The choroid is the pigmented, highly vascular layer of the globe lying between the sclera (on the outside) and the retina (on the inside). It is one of the three components of the uveal tract and is shaped a little like the body of a rounded wine glass. The optic nerve emerges at its base and the other two components of the uveal tract sit anteriorly: the ciliary body lies around the rim and the iris stretches over the opening.
The choroid is made up of three layers, each of which can be affected by disease processes. There is the external vessel layer, the capillary layer and the internal sheet-like Bruch's membrane. The main function of the choroid is to nourish the outer layers of the retina but it is also thought to regulate retinal heat, to assist in the control of intraocular pressure, and the pigment absorbs excess light so avoiding reflection.
See separate article on Choroidal Melanoma.
Choroidal naevi are similar to naevi present in other parts of the body and are probably present at birth, growing mainly in childhood and rarely beyond puberty.
- Epidemiology - choroidal naevi are present in about 5% of the general population - most commonly, in people with dark features.
- Presentation - choroidal naevi tend to be incidental findings. Very occasionally, they may be associated with a retinal detachment and therefore present with symptoms characteristic of this, such as floaters, flashes and visual field defects.
- Investigations - if a choroidal naevi looks suspicious or is thought to have grown during adulthood, then it must be investigated as for a melanoma (see article on Choroidal Melanoma).
- Treatment - typical choroidal naevi do not require any intervention but suspicious lesions are monitored every 3-6 months initially (later every 9-12 months). Fundus photographs are helpful in monitoring changes. Photodynamic therapy has been shown to be effective where the naevus is associated with a retinal detachment.
- Prognosis - choroidal naevi are mostly harmless although a small proportion may be associated with a mild visual loss over many years.
Choroidal haemangioma are uncommon benign vascular tumours of the choroid that can be circumscribed or diffuse. Circumscribed tumours occur sporadically, without any associated local or systemic anomalies. Diffuse choroidal haemangiomas generally occur as a part of the Sturge-Weber syndrome. They may be stationary or fast-growing. Choroidal haemangioma only cause problems when they are located near to the macula (or grow over it) or when they leak, so causing a retinal detachment.
- Presentation - circumscribed choroidal haemangiomas are usually diagnosed between the second to fourth decade of life when they cause visual disturbances as a result of an exudative retinal detachment. Diffuse choroidal haemangiomas are usually evident at birth.
- Investigations - ultrasound scan, fluorescein angiography, MRI.
- Treatment - photodynamic therapy has been used with some success; thermotherapy and radiotherapy are other treatment options. One study showed similar if not better anatomic and visual acuity results for photodynamic therapy compared with thermal laser photocoagulation when treating symptomatic circumscribed choroidal haemangioma.
- Prognosis - visual acuity drops to <6/12 in about 50% of cases (often to 6/60). Treatment is often but not always effective in improving visual acuity.
90% of metastatic disease affecting the uveal tract occurs in the choroid because of its high vascularity.
- Epidemiology - they occur in 2-7% of patients with metastatic cancer. Metastases from breast cancer and lung cancer are particularly common. Other recognised cancers include prostate cancer, gastrointestinal tract cancers, the kidney cancers, skin cancers and leukaemia.
- Presentation - decreased visual acuity (the most common presentation) and, occasionally, diplopia, photophobia, blepharitis, pain, secondary glaucoma, exophthalmos and a detached retina may occur. It may be an incidental finding.
- Investigations - ultrasound scan, fluorescein angiography, biopsy and systemic investigations (blood tests and imaging).
- Treatment - this may range from observation (if the patient is asymptomatic and already on systemic treatment) to any of the treatments outlined above for choroidal melanoma (including enucleation for the painful, blind eye), depending on the nature of the lesions. Radiotherapy is a commonly used modality which, in many cases, enables patients to maintain useful vision for the remainder of their lives.
- Prognosis - this depends on the underlying cancer.
Choroidal osseous choristoma is a rare, slow-growing benign tumour which progressively calcifies and ossifies. It occurs in both eyes in about 25% of cases with asymmetrical disease progression. Visual impairment occurs as a result of the damage to the retina overlying the lesion.
- Epidemiology - 90% of the patients affected are young women.
- Presentation - gradual visual impairment in the second to third decade of life.
- Investigations - ultrasound scan, fluorescein angiography.
- Treatment - the tumour itself does not need treatment but associated overlying retinal changes may require laser treatment.
- Prognosis - this depends on the site of the lesion: if it lies over the macula, it can be sight-threatening.
- This deeply pigmented tumour often occurs near the nerve head. It is generally benign and needs no treatment but may very occasionally undergo malignant transformation.
- The more common problem with these tumours is local growth affecting adjacent tissues. This can produce afferent pupillary defects (30%), subretinal fluid (10%) and an enlarged blind spot (75%).
- There are few treatment options available in the event of growth but enucleation may need to be considered for extreme growth. These lesions must be monitored for malignant transformation.
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