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Slide 1 |
Parisa Farhi, MD
Hypotony is statistically defined as IOP of less than 10.1 mm Hg, which is 2 standard deviations below the mean population IOP of 15.9 mm Hg.1 Clinical hypotony occurs when ocular function is decreased secondary to ocular hypotension. Many clinicians use IOP less than 5 mm Hg to define clinical hypotony.1,2 Hypotony maculopathy occurs when hypotony affects the macula, leading to structural and functional changes.1-4
Dr. Angelos Dellaporta has been credited for describing fundus changes associated with hypotony in 1955.2,5 J. Donald M. Gass, MD, coined the term hypotony maculopathy in 1972.1,2
Associated findings may include ocular shrinkage (with reduction of the axial length and volume of the eye), optic disc swelling, choroidal effusion, retinal or choroidal folds, retinal vascular tortuosity, neuronal atrophy, collapse of the anterior chamber, anterior chamber flare, cataract, corneal edema, astigmatism, and visual acuity decline (Slide 1).1-7
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Indocyanine green angiography (ICG), a study used to evaluate choroidal circulation, may show choroidal vascular dilation and tortuosity in the posterior pole in addition to scattered areas of hypofluorescence.8
Diagnosis is based on findings of a hypotonic eye along with some of the above associated findings. Many authors define hypotony maculopathy by findings of IOP less than 5 mm Hg in addition to retinal/choroidal folds (particularly in the macula), vascular tortuosity, papilledema, and/or vision loss.9 However, hypotony is a relative state. The literature provides one case report of fundus changes suggestive of hypotony maculopathy but with statistically normal IOP in a patient with increased intracranial pressure.3
Optical coherence tomography (OCT) has recently shown potential to be a useful tool to diagnose occult hypotony maculopathy and to assess resolution of this condition.10,11
Hypotony results when the normal pressure of the aqueous and vitreous humor in the eye is compromised. Hypotony may be secondary to one or more of the following:
One of the most common causes of hypotony maculopathy is trabeculectomy. Hypotony maculopathy accounts for 3% to 14.3% of post-trabeculectomy vision loss.1,9 Trabeculectomy is a fistulizing procedure aimed at treating glaucoma by reducing IOP. Antifibrotic agents such as mitomycin C and 5FU are used to decrease fibrosis of the bleb; however, the use of these agents is associated with a higher risk of hypotony maculopathy.6,17-18
In a retrospective study of 81 eyes with hypotony maculopathy, an age of younger than 60 years, myopia, and male gender were found to be significant risk factors for this condition.1 Diabetes and choroidal effusion were associated with a decreased risk of hypotony maculopathy.1 However, in a retrospective study of six patients with hypotony maculopathy, coronary artery disease, and systemic hypertension were associated with higher risk.9
In another retrospective study of 52 eyes, increased time of application of mitomycin C was associated with increased risk of hypotony. Neither age nor number of previous incisional eye surgeries was found to be a significant risk factor for development of hypotony. However, hypotonic eyes were found to have lower preoperative IOPs, on average.19
Normalizing IOP might restore the functional and structural changes caused by hypotony. Treatment is usually initiated when visually significant deterioration occurs.20 For trabeculectomy-induced hypotony, decreasing filtration through the bleb may be curative.6 Bandage soft contact lens or collagen shields, eye patching, topical corticosteroids, tissue adhesives, diathermy, cryotherapy, intraocular perfluoropropane injection, autologous blood injection, trichloroacetic acid use, argon or neodymium:YAG laser-induced subconjunctival bleeding, argon photocoagulation of the surface of the bleb, intracameral viscoelastic injection, compression sutures, patch grafting the sclerostomy site, and cataract surgery are techniques used with variable success to treat an eye with post-trabeculectomy hypotony.6,10,18,20,21
For cases of cyclodialysis-induced hypotony, cycloplegia, argon laser trans-corneal photocoagulation, and transscleral cyclophotocoagulation have been used to close the cleft.15 For difficult-to-close clefts, ciliochoroidal argon laser endophotocoagulation, cryotherapy diathermy, translimbal and transscleral suture fixation, direct cyclopexy, anterior scleral buckling, combined vitrectomy, cryotherapy and gas tamponading, and phacoemulcification plus a capsular tension ring placement have been tried.14,15 In cases where normalization of IOP does not correct the structural and functional changes of an eye with hypotony maculopathy, vitrectomy and replacement of the vitreous with an agent that is heavier than water might improve vision.20
Normalization of IOP may or may not correct the structural or functional changes in an eye with hypotony maculopathy.20,23 Cases of significant acuity improvement have been described by normalizing the IOP despite prolonged hypotony maculopathy.24 However, chronic swelling of the retina can lead to damage to the ganglion or photoreceptor cells.3 Therefore, rapid intervention once the diagnosis has been made is advisable.