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Macular corneal dystrophy: for professionals


Clinical phenotype

Incidence
  • Unknown
  • Most common autosomal recessive corneal dystrophy in Middle East, South Asia and Iceland[1]
Corneal Features
  • Diffuse stromal haze initially
  • Followed by central, sharply defined spots (stromal flecks) located at the pre-Descemet stroma, extending to the limbus over time
  • “Large snowflakes and fog” appearance
  • Abnormally thin cornea is characteristic
Symptoms
  • Disease onset: first decade of life
  • Variable severity
  • Some are asymptomatic
  • Most experience photophobia, glare and reduced VA
  • Painful erosions are uncommon
There is a ring of white opaque deposits at the periphery of the cornea, at the border with the white of the eye. The central cornea is also hazy.
A ring of deep pre-Descemet stromal opacities in the peripheral cornea. The central cornea is hazy with a reduced stromal thickness.

Credit: Mr Stephen Tuft, consultant ophthalmologist, Moorfields Eye Hospital, London

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Genetics

Gene (OMIM no.) and associated function
  • CHST6 (#217800)
  • Encodes corneal N-acetylglucosamine-6-sulfotransferase
  • Inactivation of the CHST6 protein causes accumulation of acid mucopolysaccharides in keratocytes and cytoplasm of endothelial cells[2]
  • Secondary endothelial decompensation is rare
Inheritance pattern

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Key investigations

Macular corneal dystrophy (MCD) has been subclassified into three immunophenotypes (MCD1, MCD1A and MCD2) based on the presence or absence of keratin sulphate antigen in serum and cornea. Routine measurement of keratin sulphate is not required as the subtypes are clinically indistinguishable and are all caused by biallelic CHST6 mutations.[3]

Thinning of the central cornea can be observed with Scheimpflug imaging (Pentacam)[4] or anterior segment OCT.

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Diagnosis

MCD can be diagnosed clinically. Genetic testing can be undertaken to confirm the diagnosis, facilitate genetic counselling, provide accurate advice on prognosis and future family planning, and aid in clinical trial participation.

This can be achieved through a variety of next generation sequencing (NGS) methods:

  • Targeted gene panels (anterior segment dysgenesis)
  • Whole exome sequencing
  • Whole genome sequencing

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Management

  • Glasses or contact lenses to correct refractive errors
  • Topical lubricants and/or extended wear therapeutic contact lenses are primary therapeutic options for recurrent corneal erosions; topical antibiotics can be added to prevent secondary infections
  • Surgical interventions to remove opacity— Deep anterior lamellar keratoplasty (DALK) are associated with less post-operative complications such as endothelial cell loss and secondary glaucoma compared to penetrating keratoplasties but recurrence rates are higher with DALKs at 5 years[5,6] 
  • Excimer laser superficial phototherapeutic keratectomy (PTK) can be considered in patients with repeated corneal erosions to delay the need for keratoplasties[1]

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Further information and support

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References

  1.  Aggarwal S, Peck T, Golen J, Karcioglu ZA. Macular corneal dystrophy: A review. Surv Ophthalmol. Sep – Oct 2018;63(5):609-617. doi:10.1016/j.survophthal.2018.03.004
  2.  Akama TO, Nishida K, Nakayama J, et al. Macular corneal dystrophy type I and type II are caused by distinct mutations in a new sulphotransferase gene. Nat Genet. Oct 2000;26(2):237-41. doi:10.1038/79987
  3.  Jonasson F, Oshima E, Thonar EJ, Smith CF, Johannsson JH, Klintworth GK. Macular corneal dystrophy in Iceland. A clinical, genealogic, and immunohistochemical study of 28 patients. Ophthalmology. Jul 1996;103(7):1111-7. doi:10.1016/s0161-6420(96)30559-9
  4.  Kocluk Y, Yalniz-Akkaya Z, Burcu A, Ornek F. Corneal topography analysis of stromal corneal dystrophies. Pak J Med Sci. Jan-Feb 2015;31(1):116-20. doi:10.12669/pjms.311.6292
  5.  Reddy JC, Murthy SI, Vaddavalli PK, et al. Clinical outcomes and risk factors for graft failure after deep anterior lamellar keratoplasty and penetrating keratoplasty for macular corneal dystrophy. Cornea. Feb 2015;34(2):171-6. doi:10.1097/ico.0000000000000327
  6.  Cheng J, Qi X, Zhao J, Zhai H, Xie L. Comparison of penetrating keratoplasty and deep lamellar keratoplasty for macular corneal dystrophy and risk factors of recurrence. Ophthalmology. Jan 2013;120(1):34-9. doi:10.1016/j.ophtha.2012.07.037

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Updated on November 30, 2020
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