Determination of the Optic Disc Cupping in Glaucoma

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Determination of the Optic Disc Cupping in
Glaucoma

• Syed S. Hasnain M.D.
• 560 W. Putman Ave 6
• Porterville CA 93257, U.S.A.
• www.hasnaineye.com
• Emailhasnain40_at_sbcglobal.net

Author has no financial interest in this
presentation.
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Purpose

• The term cupping implies that the physiological
  cup begins enlarging in glaucoma.
• The terms cupping and simple glaucoma have been
  synonymous since the 1850s.
• This presentation is to determine whether or not
  cupping is occurring. If it is not cupping, then
  what may be occurring to the physiological cup?
• The methods section discusses three puzzling
  questions and how their answers by deductive
  reasoning and photographic evidence led to the
  conclusion that the optic disc may not be
  cupping, but instead sinking in its entirety.

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Methods Three Puzzling Questions in Glaucoma

• Question 1 Why do some patients develop glaucoma
  at a normal IOP such as 15mmHg, while others do
  not at a high IOP such as 30mmHg?
• Question 2 Why are the arcuate fibers
  selectively destroyed first, whereas the macular
  fibers last until the end stage of glaucoma?
• Question 3 Why cant we halt glaucoma in spite
  of maximally lowering of IOP with treatment?

Answers to the above questions are discussed in
this presentation.
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Discussion Puzzling Question 1Why do some
patients develop glaucoma at a normal IOP such as
15mmHg (NTG), while others dont at a high IOP
such as 30mmHg (Ocular Hypertension)?

• Medical history revealed that HTG patients were
  usually in good health, whereas the NTG patients
  had cardio-pulmonary and circulatory problems.
  Furthermore, about 70 of NTG patients were
  smokers.
• Findings suggest that NTG may be a systemic
  disease and glaucoma a multifactorial disease.
  Glaucoma being a multifactorial disease may be
  the answer to question 1. More the risk factors
  present, higher the likelihood of development of
  glaucoma.
• This raises another question If HTG is an ocular
  disease, whereas NTG a systemic disease, then why
  are the arcuate field defects present in both
  cases? If glaucoma is a multifactorial disease,
  then there should be a common site of injury
  somewhere in the course of pathogenesis of both
  HTG and NTG.
• Since arcuate fibers are destroyed in both HTG
  and NTG, the pursuit of their pathogenesis may
  lead to a common site of injury.

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Discussion Puzzling Question 2 Can the
arcuate fibers in the disc or in retina be
selectively destroyed by any pathology ?

• Not likely. How is it possible that high IOP, or
  any other pathology, can selectively and
  precisely destroy only the arcuate fibers among
  the one million or so densely packed nerve fibers
  in the optic disc? If this is not possible, then
  the optic disc may not be the primary site of
  injury.
• How is it possible that high IOP, or any other
  pathology, can selectively and precisely destroy
  only the arcuate fibers of the retina? If this
  is not possible, then the retina may not be the
  primary site of injury.
• Regarding apoptosis How is it possible that
  apoptosis in glaucoma will initiate selectively
  with only those ganglion cells
• of retina which serve the arcuate fibers? If
  this is not possible, then apoptosis of the
  ganglion cells may not be occurring.
• If the disc or retina is not the primary site of
  injury, then what may be the primary site of
  injury? We are left with the circular border
  tissue which we will discuss in next slide.

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Discussion Can the border tissue be the common
site of injury?

• Circular border tissue lies between the optic
  disc and scleral rim and secures the disc in the
  scleral opening.
• Border tissue is exclusively supplied by short
  posterior ciliary arteries (ciliary circulation).
  Ciliary circulation is a low pressure system due
  to its multiple branches as compared to the CRA
  which mainly remains solitary from its origin.
• IOP and arterial pressure are opposing forces.
• Normally, IOP should be lower than the arterial
  pressure of the border tissue for its healthy
  maintenance.
• The above circulatory balance would be reversed
  due to either an increase in IOP or decrease in
  arterial pressure resulting from poor systemic
  circulation. In the latter scenario, even normal
  IOP would become high for that particular eye and
  would compress the already weak circulation of
  the border tissue. This would result in chronic
  ischemia and atrophy of border tissue and thus
  sinking of optic disc.

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Discussion Can the arcuate fibers be
selectively destroyed if optic disc is sinking?

