I had to memorize this for med school exams T_TWhat is Glaucoma?
A group of disorders characterized by progressive optic neuropathy resulting in characteristic appearance of optic disc & a specific pattern of irreversible visual field defects that are associated frequently but invariably with raised intraocular pressure (IOP).
(Simply put, optic nerve fibres are damaged in glaucoma making the optic disc look funny & causes vision loss. It may or may not be associated with raised pressure in the eye.)
Loss of nerve fibres causes visual field defects & optic disc changes in glaucoma.
This blog post covers visual field defects =)
Mnemonic: IC BB Wings & SAD Steps
Before I begin, here are some terminology and definitions you must understand -
What is fixation?
Part of the visual field corresponding to the fovea centralis.
What is central field?
Portion of the visual field within 30° of fixation.
What is Bjerrum’s area (arcuate area)?
That portion of the central field extending from the blind spot and arching above or below fixation in a broadening path to end at the horizontal raphe nasal to fixation. Bjerrum’s area usually is considered to be within the central 25° of visual field.
Now that you’re ready, let’s begin! =)
Visual field defects are initially observed in Bjerrums area & correlate with optic disc changes.
Here’s how the natural history of glacomatous visual field loss goes -
Isopter Contraction (IC): Mild & generalized constriction of central & peripheral field.
Baring of Blind spot (BB):
Exclusion of blind spot from the field.
Small wing shaped paracentral scotoma (Wings): Small discrete scotomas occur in Bjerrums area within central 10°
Siedel’s scotoma (S):
Comma shaped extension of blind spot. (Basically, the paracentral scotoma joins with the blind spot to form a sickle shape scotoma called Seidel’s scotoma!)
Arcuate or Bjerrum’s scotoma (A): Loss of arcuate nerve fibers leads to a scotoma that starts at or near the blind spot, arches around the point of fixation, and terminates abruptly at the nasal horizontal meridian. (That means you can’t see Bjerrum’s area at all!)
Arcuate or Bjerrum’s scotoma
Double arcuate or ring shaped scotoma (D): It develops when two arcuate scotomas join.
Roenne’s central nasal step (Steps): Because of the anatomy of the horizontal raphe, all complete arcuate scotomas end at the nasal horizontal meridian. A step like defect along the horizontal meridian results from asymmetric loss of nerve fiber bundles in the superior and inferior hemifields. (Two arcuate scotomas run in different arcs and meet to form a sharp right angled defect in the horizontal meridian!)
Roenne’s central nasal step
Peripheral nasal step of Roenne’s (Steps): Similar to the above defect, unequal contraction of peripheral isopter leads to this step xD
You need to treat the glaucoma or else the visual field loss will spread & eventually a small island of central tubular vision & a temporal island (more resistant to damage) will be all that is left.
Happy children’s day everyone!
Keep celebrating the child inside of you <3
About the diagrams: I randomly made them for my reference. The isopters & shapes are not accurate but acceptable for understanding what the visual field defects & nerve fibre overlay looks like. However, I do recommend that you refer to another source for appropriate diagrams =)