Ophthalmic Manifestations of Tuberous Sclerosis
Tuberous sclerosis complex (TSC) is a genetic disorder characterized by autosomal dominant mutation of tumor suppressor genes TSC1 and TSC2 with near complete dominance. TSC1 and TSC2 gene products, hamartin and tuberin respectively, control cellular growth and proliferation by forming a complex that inhibits the mechanistic target of rapamycin (mTOR), a key regulator in the pathway of cellular proliferation. A loss of function mutation in either TSC1 or TSC2 results in uninhibited cell cycle progression and the consequential development of systemic hamartomas, or circumscribed, benign and non-invasive tumors located within a given organ and comprised of disorganized cells with dysplastic cytoarchitecture.
The most common presentation of this disease is characterized by benign tumors affecting the neurologic, dermatologic, renal, cardiac, pulmonary and ocular systems, and the most classic triad of symptoms is described as seizures, mental disability, and cutaneous angiofibromas. However, this complete triad is only present in 29% of patients, and 6% of TSC patients lack all three of the clinical manifestations. Due to the highly variable expressivity of this disease, the same genotype can produce a wide array of clinical signs and the specific clinical manifestations of a given patient can change throughout their life. The ophthalmic presentations of TSC are typically non-progressive astrocytic retinal hamartomas, but hamartomas of the optic nerve, iris, and ciliary epithelium have been described in association with TSC as well.
The incidence of TSC is thought to range between 1/5,000-1/10,000 live births, with women and men affected equally across all ethnic groups. There are approximately 20,000 recorded affected individuals worldwide. With respect to the presence of retinal hamartomas, these benign lesions have been described in approximately 30-50% of TSC patients. However, the presence of retinal hamartomas is not necessarily pathognomonic for TSC since there are reports of similar lesions as isolated lesions or in patients with neurofibromatosis or retinitis pigmentosa patients. While the specific prevalence of retinal hamartomas has not been described in non-TSC populations, various case reports and one case series of 3,573 healthy newborns have estimated that the prevalence of retinal hamartomas in non-TSC populations is very rare, as only two infants in the case series presented with these benign lesions.
Tuberous sclerosis is most frequently characterized by loss of function mutations in tuberous sclerosis-1 (TSC1) or tuberous sclerosis-2 (TSC2) genes located on chromosomes 9 and 16, respectively. Tuberous sclerosis caused by TSC1 is due to a heterozygous mutation of the TSC1 gene located on chromosome 9q34, which codes for hamartin protein. Tuberous sclerosis caused by TSC2 is due to a heterozygous mutation of the TSC2 gene located on chromosome 16p13.23, which codes for tuberin protein.
The TSC complex is characterized by the interaction between TSC1 and TSC2 gene products hamartin and tuberin. The most commonly described mechanism of action of these two gene products involves hamartin functioning to stabilize tuberin, while tuberin acts as a GTPase-activating protein for guanosine triphosphate hydrolase (GTPase) Ras homolog enriched in brain (Rheb). A loss of function mutation in either TSC1 or TSC2 leads to increased Rheb-GTP levels and downstream activation of mTOR complex 1 (mTORC1). This activation induces a downstream kinase pathway, leading to the phosphorylation of p70 S6 kinase and eukaryotic translation initiation factor 4E-binding protein (4E-BP1). Increased mTOR activity causes uninhibited cellular overgrowth and the consequential development of tumors, most frequently described as hamartomas. The continual activation of mTOR also leads to an increase in vascular endothelial growth factor (VEGF) which further facilitates tumor growth.
TSC2 mutations occur in 75-80% of patients, making this version of the disease more common than TSC1 mutations, which occur in 10-30% of patients. This disease demonstrates near complete penetrance in affected patient populations, and a disease-causing mutation of either TSC1 or TSC2 can be identified in up to 90% of cases. About 60% of cases are caused by sporadic mutations, and 40% of cases are inherited in a familial autosomal dominant pattern.
Although TSC has near complete penetrance, there is also variable expressivity presumed due to the Knudson “two hit hypothesis”. The first hit is the pre-existing mutation of either TSC1 or TSC2, and the second mutation within the same gene induces a loss of heterozygosity. TSC2 mutations are known to produce a more severe phenotype than TSC1 mutations and are also correlated with more significant retinal findings. Patients with retinal findings are further correlated with other severe TSC complications, such as epilepsy, renal angiomyolipoma, subependymal giant cell astrocytomas (SEGAs), and significant cognitive impairment. The development of retinal hamartomas is due to the unregulated growth of glial astrocytes and associated blood vessels.
