Sir,

A 25-year-old Sri Lankan man presented with gradual deteriorating vision uncorrectable with spectacles. His best spectacle corrected visual acuity was 6/18 (right) and 6/9 (left), with no improvement with pinhole. Anterior segment examination showed Vogt’s striae in both corneas. Fundoscopy revealed bilateral astrocytic hamartomas on the disc and nasal retinal hamartoma in the right (Figure 1b). Further examination revealed adenoma sebaceum (Figure 1a) and shagreen patch (Figure 1c).

Figure 1
figure 1

Corneal topography (Orbscan).

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Corneal topography (Figure 2) showed corneal changes characteristic of keratoconus with inferior steepening on the right (Figure 2a) and relatively unaffected left eye (Figure 2b).

Figure 2
figure 2

(a) Fundus photograph (hamartoma). (b) Adenoma sebaceum. (c) Shagreen patch.

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He is fit and well with no epilepsy, mental illness, renal disease, or atopy. He has no risk factors of keratoconus such as steroid use or vernal conjunctivitis. There is no family history of tuberous sclerosis or keratoconus.

This patient was referred for gas-permeable contact lens.

Tuberous sclerosis or Bourneville’s disease is a phakomatoses that can be autosomal dominant or sporadic. Typical ocular findings include retinal and optic nerve astrocytic hamartomas.1 Less commonly reported associations include cataracts,2 premacular gliosis,3 and iridociliary hamartomas.4 To the best of our knowledge, the association to keratoconus has never been published.

Tuberous sclerosis is caused by mutations in 9q34 (TSC1) and 16p13 (TSC2), which code for tumour suppressors hamartin and tuberin, respectively. Therefore, their association with hamartomas and various neoplasms5 is not surprising. However, an association to an ecstatic corneal pathology is difficult to explain.

The pathogenesis of keratoconus is genetically heterogeneous and most commonly sporadic, but various genetic loci have been identified including 5q14.3–q21.1,6 3p14–q13,7 and 16q22.3–q23.1.8 It is difficult to explain the link on genetic terms as no loci for keratoconus have been found near TSC1 or TSC2. Unlike PKD1 (polycystic kidney disease), which lies adjacent to TSC2 at 16p13.3, the loci for keratoconus have been located on chromosomes 5, 3, and 16q. However, studies have shown HLA-A28 to be associated with both tuberous sclerosis9 and keratoconus.10 Perhaps, there are genetic linkages between the two diseases but, as there was no family history of either tuberous sclerosis or keratoconus, it may be coincidental as both are known to occur sporadically.

We did not feel HLA typing was indicated in this patient, as it would not have changed the management of this patient. Furthermore, knowledge of HLA typing would not have enabled us to advise this patient regarding the likelihood of his children developing keratoconus. Therefore, as we still know very little regarding the linkage of the two diseases, the management of this patient included treating the keratoconus and genetic counselling for tuberous sclerosis. Further genetic studies may provide further proof and aid in management of these patients.