Intraocular tumors are rare causes of glaucoma. In cases of unexplained glaucoma, the possibility of an ocular tumor must be considered because of the dire consequences of a missed diagnosis. The epidemiology, prognosis, and mechanism of action depend on the specific tumor type. The tumor may not be directly visible in some instances, and different methods of indirect visualization may need to be used.
There are a number of different mechanisms by which ocular tumors can cause glaucoma: (1) direct invasion, (2) pigment dispersion, (3) melanophagic, (4) hemolytic, (5) uveitic, (6) secondary angle closure, (7) iris neovascularization, (8) choroidal detachment, (9) suprachoroidal hemorrhage, and (10) anterior displacement of lens-iris diaphragm.
Mechanisms of elevated intraocular pressure in intraocular malignant melanoma, which is the most common intraocular tumor causing secondary glaucoma, include the following:
Melanoma arising within the iris
Direct growth of the tumor into the angle
Tumor seeding into the angle
Pigment release into the anterior chamber and into the angle
Melanoma arising within the ciliary body
Melanoma arising within the choroid
Neovascularization of the angle
Anterior displacement of lens-iris diaphragm with angle closure
Hemorrhage with volume effect or angle closure
Spontaneous necrosis causing uveitis and secondary glaucoma
Tumor seeding into the chamber angle
Pigment release into the aqueous, the surface of the iris, and the chamber angle
Although individual rates vary, Shields et al showed a 5% incidence of increased intraocular pressure due to intraocular tumors in a series of 2597 patients with ocular tumors.  This is in contrast to 50% incidence of increased intraocular pressure in eyes enucleated for tumors. Incidence of increased intraocular pressure also is dependent on location. Reports indicate a 17% incidence of glaucoma in ciliary body melanoma, 7% in iris melanoma, and 2% in choroidal melanoma. Given the relative infrequency of intraocular tumors, secondary glaucoma as a result of intraocular tumors is a rare event.
Early detection of malignant melanoma of the choroid is critical because a delayed diagnosis may lead to mortality from metastatic disease.