Retinal astrocytic hamartomas are characterized by a network of glial astrocytes and blood vessels, with lesions developing most frequently in the nerve fiber layer near or at the posterior pole. Basophilic hyaline and calcium deposits may be detected in these lesions as well.
The clinical diagnosis of TSC involves genetic testing and physical examination findings. Funduscopic examination of the anterior and posterior segments is a critical component of the diagnosis and management of TSC, and may be used in conjunction with other diagnostic measures to follow the progression of ocular hamartomas.
The diagnostic criteria for TSC was established and most recently updated by the International Tuberous Sclerosis Complex Consensus Group in 2012. A probable TSC diagnosis requires either 1) identification of a TSC1 and/or TSC2 pathogenic mutation via genetic testing or 2) two major and one minor feature from a list of TSC diagnostic criteria, as listed in the table below.
|Major Features||Minor Features|
|Hypomelanotic macules (≥3, at least 5-mm diameter)||“Confetti” skin lesions|
|Angiofibromas (≥3) or fibrous cephalic plaque||Dental enamel pits (>3)|
|Ungual fibromas (≥2)||Intraoral fibromas (≥2)|
|Shagreen patch||Retinal achromic patch|
|Multiple retinal hamartomas||Multiple renal cysts|
|Cortical dysplasias||Nonrenal hamartomas|
|Subependymal giant cell astrocytoma|
|Definite diagnosis: Two major features or one major feature with ≥2 minor features|
|Possible diagnosis: Either one major feature or ≥2 minor features|
With respect to genetic testing, it is important to note that a significant fraction (10-25%) of TSC patients have no mutation identified by conventional genetic analysis; as such, the clinical criteria have a significant role in appropriate diagnosis.
I. Retinal Findings
Retinal hamartomas are the only ocular manifestation of TSC used as a major feature used for diagnosis and are histologically characterized by fibrotic astrocytes with small oval nuclei and long cytoplasmic extensions. They are present in approximately 50% of TSC patients, with bilateral presentation in 25% of TSC patients. A related clinical presentation used as a minor feature for diagnosis are retinal achromatic patches, which are not clearly described but could represent a flat astrocytic hamartoma versus a description of an RPE depigmented lesion. There are three main types of benign, typically non-progressive retinal hamartomas described in TSC patients, as well an additional aggressive type described in a few case reports.
a. Flat Hamartomas: Flat hamartomas are the most common type found in TSC patients and represent a “young tuberous body”.  These lesions are characterized by light grey or yellow coloration and translucent with distinct borders. Flat hamartomas lack calcifications and can be difficult to identify on examination due to their translucency. Their frequent location towards the temporal ends of vascular arcades and consequential obscuration of the vessels can help in identification. These obscured vessels are often frail and are prone to causing vitreous hemorrhages.
b. Multinodular Hamartomas: Multinodular hamartomas are the second most common type of retinal lesion in TSC patients and are typically described as a “mulberry” or “fish egg” lesion with calcifications. These “older tuberous bodies” are frequently in the posterior pole as well as peripapillary and epi-papillary locations; consequently, they can be mistaken for optic disc drusen. Their typical size ranges between one-half and four-disc diameters. These calcifications can be demonstrated on orbital B-scan ultrasonography as hyperechogenic with posterior shadowing and are typically associated with high acoustic density.
c. Transitional Hamartomas: Transitional hamartomas are less common, occurring in only 9-12% of TSC patients. They are characterized by a combination of features of flat and multinodular astrocytic hamartomas. The base of the lesion may appear flat and translucent with a centrally nodular, calcified appearance.
d. Aggressive Hamartomas: Although most retinal hamartomas are considered to be benign and stationary, there have been case reports of aggressive hamartomas that demonstrate progressive growth and can threaten vision. Shields et al. reported four TSC patients with peripapillary retinal neoplasms that demonstrated growth. Neovascular glaucoma and exudative retinal detachment developed secondarily to tumor expansion. These tumors were treated with surgery and laser therapy in two of the cases, but in all four cases, enucleation was eventually required due to a blind, painful eye. Another case study of a TSC patient with an aggressive variant of retinal hamartoma presented with macular edema and neovascularization, which was treated successfully with a single intravitreal injection of 1.25 mg bevacizumab. However, these progressive-type lesions are very rare in patients with tuberous sclerosis.