• Likely. As the border tissue atrophies, the optic
  disc would become loose and begin to sink.
• Since the optic disc usually has an oblique entry
  in the globe, the temporal part is more closer to
  the scleral edge (rim).
• As the disc sinks, all temporal fibers (superior,
  inferior arcuate, and macular) would be stretched
  and severed at the scleral rim. However, since
  the arcuate fibers are fewer in number, they
  would be depleted earlier, giving rise to double
  arcuate field defects, whereas the macular fibers
  being abundant would last until the end stage of
  glaucoma. This may be the answer to question 2
  that why are the arcuate fibers selectively
  destroyed?

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Results Optic disc may be sinking as it can
explain the production of arcuate field defects
Temporal sinking would result in severing of the
macular and sup. inf. arcuate fibers. However
since arcuate fibers (blue) are fewer in number
they would be depleted earlier, giving rise to
double arcuate field defects whereas the macular
fibers being abundant would last until the
end-stage.
Double arcuate field defect on perimetry
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Early and Late Stage Glaucomatous Discs Patients
A B
Late stage left eye of same patient A
Physiological cup is broken due to confluence of
cup pallor with the pallor produced by the
destruction of nerve fibers in the peripheral
part. Marked kinking of blood vessels at disc
margin due to loss of underneath nerve fibers.
Patient A Early stage Right eye No change in
contour of the physiological cup. Prominent
scleral edge due to thinning of RNFL from
severing and depletion. Sloping of blood vessels
due to sinking disc. splinter hemorrhage at
7oclock due to severing of smaller blood vessel.
Patient B Early stage Right eye No change in
the contour of physiological cup. Prominent
scleral edge due to thinning of RNFL. Sloping of
blood vessels due to sinking of disc.
Late stage left eye of same patient B.
Physiological cup is obliterated. Marked kinking
of blood vessels at disc margin due to loss of
underneath nerve fibers.
Pa
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Analogy Sinking manhole cover to a glaucomatous
disc
Normal Manhole cover flush with the road. Blood
vessels are straight at the margin of the disc.
If there is no sloping or kinking of blood vessel
at the margin, then there is no sinking of the
disc and probably no glaucoma.
Early stage glaucoma Physiological cup is still
intact. Splinter hemorrhage at 7 oclock. Kinking
and sloping of the blood vessels. Arcuate field
defect present. Temporal part pale and sunken due
to thinning of RNFL.
Late stage glaucoma Physiological cup is broken
due to confluence of cup pallor with pallor
produced by the destruction of nerve fibers in
the peripheral part. Nasal shifting of vessels
from loss of anchorage due to earlier thinning
of temporal RNFL as compared to that of nasal
RNFL.
End stage glaucoma Total loss of the optic disc
due to axotomy of the axons. Disc area becomes
an empty crater. Only the larger blood vessels
remain.
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What happens as the sinking of the disc
continues?

• 360 degrees of retinal nerve fibers anchor the
  optic disc in place as roots anchor a tree.
• As the nerve fibers are being severed and
  depleted, the optic disc would become more loose
  and sinks further, resulting in severing of more
  nerve fibers. This is revealed by OCT
  progressive thinning of the RNFL.
• Severing of the nerve fibers creates a
  self-propagating cascade of loosening and sinking
  of the disc which would continue until all the
  nerve fibers are severed at the edge. This may be
  the answer to question 3 that once glaucoma is
  initiated it cannot be halted.
• At the end-stage, unlike any other disease, there
  is no optic disc and no nerve fibers. This is
  revealed by the histology of the end-stage
  glaucomatous disc an empty crater.

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Conclusion

• Physiological cup may not be enlarging but
  breaking up (obliterating). Cupping
  occurring concentrically cant explain arcuate
  field defects.
• Fibers for the central vision are located in the
  central part of the disc and superficial (closer
  to the vitreous). Therefore, if cupping were
  occurring, then the central fibers should have
  been destroyed first but this is not the case
  because the central vision fibers are destroyed
  last in glaucoma.
• In sinking, the peripheral fibers would be
  severed first because they lie deeper in close
  proximity to the scleral rim, whereas the central
  and superficial fibers last - this is what is
  occurring as revealed in glaucomatous field
  defects.
• Continuous severing of prelaminer fibers due to
  continuous sinking of disc would result in
  progressive thinning of the RNFL this is what
  revealed by OCT.
• At the end-stage, the disc area is replaced with
  an empty crater due to severance (axotomy) of all
  the axons of the optic disc this is what
  revealed by end-stage histology.