| Identifier |
post_fixation_blindness_lee_novel |
| Title |
Post Fixation Blindness |
| Creator |
Andrew G. Lee, MD; Sowmya Yennam |
| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (SY) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Subject |
Chiasmal Compression; Convergence |
| Description |
Summary • Pathophysiology of post fixation blindness: o Chiasmal compression of the nasal crossing fiber of the optic nerve (e.g., by a pituitary adenoma) o Bitemporal hemianopsia: temporal fields are lost due to chiasmal compression o Loss of convergence at near > Nasal field typically overlaps with the temporal field > With loss of temporal field, no convergence and no nasal field past fixation point • Clinical manifestation: o When fixing on far objects: > Central vision and visual acuity unaffected > Blind temporally, as expected o When fixing on near objects: > Cannot see beyond fixation point > Blind in a triangle extending out from point of fixation • Clinical implication: o Evaluate patient for bitemporal hemianopsia • Bitemporal hemianopia can also cause nonparetic diplopia, which is discussed in another video. |
| Transcript |
Today we are going to be talking about post fixation blindness, which sounds like a very scary thing but is relatively simple. As you know, when you have a chiasmal compression of the nasal crossing fiber, at the chiasm, like a pituitary adenoma, it can produce a field defect. And the prototype is the bitemporal hemianopsia - bitemporal. In addition to the visual field problem, the bitemporal hemianopsia can produce nonparetic diplopia - and you can watch that video. That nonparetic diplopia is because we have double vision created by breakdown of our fusion because the two intact nasal hemifield are not overlapping. So, the nasal field of one eye overlaps with the temporal field of the fellow eye. And if you have just two nasal hemispheres juxtaposed together, then they might slide. And that slide can cause the diplopia, even though the ductions and versions are full. That is a nonparetic diplopia: an efferent problem created by an afferent problem. That is not what we're talking about today. Today we're talking about post fixation blindness. And so, when you normally have your two visual fields, as I said the nasal field overlaps with the temporal field but what if your temporal field is out? You still have two nasal fields that are fine and if you're looking at a target at infinity, the only thing that will happen to you is you'll bump into things that are in your blind temporal field, but your center vision will be fine. You'll be 20/20. You might not even notice the bitemporal. But once you start looking at something close, at near, now the target is at near. You can still see with the two nasal fields, but this blind temporal field here is going to cause a very strange phenomenon. Because the two blind temporal fields are now here, you can't see beyond this fixation point. So that post fixation blindness will create a new scotoma, but only at near and only in that triangle extending out from the fixation point. Because the two temporal fields are out when you converge at near, you no longer have the nasal field past this point created by convergence. And that is what we call post fixation blindness. So, the patient will be blind in a triangle extending out from the point of fixation but only at near. And that person should be evaluated for a bitemporal hemianopsia. So, both post fixation blindness and nonparetic diplopia arise from the bitemporal hemianopsia. |
| Date |
2021-04 |
| Language |
eng |
| Format |
video/mp4 |
| Type |
Image/MovingImage |
| Collection |
Neuro-Ophthalmology Virtual Education Library: Andrew G. Lee Collection: https://novel.utah.edu/Lee/ |
| Publisher |
North American Neuro-Ophthalmology Society |
| Holding Institution |
Spencer S. Eccles Health Sciences Library, University of Utah, 10 N 1900 E SLC, UT 84112-5890 |
| Rights Management |
Copyright 2019. For further information regarding the rights to this collection, please visit: https://NOVEL.utah.edu/about/copyright |
| ARK |
ark:/87278/s65t9h4r |
| Setname |
ehsl_novel_lee |
| ID |
1680618 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s65t9h4r |