II. Neuro-Ophthalmological Findings
a. Optic Nerve Hamartomas: Astrocytic hamartomas can affect the optic nerve directly but are generally benign and do not require treatment. These lesions, when on the surface of the optic nerve, are characterized by an elevated optic nerve head with the appearance of obscured borders. As such, optic nerve hamartomas can imitate the appearance of optic nerve edema and require close inspection for differentiation. These lesions are typically unilateral and can also contain calcified regions, which may resemble optic disc drusen on examination. Astrocytic hamartomas involving the optic nerve head are typically asymptomatic and non-progressive, unlike true papilledema which is characterized by elevated intracranial pressure with secondary nausea/vomiting, transient visual obscuration, and pulsatile tinnitus.
b. Papilledema: Obstructive hydrocephalus can cause papilledema secondary to Subependymal Giant Cell Astrocytomas (SEGAs). SEGA are present in approximately 20% of TSC patients and are considered a major feature used for diagnosis. SEGA are typically histologically benign and slow growing, but with sufficient growth can black the foramen of Monro where they are frequently located, consequently obstructing the drainage of cerebral spinal fluid and causing obstructive hydrocephalus. This complication will typically present with bilateral papilledema and induce symptoms of worsening headaches with nausea, vomiting, elevated ICP, transient visual obscuration, and pulsatile tinnitus. Obstructive hydrocephalus caused by proliferating SEGA can be associated with a full or partial cranial nerve VI palsy. Observed papilledema in a TSC patient would necessitate urgent neurological imaging with computed tomography or magnetic resonance imaging for assessment of potential obstructive hydrocephalus.
c. Cranial Nerve Palsies: Cranial nerve palsies are rare in TSC patients but could represent vision-threatening or even life-threatening pathology, such as obstructive hydrocephalus secondary to SEGA or an intracranial aneurysm. Both partial and complete palsies have been documented in association with TSC. The most commonly reported cranial nerve palsies is cranial nerve VI which is typically due to elevated intracranial pressure and presents clinically as an adducted eye with partial or complete inability to abduct. Cranial nerve III has also been reported in both pediatric and adult TSC patients and presents with ipsilateral ptosis, mydriasis and an abducted eye. Third nerve palsies are concerning for direct nerve compression by an enlarging, un-ruptured posterior communicating aneurysm. Ruptured aneurysms rarely manifest as a third-nerve palsy and present with severe neurologic symptoms, such as nausea/vomiting, neck stiffness, severe headache, and seizures. This potential underlying pathology in a TSC patient with third nerve palsy has a high mortality rate and should be treated emergently.
d. Cortical Visual Impairment: Cortical Visual Impairment (CVI) is a broad term used to describe all types of visual dysfunction caused by damage to the retro-chiasmal visual pathway and cerebral structures. CVI has a highly-variables presentation in TSC patients but is typically described as abnormally decreased vision for respective patient age group and fluctuating visual function. The lower hemi-field of vision is most commonly impaired in TSC patients experiencing CVI, although there is no evidence that this association is specific to TSC. Since approximately 90% of TSC patient have epilepsy, cortical brain malformations, and/or neuropsychiatric disorders, these manifestations imply some degree of neurological dysfunction, which is highly correlated with CVI. Due to the high level of neurological dysfunction and correlation with visual function, it is likely that most patients with TSC have some degree of CVI. This is often difficult to ascertain, however, due to lack of cooperation with testing since many TSC patients have moderate to severe intellectual disability. CVI has a highly variable prognosis.
