Two brothers with reduced vision.

6-year-old boy and his 18-month-old younger brother presented to outpatient department with decreased vision and abnormal appearance of eyes since early childhood. They were otherwise healthy and born at term out of a consanguineous marriage. The best-corrected visual acuity in the elder brother was 6/12, N8 right eye and 6/36, N10 left eye with refractive error of + 7 D sph/+2 D cyl axis 90° in both eyes. Refractive error in his sibling was + 8 D sph/+2 D cyl axis 180° both eyes. In both children, ocular examination revealed small, horizontally oval corneas [8–9 mm horizontal diameter; [Figure 1] with wide limbal zone. There were superficial stromal central nebulomacular corneal opacities in both eyes without any associated vascularization. Intraocular pressures were normal with clear lens and clear red reflex posterior segment findings were with in normal limits.

Figure 1

Clinical photograph of case one showing central nebulomacular cornea opacity, horizontally oval and flat cornea

Questions

What is the differential diagnosis?

What additional test is required to confirm the diagnosis?

How will you manage these cases?

Answers

Differential diagnoses are:

Autosomal recessive form of cornea plana

Sclerocornea

Microcornea

Microphthalmos.

The presence of hypermetropia, corneal flattening, horizontally oval shape, wide limbal zone, central corneal opacity [Figures 1 and 3] with a history of consanguinity is highly suggestive of diagnosis of autosomal recessive form of cornea plana.

Figure 3

Clinical photograph of case two showing horizontally oval cornea with central nebulomacular cornea opacity

Axial lengths were 21.60 mm right eye and 21.42 mm left eye in first case. On manual keratometry (Bausch and Lomb), mires were distorted with an endpoint <36 D in both eyes

The patient was prescribed glasses and 6:1 full-time occlusion therapy was started. There was no additional improvement in vision with contact lenses. After 12 weeks of occlusion therapy, the left eye vision improved to 6/18p. Patient was advised squint surgery for left sided esotropia (Figure 2), which he refused.

Figure 2

Left esotropia in case one

In the second case, glasses were prescribed and alternate occlusion therapy was advised to prevent ametropic amblyopia. Improvement in vision was noticed by parents.

Discussion

Cornea plana is believed to occur in a mild autosomal dominant (CNAI) and a more severe autosomal recessive (CNA2) forms. Although the pathogenesis is unknown, the autosomal recessive form is known to be due to KERA mutation.[123] KERA encodes keratocan, a small leucine-rich proteoglycan. Keratocan is highly and uniquely expressed in the cornea.[123] Over 90% of cases are bilateral. Autosomal recessive variant is characterized by flat and horizontally oval cornea, high hyperopia, microcornea, wide limbal zone, marked arcus senilis, shallow anterior chamber, anterior synechiae, iris anomalies, and deep central corneal opacity.[123] Recessive cases can often be distinguished from the dominant ones by the presence of a central 5 mm of area of thickening and clouding. Vision in mild cases may be as good as 6/12 or 6/9 but considerably worse in recessive cases with central opacification. Glaucoma may occur in older individuals.

Conventional keratometry is usually done for confirmation of the diagnosis. Other distinguishing features include the horizontally oval corneal appearance and a normal or enlarged axial length. The usual refractive status is hypermetropia with astigmatism (as in these two cases) although myopia has also been described in eyes with marked axial lengthening. Appropriate refractive correction at younger age prevents development of sight threatening amblyopia and helps in visual rehabilitation. There are various issues with spectacle correction using high plus lenses such as poor cosmesis, restriction of peripheral visual field, magnification, and peripheral ring scotomata.

These problems can be overcome with the use of soft hydroxyethyl methacrylate lenticular contact lenses.

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