Shiraz Qureshi Shafi
Introduction
Choroidal osteoma is an uncommon benign intraocular tumour characterised by the formation of mature bone within the choroid. First described in the late 20th century. It remains a rare diagnosis in ophthalmology. Despite its benign nature, choroidal osteoma carries important clinical implications due to its predilection for the juxtapapillary and macular regions, where even small lesions may result in significant visual morbidity. The condition is often diagnosed incidentally during funduscopic examination or retinal imaging, but progressive visual impairment can occur over time, particularly when complications such as choroidal neovascularisation develop (1).
Epidemiology and risk factors
Choroidal osteoma typically presents in young adults, most commonly during their early twenties, with a marked female predominance (2). The tumour is usually unilateral although bilateral involvement has been reported in a minority of cases (3). The aetiology remains unclear and no definitive systemic risk factors have been identified. Unlike many other choroidal tumours, choroidal osteoma is not associated with known genetic syndromes or inflammatory conditions. Some hypotheses suggest a developmental, inflammatory, or reactive origin, but these remain speculative (2).
Pathophysiology
The defining feature of choroidal osteoma is the presence of mature cancellous bone within the choroid, replacing normal choroidal tissue. Histologically, the lesion consists of trabecular bone with marrow spaces, often containing vascular channels (4). Over time, lesions may undergo decalcification, a process that is strongly associated with photoreceptor loss and deterioration of visual acuity. Decalcification results in thinning of the overlying retinal pigment epithelium and outer retinal layers contributing to irreversible visual dysfunction. Secondary changes such as choroidal neovascularisations can arise from disruption of the Bruch’s membrane and chronic retinal pigment epithelial stress (5).
Clinical presentation
Many patients with choroidal osteoma are asymptomatic at presentation, particularly when lesions are small or located away from the fovea. When symptoms occur, they most commonly include gradual reduction in central vision, metamorphopsia, or scotoma (6). On fundoscopic examination, choroidal osteoma typically appears as a well demarcated yellow-orange or yellow-white lesion at the posterior pole, often adjacent to the optic disc. The lesion may demonstrate areas of variable pigmentation corresponding to calcified and decalcified regions. Overlying retinal pigment epithelial changes, including depigmentation or atrophy are common. Visual prognosis depends largely on lesion location, size and progression with macular involvement conferring a poorer outcome.
Diagnosis
Diagnosis of choroidal osteoma relies heavily on multimodal retinal imaging which provides characteristic findings that are often pathognomonic. Fundus photography reveals a well-defined, pale lesion with geographic borders. B-scan ultrasonography demonstrates a highly reflective choroidal mass with posterior acoustic shadowing reflecting its calcified nature. Optical coherence tomography (OCT) shows elevation of the choroid with disruption of the outer retinal layers and retinal pigment epithelium, particularly in areas of decalcification. Fundus autofluorescence highlights retinal pigment epithelial stress and atrophy. Finally, CT scans can confirm calcification and maybe useful when diagnostic uncertainty exists (7,8).
Management
There is currently no definitive treatment for choroidal osteoma itself. Management is largely conservative and focused on monitoring and treating complications. Observation is appropriate for asymptomatic patients with stable lesions. Regular follow-up with visual acuity testing and retinal imaging is essential to detect progression or secondary pathology. Choroidal neovascularisations, the most common vision threatening complication is managed with intravitreal anti-vascular endothelial growth factor (anti-VEGF) therapy (9). These agents have demonstrated efficacy in stabilising or improving vision in affected patients. Other treatment modalities including photodynamic therapy and laser photocoagulation have been explored historically but are generally avoided due to the risk of exacerbating retinal damage and accelerating decalcification. Patient counselling is crucial, as visual decline may be gradual and unpredictable. Early recognition of new symptoms allows prompt intervention for treatable complications (10).
Prognosis
The long-term prognosis of choroidal osteoma is variable. While many lesions remain stable over years, progressive decalcification and macular involvement are associated with significant visual loss. Studies suggest that a substantial proportion of patients experience moderate to severe visual impairment over a long-term follow-up. Regular surveillance with OCT and fundus imaging allows clinicians to monitor structural changes and intervene early when complications arise. Given the chronic nature of the condition, long-term follow-up is recommended even in asymptomatic individuals (11).
Conclusion
Choroidal osteoma is a rare, benign choroidal tumour with potentially significant visual consequences. Advances in retinal imaging have improved diagnostic confidence and understanding of disease progression. While no curative treatment exists, vigilant monitoring and timely management of complications, particularly choroidal neovascularisation, can preserve vision and improve quality of life.
References
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