Focal Scleral Nodule
Focal scleral nodules were first described in 1996 with the name unifocal helioid choroiditis. Later, similar lesions were described using the name solitary idiopathic choroiditis. Finally, with the advent of optical coherence tomography, enabling further investigation of these lesions, it was discovered that they in fact originated from the sclera, and thus leading to our current nomenclature of focal scleral nodule.
These benign lesions are characteristically yellow or white, elevated, round and postequatorial. Their appearance may be concerning for choroidal melanoma or metastasis but can be distinguished from those lesions by careful clinical exam and optical coherence tomography. They are rarely visually significant and usually do not require any intervention.
A focal scleral nodule (FSN) is a yellow-white, elevated, round, non neoplastic lesion arising from the sclera and classically located posterior to the equator.
FSN was first described by Hong et al in 1996 and was termed unifocal helioid choroiditis.  Later, Shields et al published a study of 60 lesions and termed the condition solitary idiopathic choroiditis. With the development and use of OCT, these lesions were further investigated and found to have a scleral origin. In 2020, Fung et al published a retrospective observational study further investigating these nodules and coined the term focal scleral nodule due to the absence of choroiditis and its origin in the sclera.
To date there is limited data on the prevalence of FSN. Studies have shown a wide range of presenting ages with patients as young as three and as old as eighty-three. There is some evidence that it may be more common in females and Caucasians. 
Risk factors remain poorly understood likely due to the poor understanding of the pathogenesis. Several associations have been suggested including associations with systemic diseases such tuberculosis, syphilis, sarcoidosis, cat scratch disease and coxsackie virus.  However, this remains unclear and has been challenged in recent literature; no significant relation with these systemic conditions has been found.
The pathology of FSN lesions is poorly understood and will require future investigation. One theory is that it may be a congenital condition that may develop prior to birth as evidenced by its occurrence in some young individuals.
Diagnosis is made clinically based on physical examination and imaging.
FSN classically presents as a yellow or yellow-white elevated lesion. It is frequently accompanied by an associated orange halo surrounding the lesion. Retinal pigment epithelial changes are variable and may demonstrate atrophy. Nearly all lesions will be postequatorial and are most commonly noted near the optic nerve. They have been shown to generally have a size of approximately one disk diameter. The majority of the lesions are inactive and have well defined boarders. However, some lesions may appear active with associated inflammation and poorly defined boarders. Feng et al reported an active lesion yellowish lesion with ill-defined margins with subretinal fluid and focal retinal hemorrhages that became quiescent without treatment within 6 weeks into a yellow inactive dry FSN lesion with an orange halo .
Optical coherence tomography (OCT) has led to new understanding of FSN including the anatomic origin in the sclera vs the choroid as previously described. Most lesions have been revealed to have a dome shape, but nodular or volcanic shape have also been noted. Overlying choroid usually shows thinning or absence and is the likely cause of the orange halo seen on fundoscopic exam. OCT angiography will show the lesions to be avascular and most will demonstrate hyperautofluorescence.
Signs and Symptoms
Effects on vision are variable with the majority being asymptomatic. In patients with symptoms, the most common were floaters or blurry vision in the affected eye. Some of the visual complaints may also be related to the lesion’s relationship to the macula as it may induce abnormal architecture in the macula and fovea.
Many lesions have a somewhat similar presentation to FSN. Some of which are benign while others are may indicate a more urgent or dangerous disease. A thorough exam and imaging are important to differentiate these lesions and many can be ruled out with OCT showing a scleral lesion vs a lesion arising from the choroid. 
The following lesions may present similarly:
- Choroidal metastasis
- Choroidal melanoma
- Choroidal lymphoma
- Astrocytic hamartoma
- Choroidal nevus
- Choroidal granuloma
- Choroidal scars
- White dot syndromes
- Ocular tuberculosis
- Ocular syphilis
- Fungal chorioretinitis
- Sclerchoroidal calcification
Of note, a FSN may easily be mistaken for sclerochoroidal calcification which also arises from the sclera as shown on OCT. Furthermore, it may present with similar thinning of the overlying choroid. However, sclerochoroidal calcifications are often more peripheral compared to FSN lesions. They also demonstrate more irregular shapes compared to the characteristically round FSN lesion and are often association with systemic conditions related to calcium metabolism.  Bscan will reveal hyperintensity in the area of sclerochoroidal calcification.
When followed over time most FSN lesions remain stable without changes. Nevertheless, there are reports of lesions that demonstrate growth or resolution with long-term follow-up.
When followed over time most lesions remain stable without changes. Nevertheless, there are reports of lesions that demonstrate growth or resolution with long-term follow-up. 
Due to the benign nature and limited functional impact of a FSN, no treatment is indicated in most cases. In the event that a lesion does appear to be active with associated inflammation, systemic steroids have been suggested as a possible trial treatment.  However, there have been no studies evaluating the overall effectiveness of this treatment. Active lesions can respond favorable with or without steroid treatment. 
Regardless, due to the potential danger similar-looking lesions it is imperative to correctly diagnose a FSN prior to informing a patient that they do not need follow-up care. The potential erroneous diagnosis of a FSN in place of a choroidal metastasis or melanoma could be disastrous.
- Hong PH, Jampol LM, Dodwell DG, Hrisomalos NF, Lyon AT. Unifocal helioid choroiditis. Arch Ophthalmol. 1997 Aug;115(8):1007-13.
- Shields JA, Shields CL, Demirci H, Hanovar S. Solitary Idiopathic Choroiditis: The Richard B. Weaver Lecture. Arch Ophthalmol. 2002;120(3):311–319.
- Fung AT, Kaliki S, Shields CL, Mashayekhi A, Shields JA. Solitary idiopathic choroiditis: findings on enhanced depth imaging optical coherence tomography in 10 cases. Ophthalmology. 2013;120:852–858
- Fung AT, Waldstein SM, Gal-Or O, Pellegrini M, Preziosa C, Shields JA, Welch RJ, Dolz-Marco R, Sarraf D, Nagiel A, Lalane R, Jung JJ, Ghazi NG, Ramtohul P, Arnold JJ, Sakurada Y, Choudhry N, Balaratnasingam C, Freund KB, Shields CL. Focal Scleral Nodule: A New Name for Solitary Idiopathic Choroiditis and Unifocal Helioid Choroiditis. Ophthalmology. 2020 Nov;127(11):1567-1577.
- Goyal S, Ware GT, Petrovic' V. Coxsackie virus a possible missing link to unifocal helioid choroiditis? Clin Exp Ophthalmol. 2015 May-Jun;43(4):377-9.
- Kumar V, Khoo CT, Shields CL. Solitary idiopathic choroiditis in the setting of extensive animal exposure. Retin Cases Brief Rep. 2016 Fall;10(4):386-8.
- Feng Y, Conrady CD, Demirci H. The evolution of an active solitary idiopathic choroiditis (focal scleral nodule): a case report of the natural course and a review of the literature. BMC Ophthalmol. 2021;21(1):130. Published 2021 Mar 9. doi:10.1186/s12886-021-01888-5