Choroidal osteoma

Choroidal osteoma is a benign tumour of the choroid (the vascular membrane that covers the inside of the eyeball) made up of bone tissue. The rate of incidence is higher in females, Caucasians and young and healthy patients. In general, it only affects one eye and is frequently located near the optic nerve (juxtapapillary region).

In general, it grows very slowly and far from the macula (the central part of the retina) which is why symptoms only occur at the later stages. 

Clinical manifestations include mild blurred vision to a severe loss of vision, plus metarmophpsia (distored vision) and changes to the visual field. 

It's a very rare tumour, the cause of which is still unknown. 

We cannot prevent a choroidal osteoma, but we can diagnose it before its most feared complication arises, the one which has most impact on our eyesight: choroidal neovascular membrane.

We reach the suspected diagnosis by making an in-depth assessment of the back of the eye, where we see a raised lesion with well defined rounded edges, which is yellowy and generally has irregular pigmentary build-up on the surface.

To confirm the diagnosis, we rely on an ecography of the eye where we can detact a choroidal mass with calcium content (bone tissue). Other tests, like a head scan (head CT scan) or head magnetic resonance scan (head MRI) will show the presence of a patch of bone near the optic nerve. 

The importance of its diagnosis lies not so much in diagnosing this lesion per se but rather making a differential diagnosis compared to other malignant tumors of the eyeball that could compromose not just thevision, but also patient survival, as is the case with malignant choroidal melanoma or choroidal metastasis. 

It is also helpful to distinguish it from other diseases and benign tumours that could be potentially serious for the eyesight, such as choroidal hemangioma, central serous choroidopathy, serpiginous choroiditis, etc. 

The visual prognosis is linked to the growth of the tumour and the monitoring of choroidal neovascularisation with which it is frequently associated. 

For the former, there aren't any treatments that are effective enough to prevent the growth of the choroidal osteoma without damaging the surrounding tissue, although on many occasions these tumours do not show any growth or grow very slowly, over decades even.

For neovascular membranes, the treatment of choice is anti-angiogenic intravitreal injections, as it is for other causes of choidal neovascularisation.