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Medical Forum / General / Vision / September 2005Macugen's black bubble.
When Macugen is injected into the vitreous, an air bubble is sometimes also injected. The bubble appears black and appears to float around quite quickly. (Not like moving around through a gel). Why? Don W. > When Macugen is injected into the vitreous, an air bubble is sometimes > also injected. The bubble appears black Light diverts around the bubble and leaves a relative shadow. >and appears to float around quite quickly. One reason is it was injected with some amount of liquid vehicle. Another reason is the vitreous degrades with age, breaking up into pockets of liquid (lacunae) and coalesced fibrous material (floaters.) -MT >> When Macugen is injected into the vitreous, an air bubble is sometimes >> also injected. The bubble appears black > > Light diverts around the bubble and leaves a relative shadow. I would almost assume that the bubble is a low index of refraction object suspended in a higher index of refraction medium. Therefor (question) lens optics dictates it leaves a shadow? Where do the incident light rays go?? Don W PS. You owe me. You are right that a gas bubble has *way* lower index than the surrounding liquid and/or gel, so the roughly spherical "lens" it forms would be strongly minus, so most incident rays (excepting a few axial rays) are refracted at relatively large angles away from their optical axes. Hence, a "shadow" on the retina. w.stacy, o.d. >>>When Macugen is injected into the vitreous, an air bubble is sometimes >>>also injected. The bubble appears black [quoted text clipped - 8 lines] > > PS. You owe me. Thanks you. Talked to a person that had retinal surgery where a bubble was used to constrain the retina. His bubble "appeared gray". Same logic I am assuming. But here's my kicker question. The Macugen is injected into the anterior of the vitreous. Very quickly, after the shot, the bubble freely moves about. Like not suspended or stuck in a gel, but in a liquid. It moves with head and eye position. How does it (appear to) get out of the gel so quickly????? We're talking elder gels : ) Don W > You are right that a gas bubble has *way* lower index than the surrounding > liquid and/or gel, so the roughly spherical "lens" it forms would be [quoted text clipped - 17 lines] >> >> PS. You owe me. Very quickly, after the shot, the bubble freely > moves about. Like not suspended or stuck in a gel, but in a liquid. It > moves with head and eye position. How does it (appear to) get out of the > gel so quickly????? We're talking elder gels : ) When the (elder) vitreous contracts and detaches, it moves forward, since it is more firmly attached at the front of the eye, leaving behind a space that is filled with an aqueous fluid, which is where the bubble is free to move. w.stacy, o.d. > When the (elder) vitreous contracts and detaches, it moves forward, since > it is more firmly attached at the front of the eye, leaving behind a space > that is filled with an aqueous fluid, which is where the bubble is free to > move. So the big question is how did it get out of the vitreous gel, where it is presumably injected (front of the eye) into the posterior aqueous fluid???? I seem to have a problem in understanding that transistion. I don't see (hmmm) the gel doing that, that quickly. Don W. Take a look at the picture just below the normal schematic to see what I mean, after clicking on: http://www.vitreousfloaters.com/pages/1/index.htm I assume the injection was made in the pars plana area, which is really more the "side" of the eye than the "front" of the eye, and the posterior segment is quite reachable from there... w.stacy, o.d. >>When the (elder) vitreous contracts and detaches, it moves forward, since >>it is more firmly attached at the front of the eye, leaving behind a space [quoted text clipped - 10 lines] > > I assume the injection was made in the pars plana area, which is really more the "side" of the eye than the "front" of the eye, and the posterior segment is quite reachable from there... w.stacy, o.d. Please excuse my delay. Assuming the radius of the cornea is R. The injection sites are at (approximately) 0.3R and at 0.7R (at about 7 o'clock) for the numbing shot and the Macugen off the cornea into the conjunctiva. Don W. They do go through the conjunctiva to get to the pars plana, which is the normal route, and from there, through the sclera and into the posterior vitreous. I don't think anyone touches the cornea for this procedure. w.stacy, o.d. > I assume the injection was made in the pars plana area, which is > really more the "side" of the eye than the "front" of the eye, and the [quoted text clipped - 10 lines] > > They do go through the conjunctiva to get to the pars plana, which is the normal route, and from there, through the sclera and into the posterior vitreous. I don't think anyone touches the cornea for this procedure. My 0.3R and 0.7R are dimensions outside the outer rim of cornea into the conjunctiva. Sorry to use confusing nomenclature. Don W |
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