though we are doing perimetry for over a century for glaucoma diagnosis. It is so sad that we talk about everything in glaucoma but never discuss the cause of orderly loss of NFs!
We will be wasting our time and resources in bringing forward plethora of glaucoma theories if we don’t the address the subject of orderly loss of NFs in these theories.
None of the prevalent glaucoma theories including time honored ‘cupping’ and newly invented ‘neurodegeneration’ can either explain or result in the orderly loss of NFs. In fact, there is no biological mechanism which could lead to the orderly loss of NFs in glaucoma. There has to be some mechanical scenario for the orderly loss of NFs even though that mechanical scenario may have resulted from biological effect of elevated IOP on some important component of ONH.
I will urge researchers to look for the cause of the orderly loss of NFs as this may be the only way we may find the true pathogenesis of glaucoma, in my humble opinion.
Nerve fiber loss not 'orderly' in glaucoma. Variations in the form of paracentral scotoma, seidel/ centrocecal scotoma, arcuate, bjerrum's scotoma etc occur. Thats the reason, early glaucoma difficult to diagnose. Infact, functional changes on visual fields noted much later than the structural changes.
Early defects in glaucoma are notching, bending of vessels(bayoneting), Retinal nerve fiber layer defects, Macular ganglion cell loss etc. It is only when advanced cupping/excavation occurs that central vision lost.
If NFs loss is not orderly in glaucoma then the role of perimetry would be useless. Who would like to do visual fields test in glaucoma if the results would be erratic and unpredictable?
There are about one million NFs densely packed in 1.5 mm optic disc. If elevated IOP was directly destroying the NFs then all the NFs would have destroyed at same time, not in stages lasting over several years in chronic glaucoma. So, elevated IOP must be destroying NFs indirectly- that’s is the mystery which needs to be solved.
It is widely believed that peripheral NFs are destroyed first followed by paracentral area and finally central fibers, never other way around. Although isolated scotomas in the paracentral area don’t follow the perfect pattern but eventually all the isolated scotomas coalesce and result in fully blown double arcuate defects. We never see central field loss first and the peripheral at the end. There is a definitive predictable pattern of glaucomatous field loss whether you agree or not.
We may not have to argue whether the field loss is orderly or not orderly in glaucoma. Also whether glaucoma is an autoimmune or neurodegenerative disease or any other mysterious disease.
But the bottom line is that the NFs in glaucoma are being stretched and broken. There is plenty of evidence of severance of NFs occurring in glaucoma. Researchers can approve or disapprove the severance of NFs easily. If NFs are indeed being severed then glaucoma would be viewed from an entirely different angle.
True.
The consistency being glaucoma field loss respects horizontal meridia. Otherwise, patterns of field loss in glaucoma may be quite varied. And to add to the confusion...the field loss may also be due to retinal pathologies, other neurological diseases, cataract/media opacities, drug toxicity, patient related errors/factors, rim artifacts etc.
Perimetry is just one of the diagnostic tools for glaucoma.
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