Sclerocornea and Cornea Plana Are Distinct Entities

Abstract

In their otherwise excellent review of anterior segment dysgenesis, “A Review of Anterior Segment Dysgeneses” (Surv Ophthalmol 51:213–31, 2006), Idrees et al confuse sclerocornea and cornea plana. Their statement that peripheral corneal opacities alone are suggestive of sclerocornea is incorrect, and their photograph labeled as sclerocornea (Figure 2E in the article) actually shows the classic phenotype of recessive cornea plana. Although these two entities are confused in the older literature, 1 Elliott J.H. Feman S.S. O'Day D.M. Garber M. Hereditary sclerocornea. Arch Ophthalmol. 1985; 103: 676-679 Crossref PubMed Scopus (44) Google Scholar , 2 Howard Ro Abrahams I.W. Sclerocornea. Am J Ophthalmol. 1971; 71: 1254-1258 Abstract Full Text PDF PubMed Scopus (29) Google Scholar recessive cornea plana and typical sclerocornea are now known to be different conditions with distinct phenotypes. 3 Khan A.O. Aldahmesh M. Al-Saif A. Meyer B. Pellucid marginal degeneration coexistent with cornea plana in one member of a family exhibiting a novel KERA mutation. Br J Ophthalmol. 2005; 89: 1538-1540 Crossref PubMed Scopus (16) Google Scholar , 4 Pellegata N.S. Dieguez-Lucena J.L. Joensuu T. et al. Mutations in KERA, encoding keratocan, cause cornea plana. Nature Genet. 2000; 25: 91-95 Crossref PubMed Scopus (121) Google Scholar , 5 Sigler-Villanueva A. Tahvanainen E. Lindh S. et al. Autosomal dominant cornea plana: clinical findings in a Cuban family and a review of the literature. Ophthalmic Genet. 1997; 18: 55-62 Crossref PubMed Scopus (11) Google Scholar , 6 Young R.D. Quantock A.J. Sotozono C. et al. Sulphation patterns of keratan sulphate proteoglycan in sclerocornea resemble cornea rather than sclera. Br J Ophthalmol. 2006; 90: 391-393 Crossref PubMed Scopus (8) Google Scholar Recessive cornea plana is bilateral and characterized by high hyperopia, small flat cornea, hazy corneal limbus, and variable incomplete opacity in the corneal parenchyma. 3 Khan A.O. Aldahmesh M. Al-Saif A. Meyer B. Pellucid marginal degeneration coexistent with cornea plana in one member of a family exhibiting a novel KERA mutation. Br J Ophthalmol. 2005; 89: 1538-1540 Crossref PubMed Scopus (16) Google Scholar This highly recognizable phenotype is due to homozygous mutation in KERA4 Pellegata N.S. Dieguez-Lucena J.L. Joensuu T. et al. Mutations in KERA, encoding keratocan, cause cornea plana. Nature Genet. 2000; 25: 91-95 Crossref PubMed Scopus (121) Google Scholar (causing lack of keratocan). The gene for the milder dominant form of cornea plana 6 Young R.D. Quantock A.J. Sotozono C. et al. Sulphation patterns of keratan sulphate proteoglycan in sclerocornea resemble cornea rather than sclera. Br J Ophthalmol. 2006; 90: 391-393 Crossref PubMed Scopus (8) Google Scholar is not known; this entity is likely what was labeled “peripheral sclerocornea” in the older literature. 1 Elliott J.H. Feman S.S. O'Day D.M. Garber M. Hereditary sclerocornea. Arch Ophthalmol. 1985; 103: 676-679 Crossref PubMed Scopus (44) Google Scholar , 2 Howard Ro Abrahams I.W. Sclerocornea. Am J Ophthalmol. 1971; 71: 1254-1258 Abstract Full Text PDF PubMed Scopus (29) Google Scholar Regarding the distinct phenotype of typical sclerocornea, the condition can be unilateral or bilateral and is characterized by a cornea that is completely opaque due to disorganization of the cornea's collagen architecture. 5 Sigler-Villanueva A. Tahvanainen E. Lindh S. et al. Autosomal dominant cornea plana: clinical findings in a Cuban family and a review of the literature. Ophthalmic Genet. 1997; 18: 55-62 Crossref PubMed Scopus (11) Google Scholar Corneal size can be small or normal. The cause of typical sclerocornea remains unknown; KERA analysis of several sporadic cases have been normal (unpublished results of the author).