46.1 Features
Dellaporta first clinically described hypotony and reduced vision following glaucoma procedures or perforating eye injuries in 1954. Years later, Gass used the term “hypotony maculopathy” to highlight the macular changes and visual dysfunction sometimes present in eyes with hypotony. Reduced intraocular pressure (IOP) can cause decreased central vision as a result of folding in the choroid, neurosensory retina, and the retinal pigment epithelium (RPE). As hypotony develops, the outer sclera becomes edematous, resulting in a corresponding reduction to the inner surface area of the eye wall. That compression or reduction of inner scleral size causes the inner choroid and retinal layers to undulate and leads to vision loss (▶ Fig. 46.1). Causes of hypotony can be from decreased aqueous production such as in severe inflammatory conditions or from increased aqueous outflow due to a number of conditions such as wound leak, overfiltration after glaucoma surgery, or cyclodialysis clefts. Hypotony maculopathy is reported in 10 to 20% of cases of glaucoma filtering surgery with an increased incidence seen after the introduction of antimetabolites, particularly mitomycin C. In addition to delayed wound healing and greater risk of wound leak, mitomycin C has been found to be toxic to the ciliary body, causing decreased aqueous production. Risk factors also include younger age, myopia, and male gender. It is believed that the reduced scleral rigidity found in young and myopic eyes facilitates the inward collapse of the scleral wall during hypotony. Choroidal effusion and diabetes have been found to be associated with decreased risk of developing hypotony maculopathy.
Fig. 46.1 Fundus photograph of an eye with hypotony maculopathy, showing radial chorioretinal folds, mild optic nerve edema, and tortuous vessels in the posterior pole.
46.1.1 Common Symptoms
Decreased central vision and metamorphopsia are common. Choroidal thickening and retinal folds can cause relative hyperopia due to axial shortening of the eye. Mild anatomical changes can be asymptomatic.
46.1.2 Exam Findings
Hypotony or recent hypotony is a requisite finding for diagnosis. There is no consensus definition, and upper limits of 5 to 9 mm of Hg have been used in clinical studies. The true definition of hypotony should be any value that causes characteristic functional and structural changes. In rare cases, hypotony maculopathy features may be seen with a “relative hypotony” after a sudden reduction of the IOP to low normal levels from significantly higher levels.
Choroidal/chorioretinal folds in the posterior pole are the characteristic examination finding. The folds are usually broad, have yellow crests with dark narrow troughs, and most often radiate outward from the optic disc and usually appear in a stellate pattern around the fovea, though sometimes their orientation can be random. In long-standing cases of low IOP, the pigmented lines from RPE migration and hyperplasia may persist even after the resolution of the hypotony. Optic nerve edema is sometimes present due to anterior bowing of the lamina cribrosa and subsequent reduction of axoplasmic transport. Vascular tortuosity with or without vascular engorgement can be seen. Cystoid macular edema is a rare finding.
46.2 Key Diagnostic Tests and Findings
46.2.1 Optical Coherence Tomography
Demonstrates choroidal/chorioretinal folds, including subtle alterations demonstrated as undulating Bruch’s membrane/RPE. In addition, intraretinal fluid and/or subretinal fluid may also be occasionally identified. Review all radial or cube line scans as the orientation of chorioretinal folds can be found in any axis (▶ Fig. 46.2).
Fig. 46.2 (a,b) Optical coherence tomography of hypotony maculopathy, showing prominent chorioretinal folds.
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