exam study question

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what is the mechanism on how cataract surgery can help lower intraocular pressure for glaucoma patients?

 

[MstaKing10]

I believe you are referring to patients with phacomorphic, phacolytic or phacoantigenic glaucoma. In phacomorphic glaucoma, the lens is essentially pushing the iris forward contributing to narrow angle glaucoma. In phacolytic and phacoantigenic glaucoma, lens material induces inflammation and "clogs" the trabecular meshwork leading to increased intraocular pressure. This is very simplistic, perhaps others can expand if necessary.

 

[RestoreSight]

what is the mechanism on how cataract surgery can help lower intraocular pressure for glaucoma patients?

There are a number of studies that show IOP is reduced by 3-4 mmHg following routine phaco cataract surgery. The mechanism is not entirely clear, but increased aqueous outflow through the TM appears to be a central mechanism given the angle width does not change considerably following placement of standard posterior "in-the-bag" IOLs. One theory is that normal aging causes increased width of the lens leading to anterior traction on the zonules anchored to the ciliary body. This tethering inhibits ciliary body contraction and proper opening of the TM reducing outflow. Another theory is local inflammation following cataract extraction leads to reduced IOP production by the ciliary body epithelium. This same effect is documented in cases of uveitis. Another theory is that the relatively high IOP seen in cataract extraction (documented up to 90 mmHg) can increase patency through the TM through SC and into the episcleral vessels. Large bulk flow may act to "open" a previously stenosed outflow tract. This has been artificially demonstrated using drugs that disrupt the cytoskeleton of the TM and/or its contractility which reduce outflow resistance and IOP in bovine and monkey eyes.

I should clarify all of these are hypothetical mechanisms. Data is rather sparce. It is well documented that there is a 3-4 mmHg drop in IOP following cataract surgery, but I don't think its a viable alternative to current anti-glaucoma therapies and surgeries and I don't think its fully understood. Hope this helps.

 

[EyeRegenMed]

what is the mechanism on how cataract surgery can help lower intraocular pressure for glaucoma patients?

An alternate hypothesis is that the phacoemulsification ultrasound energy propagated through the fluid medium induces a stress response with the potential to lower IOP.

Reference:
Ultrasound activates the TM ELAM-1/IL-1/NF-kappaB response: a potential mechanism for intraocular pressure reduction after phacoemulsification.
http://www.ncbi.nlm.nih.gov/pubmed/12714632