e. Visual Field Defects: Visual field defects in tuberous sclerosis patients have a variety of different etiologies, including astrocytic hamartomas, obstructive hydrocephalus from SEGA, CVI, or as a side effect of anti-epileptic drugs (e.g., vigabatrin). Large astrocytic hamartomas of the retina are typically asymptomatic but can occasionally cause arcuate visual field defects corresponding to the location of the hamartoma. However, due to the significant functional overlap between visual fields in binocular patients and the typically small size of defect, astrocytic hamartomas rarely are visually significant. Hamartomas that are intrinsic to the optic nerve have a greater risk of causing visual field defects as these lesions are known to occasionally enlarge and induce progressive vision loss. CVI-related visual field defects most commonly affect the lower hemi-field of vision, but this association has not been proven to be specific to TSC patients. Vigabatrin is an anti-epileptic medication used to treat infantile spasms in children with TSC and in some adult patients with partial spasms and has been shown to cause constriction of peripheral visual fields due to toxic systemic side effects in 52% of adult TSC patients and 34% of pediatric patients. However, in a subsequent study performed by the Risk Evaluation and Mitigation Strategies (REMS), preexisting baseline visual deficits accounted for up to 37% of vision loss in vigabatrin-treated TSC patients, with only 2% of patients demonstrating new visual defects after vigabatrin use. This study indicates that concentric peripheral vision field loss in vigabatrin-treated TSC patients may be due more to pre-existing visual limitations than previously believed.
III. Anterior Segment Findings
Palpebral angiofibromas are one of the most common ophthalmological manifestations of tuberous sclerosis and are characterized by eyelid neoplasms in both pediatric and adult TSC patient populations. Hypopigmented sectoral lesions and hamartomas of the iris and ciliary body have been also documented in TSC patients. Other recorded anterior segment findings include strabismus, poliosis of the eyelashes, and coloboma of the iris, lens, and choroid. Atypical colobomas, or ocular colobomas outside the inferonasal quadrant, are associated with TSC and may be secondary to iris hamartomas of the iris pigment epithelium and ciliary epithelium.
IV. Other Pertinent Findings
Other associated ocular findings in TSC patients include increased association with myopia and astigmatism and decreased associated with hyperopia.
Retinal hamartomas can be evaluated using fundus photography to assess growth progression and optical coherence tomography to assess thickness or associated fluid, if suspected. Optic nerve hamartomas can similarly be evaluated with fundus photography and optical coherence tomography, but additionally may warrant formal visual field testing if progressive vision loss is suspected. Additionally, formal visual field testing, assessment of relative afferent pupillary defect, neurological imaging and/or lumbar puncture are useful in discriminating optic nerve hamartomas from papilledema secondary to SEGA-induced obstructive hydrocephalus.
Genetic testing plays a critical role in the diagnosis of tuberous sclerosis, as the identification of a TSC1 or TSC2 pathogenic mutation, or a mutation that inactivates the function of the gene product, from regular tissue is sufficient to make a conclusive diagnosis. Genetic testing further aids in estimating a patient’s prognosis since TSC2 mutations are associated with more severe systemic effects than TSC1 mutations. However, due to the highly variable presentation of the disease, the predictive power of genetic testing is limited and cannot be solely used in assessing a the prognosis of TSC. Furthermore, 10-25% of symptomatic TSC patients lack a TSC1/2 mutation detected by conventional genetic analysis, which additionally indicates the restricted power of genetic testing in making a diagnosis of TSC.
Due to overlapping presentation of tuberous sclerosis complex with other phakomatoses and systemic disorders, it is important to consider the differential diagnoses of ocular hamartomas. The differential diagnoses relevant to retinal astrocytic hamartomas include retinoblastoma, retinitis pigmentosa, and neurofibromatosis. Genetic testing and systemic diagnostic evaluation using major and minor criteria can help aid in diagnosis of TSC.
The differential diagnoses relevant to optic nerve-involving hamartomas involve optic nerve edema and optic disc drusen, if the hamartoma is calcified. Optic nerve edema typically implies either papilledema or inflammation, infiltration or compression of the optic nerve. Both true optic nerve edema and optic nerve hamartomas are characterized by blurred nerve borders. As such, a thorough history and full neurological workup including neurological imaging of the brain and orbits with potential lumbar puncture is warranted to rule out obstructive hydrocephaly or other vision/life-threatening disorders. A calcified hamartoma can closely resemble optic disc drusen, which are acellular deposits in the optic nerve that become progressively more superficial with increased age. Optic disc drusen is found is approximately 2% of the population and may have effects on visual fields; however, more frequently, both disc drusen and hamartomas are asymptomatic and have similar managements including regular dilated fundus examinations, fundus photography, and visual field testing.
