Thursday, November 14, 2013

Progression of visual field defects in Glaucoma mnemonic

I had to memorize this for med school exams T_T

What 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

Progression of visual field defects in Glaucoma mnemonic
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.

That's all!

Happy children's day everyone!
Keep celebrating the child inside of you <3

Love,
IkaN

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 =)

Asked through email: Hey IkaN! What does exclusion of blind spot mean?
Answer: Exclusion of blind spot means the blind spot is not included in the area of vision loss.
If there was a pie with a cherry on it and you ate pieces of the pie without eating the cherry, you excluded the cherry from the area of eaten pie (This means the cherry is excluded from the area of food loss xD)
The pie is your field of vision, cherry is the blind spot and if you eat the pie, you can no longer see it, hence the eaten part is the area where there is vision loss.
I'm such a foodie lol. 

47 comments:

  1. thank u very very much

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  2. Thats an awesome presentation... got a clear view.. thanks..

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  3. Awesum.. cn u please gve your email id so that any further doubts cn be cleared?? Thnk u so much

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    1. My email id is: medicowesome@gmail.com
      You can ask doubts in the comments as well :)

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  4. thanks a lot. really saved a lot of time and effort for me

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    1. Yaay! Use the saved time to do something absolutely amazing. My pleasure :)

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  5. I am glad i found your blog! Thanks a ton! This was mother of god! Now I'll stay in touch with your blog! Super cool!

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    1. Haha I know how that feels.. Toughest thing to remember in Opthalmology *sigh*

      Thank you!

      Glad to know you'll stay in touch.. Welcome to Medicowesome :)

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  6. All the best for usmle! Can you tell me the strategies (basic) to prepare for usmle? I'm in my prefinals! :p
    I'm planning to prepare for usmle but somebody told me that they don't give scholarships now to Indians so I dropped the idea.. Is it true? :/

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    1. Thank you! Wish me luck for universities though. Final year exams in 2 weeks *yikes*

      I'll write the post next month, caught up with exams at the moment.

      In super short, Kaplan videos, Goljan audio, uWorld qbank & first aid is the general way to go for step 1.
      I recommend pathoma videos as well.

      Umm you mean scholarships for electives? It depends on the field you are applying for and the colleges you opt.

      The process is costly, but I think you should prepare for the exam anyway. The knowledge you gain is immense.

      And my belief is that, if you have the will, God finds a way for you. So don't let finances stop you from studying! But that's just me.

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    2. Thanks! And ya all the very best! I'll be waiting for your next article.. And plz do write about usmle also in the coming articles.. Thnx a lot! I love your blog! <3

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    3. I'll let you know when I do :)

      Thanks for all the love <3

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  7. thanx for this awesome description and a nice mnem. i like it....

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    1. You're welcome! Glad you liked it :)

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  8. Really useful :-)
    What text do u use to study ophthal ?khurana ?

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  9. Thank u so muchh..it really did help hoardzz

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  10. thank you for giving us your notes; kind of, anyways pnemonics were coool, impressive thankyou

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  11. Thankypu nakeya :)

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  12. Thank u so so much ..helpd me a lot ..please continue this amazing work

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    Replies
    1. You're welcome. Thanks for the compliments. Will try <3

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  13. Expressed in a simple and beautiful manner. Really appreciate the work

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    Replies
    1. Thank you for the compliments :)

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  14. sir thanku very muchhhhhhhh sir plz giv me link for other mnemonics of optha i'm struggling a lot plz hlp me

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    1. You are most welcome! Check out the contents page for more ophthalmology posts :)

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  15. Thank you for the amazing mnemonic :)

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  16. Blog posts help a lot esp when exams are near... thank you sis for such an awesome glaucomatous post!!!

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  17. Thank you so much.. Awesome presentation.. Everything clarified

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