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Uveal Effusion and Primary Angle Closure Diseases
Hiroshi Sakai (Winner WGA-Award 2005)
Relative pupillary block is considered the most important trigger of the angle closure mechanism in primary angle closure (PAC). However, the pupillary block mechanism is not a really 'primary' mechanism. Relatively short axial length, usually related with hyperopia is a well known anatomical background of PAC. Hyperopia and those with a short axial eye have shallow anterior chamber by nature. PAC is age dependent. Increased lens thickness due to the lens epithelial growth may account for part of the mechanisms of anterior chamber shallowing and increased chance of relative pupillary block mechanism with age. Additionally subclinical uveal effusion has been observed by ultrasound biomicroscope (UBM) in various phases of PAC eyes.1 Is uveal effusion one of the pathogenetic mechanisms of PAC?
In the acute phase of APAC, within 24 hr after initial treatment with IOP of over 40 mmHg, uveal effusion was found in over 50% of the cases. The relationship between malignant glaucoma and (acute) PAC on the one hand, and the relationship between uveal effusion and malignant glaucoma on the other hand is well known. In addition to the acute crisis itself and its medical treatments, surgical interventions, secondary inflammation, and sudden decrease of intraocular pressure might lead to the development of uveal effusion. The effusion may cause anterior rotation of ciliary body and consequently a shallow anterior chamber, resulting in angle closing in malignant glaucoma. Another possibility is that uveal effusion through its volume effect on the vitreous may push the lens forward.2 Angle closure due to uveal effusion is comparable to malignant glaucoma.3 Uveal effusion after acute PAC may not be a cause of the acute PAC, but the result.
At least a part of the effusions in acute PAC eyes, however, may exist before the acute attack and may be a trigger of the acute PAC. The fellow eye of acute PAC or even chronic PAC eyes may show the small effusion (less than 10%).
Detailed UBM examination over the equator of the globe in the circumference of the eyes is necessary to find this type of uveal effusion. However most of the grade 1, slit-like effusions, may not be found by routine UBM examination. Also there is a limitation of the resolution of UBM in clinical use. If the resolution of the equipment were higher, we may find more slight accumulation of the fluid over the ciliary body or choroid in PAC eyes.
But, is such a small uveal effusion significant? The answer is yes. The central anterior chamber depth in chronic PAC eyes with uveal effusion is shallower than that without uveal effusion. Casual relationship between uveal effusion and anterior chamber shallowness is already known in several conditions such as uveitis. Subclinical uveal effusion in PAC eyes, even if most of them are slight, might play an important role in progressive shallowing of the anterior chamber resulting in increased relative pupillary block and PAC. Small uveal effusion in PAC may not be an independent or direct angle closing mechanism similar to pupillary block, but induces the pupillary block in same manner as a thickened and forward displaced lens.
Interestingly, the effusion in chronic PAC occurs in phakic eyes, and in PAC eyes that had already undergone cataract surgery. Uveal effusion and increased lens thickness and/or forward displacement of the lens may affect each other. The Zonules of Zinn are anchoring the lens to the ciliary body not only on pars plicata but also on pars plana. The tension of the zonules onto the pars plana of the ciliary body may affect the development of the effusion. Thus the lens may be the primary factor of the progression of shallow anterior chamber depth in PAC by its volume itself and by the development of the uveal effusion.
References
- Sakai H, Morine-Shinjyo S, Shinzato M, Nakamura Y, Sakai M, Sawaguchi S. Uveal effusion in primary angle-closure glaucoma. Ophthalmology 2005;112:413-419
- Quigley HA, Friedman DS, Congdon NG. Possible mechanisms of primary angle-closure and malignant glaucoma. J Glaucoma 2003;12:167-180
- Liebmann JM, Weinreb RN, Ritch R. Angle-closure glaucoma associated with occult annular ciliary body detachment. Arch Ophthalmol 1998;116:731-735.