Ophthalmic Screening for TSC: Patients with TSC should undergo annual evaluation with a dilated fundus examination to ensure that size progression and/or development of fluid associated with the lesions has not occurred. Exudative detachments secondary to hamartomas have been reported in case reports, but are incredibly rare. Both retinal and optic nerve hamartomas can further be assessed using fundus photography and optical coherence tomography to document progression. If vision loss is suspected, formal visual field testing may be indicated to assess for progressive loss in visual function or secondary pathologies, such as papilledema. For TSC patients taking vigabatrin for infantile spasms, potential accumulative drug toxicity may be considered and evaluated with formal visual field testing if peripheral visual field loss is suspected. Electroretinography (ERG) may be used in patients as a tool to monitor decreases in visual potential in TSC infants and intellectually disabled adults who cannot reliably undergo formal visual field testing.
Systemic Medical Therapy: Potential therapies used for TSC include sirolimus, a mTOR inhibitor, and interferon-gamma. Everolimus, a different mTOR inhibitor, can be combined with sirolimus to treat intractable epilepsy in TSC. Zipori et al. suggested that everolimus could potentially reduce the number and size of retinal hamartomas. Furthermore, vigabatrin is an effective medication approved by the FDA for treatment of infantile spasms, but systemic toxicity due to accumulation of the drug has been demonstrated.
Ophthalmic medical therapy
Retinal and optic nerve hamartomas rarely require treatment, as they are typically non-progressive and asymptomatic. However, various medical treatment options have been rarely used to treat symptomatic retinal hamartomas and their sequelae.
I. Intravitreal bevacizumab: Several case reports of intraretinal hemorrhage and macular edema secondary to hamartoma progression have been shown to respond to intravitreal bevacizumab or combined bevacizumab with triamcinolone.
II. Laser Therapy: The development and persistence of subretinal fluid secondary to aggressive-type retinal hamartomas has been shown to respond to argon laser photocoagulation, which induces fluid reabsorption. However, recurrent treatment has been associated with choroidal neovascularization. Photodynamic therapy has instead been suggested as an effective alternative for aggressive retinal astrocytomas with fewer side effects.
Surgery is very rarely indicated and has typically only been performed for non-clearing vitreous hemorrhage secondary to retinal astrocytomas progression. However, aggressive lesions have been shown to generally not respond well to pars plana vitrectomy (PPV) procedures. Case reports of aggressive astrocytomas have required enucleation as surgical intervention for a blind, painful eye. However, one case report by Nakayama et al. in 2012 demonstrated a TSC patient who developed an exudative detachment and retinal neovascularization secondary to an aggressive retinal astrocytic hamartoma and responded positively to PPV and intravitreal bevacizumab.
Retinal hamartomas in TSC patients are generally stable over time and very rarely have deleterious visual effects. As such, these lesions generally do not require any medical or surgical intervention. A longitudinal study performed by Zimmer-Galler et al. suggests that while flat retinal hamartomas typically remain stable in size, they may become calcified over time and, less frequently, can enlarge. Hamartomas on the surface of the optic nerve are also commonly asymptomatic and have no effect on visual function in TSC patients.
- Hodgson, N., Kinori, M., Goldbaum, M. H., & Robbins, S. L. (2016). Ophthalmic manifestations of tuberous sclerosis: A review. Clinical & Experimental Ophthalmology, 45(1), 81-86.
- Schwartz, R. A., Fernández, G., Kotulska, K., & Jóźwiak, S. (2007). Tuberous sclerosis complex: Advances in diagnosis, genetics, and management. Journal of the American Academy of Dermatology, 57(2), 189–202.
- Borkowska, J., Schwartz, R. A., Kotulska, K., & Jozwiak, S. (2010). Tuberous sclerosis complex: tumors and tumorigenesis. International Journal of Dermatology, 50(1), 13–20.
- Wan, M., Chan, K. L., Jastrzembski, B. G., & Ali, A. (2019). Neuro-ophthalmological manifestations of tuberous sclerosis: current perspectives. Eye and Brain, Volume 11, 13–23.
- Zimmer-Galler, I. E., & Robertson, D. M. (1995). Long-term Observation of Retinal Lesions in Tuberous Sclerosis. American Journal of Ophthalmology, 119(3), 318–324.
