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    How low is too low?

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    Though rare, hypotony after cataract surgery can occur. The ability to recognize common causes of low IOP postoperatively can aid in its prevention and management.

     

    Baltimore—Postoperative hypotony is a problem not often seen by ophthalmologists, but when it occurs, elucidating its exact cause and treating it properly is imperative.

    “Hypotony after cataract surgery is rare, but it can occur,” said Dr. Weinberg, chairman of ophthalmology, Johns Hopkins Bayview Medical Center, Baltimore. “We don’t talk about hypotony and low pressure very often, but I think we should all be thinking about this topic. When we’re closing cataract wounds, we are obviously concerned about pressures at the end of the procedures, but we should remember postop pressures as well.”

    Dr. Weinberg

    Hypotony is defined as low IOP (≤5 mm Hg) that can be acute, transient, chronic, or permanent, and can lead to functional changes (asymptomatic or symptomatic) and structural changes (reversible or irreversible) over time.

    “The question is: ‘How low is too low?’ Low pressures can sometimes be asymptomatic, and not all chronically low IOPs lead to irreversible vision loss,” Dr. Weinberg said. “But low IOP and poor visual acuity may have obvious correlates.”

    Hypotony can be defined in terms of time, as acute, transient, finite, prolonged, or persistent.

    “It is the persistent hypotony that we want to try to avoid, because there are irreversible structural and functional changes,” he said. “We learned about these early in our residencies.”

    These irreversible structural changes can include corneal astigmatism, anterior chamber shallowing and flare, macular edema, disc edema, and choroidal detachment. Corneal edema is also a possibility, he added.

    Causes of low IOP

    Normal IOP depends on adequate aqueous production, an intact corneoscleral wall, attachment of the uvea, integrity of the pars plana and choroidal attachment, and the absence of retinal holes and inflammation.

    The most common cause of postoperative hypotony after cataract extraction is a non-healing or leaking cataract wound. Internal fistulas can occur, connecting the aqueous or the vitreous to the suprachoroidal space and can be caused by a cyclodialysis or a retinal hole. Other causes of hypotony also can include ciliary body insufficiency, continued Dr. Weinberg, which can lead to ciliary body detachment.

    In addition, inflammation can cause decreased aqueous production and low IOPs as well, he added. Non-surgical causes of hypotony include ocular ischemia, dehydration, acidosis, anemia, and myotonic dystrophy.

    Treatment of hypotony

    “How do we treat hypotony? Obviously, the best treatment is prevention,” Dr. Weinberg continued.

    Wound leaks after cataract surgery can be healed with a pressure dressing or bandage contact lens and time, topical adhesive or placement of additional sutures in the wound. If postoperative hypotony does occur, and there is no obvious wound leak, one should look for a cyclodialysis cleft. For cyclodialysis clefts, which may be detectable only on gonioscopy and/or anterior segment imaging, treatment consists of diathermy, cryotherapy, laser application to the cleft, or surgical re-attachment.

    For significant postoperative inflammation, cycloplegia or corticosteroids should be used.

    “In certain patients who have had vitrectomy, cataract detachment, or scleral buckling, I will use a scleral support ring at the time of cataract surgery,” Dr. Weinberg said. “I also like to place those support rings in [patients with] high myopia, younger patients, and in patients with scleral thinning.”

    Surgeons must be aware, however, of the problems that may be associated with scleral support rings, which can include subconjunctival hemorrhage and inadvertent perforation from suture placement—the latter of which can be a cause of postoperative hypotony, he added.


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    Liz Meszaros
    Liz Meszaros is a freelance writer in eastern Pennsylvania.

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