- Eagle, R. C., Shields, J., & Shields, C. L. (2000). Hamartomas of the Iris and Ciliary Epithelium in Tuberous Sclerosis Complex. Archives of Ophthalmology, 118(5), 711.
- Northrup, H., & Krueger, D. A. (2013). Tuberous Sclerosis Complex Diagnostic Criteria Update: Recommendations of the 2012 International Tuberous Sclerosis Complex Consensus Conference. Pediatric Neurology, 49(4), 243-254.
- Shields, J. A., Eagle, R. A., Jr., Shields, C. L., & Marr, B. P. (2004). Aggressive Retinal Astrocytomas in Four Patients with Tuberous Sclerosis Complex. Transactions of the American Ophthalmological Society, 102, 139-148.
- Robertson, D. M. (1991). Ophthalmic manifestations of tuberous sclerosis. Annals of the New York Academy of Sciences, 615(1), 17-25.
- Rowley SA, O'Callaghan FJ, Osborne JP. (2001). Ophthalmic manifestations of tuberous sclerosis: a population based study. British Journal of Ophthalmology, 85, 420-423.
- Shields, C. L. (2012). Retinal Pigment Epithelial Depigmented Lesions Associated With Tuberous Sclerosis Complex. Archives of Ophthalmology, 130(3), 387.
- Abdolrahimzadeh, S., Plateroti, A. M., Recupero, S. M., & Lambiase, A. (2016). An Update on the Ophthalmologic Features in the Phakomatoses. Journal of Ophthalmology, 2016, 1–15.
- Rajasekaran, N. M., Horo, S., & Kuriakose, T. (2019). Primary ocular presentation of tuberous sclerosis – A case report. Indian Journal of Ophthalmology, 67(3), 433.
- Maguire, M. J., Hemming, K., Wild, J. M., Hutton, J. L., & Marson, A. G. (2010). Prevalence of visual field loss following exposure to vigabatrin therapy: a systematic review. Epilepsia, 51(12), 2423–2431.
- Foroozan R. (2018). Vigabatrin: Lessons Learned From the United States Experience. Journal of neuro-ophthalmology : the official journal of the North American Neuro-Ophthalmology Society, 38(4), 442–450.
- Lopez, J. P., Ossandón, D., Miller, P., Sánchez, L., & Winter, A. (2009). Unilateral eyelid angiofibroma with complete blepharoptosis as the presenting sign of tuberous sclerosis. Journal of American Association for Pediatric Ophthalmology and Strabismus, 13(4), 413–414.
- Mencía-Gutiérrez, E., Gutiérrez-Díaz, E., Ricoy, J. R., & Sánez-Madrazo, N. (2004). Lesiones palpebrales y cutáneas como única manifestación de esclerosis tuberosa [Eyelid and cutaneous lesions as the sole indicators of tuberous sclerosis]. Archivos de la Sociedad Espanola de Oftalmologia, 79(8), 401–404.
- Bacci, G. M., Polizzi, S., Mari, F., Conti, V., Caputo, R., & Guerrini, R. (2020). Atypical Ocular Coloboma in Tuberous Sclerosis-2. Journal of Neuro-Ophthalmology, Publish Ahead of Print, 1–3.
- Zipori, A. B., Tehrani, N. N., & Ali, A. (2018). Retinal astrocytoma regression in tuberous sclerosis patients treated with everolimus. Journal of American Association for Pediatric Ophthalmology and Strabismus, 22(1), 76–79.
- Saito,W., Kase, S., Ohgami, K., Mori, S., Ohno, S.. Intravitreal anti-vascular endothelial growth factor therapy with bevacizumab for tuberous sclerosis with macular oedema. Acta Ophthalmologica, 2010; 88: 377–80
- Bloom, SM., Mahl, CF. (1991). Photocoagulation for serous detachment of the macula secondary to retinal astrocytoma. Retina. 11, 416-422.
- Eskelin, S., Tommila, P., Palosaari, T., Kivelä, T. Photodynamic therapy with verteporfin to induce regression of aggressive retinal astrocytomas. Acta Ophthalmologica, 2008; 86: 794–9
- Nakayama, M., Keino, H., Hirakata, A., Okada, A. A., & Terado, Y. (2012). Exudative retinal astrocytic hamartoma diagnosed and treated with pars plana vitrectomy and intravitreal bevacizumab. Eye, 26(9), 1272–1273.