Article Text

Cornea plana—clinical features, videokeratometry, and management
  1. M P GAVIN,
  2. C M KIRKNESS
  1. Tennent Institute of Ophthalmology, Western Infirmary, 38 Church Street, Glasgow G11 6NT
  1. Dr M P Gavin.

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Editor,—Cornea plana is a rare anomaly in which the corneal radius of curvature is larger than normal producing high hypermetropia with astigmatism and poor acuity in most cases. Myopic astigmatism can also occur. We describe three patients with this anomaly including videokeratometry images.

CASE REPORTS

Case 1

A 25 year old woman complained of a deterioration in visual acuity over recent years. Her parents, three brothers, and an older sister (examined by the authors) had no manifest ocular problems.

Corrected visual acuities were 6/24, N24 right eye and 6/60, N24 left eye with refractive errors of −2.25/+1.50 × 165° and −7.50/+2.50 × 20° respectively. Examination revealed apparently small corneas with peripheral opacification—particularly superiorly (Fig 1)—giving a horizontally oval configuration. There was central stromal thickening and faint opacity (Fig 1). Automated videokeratoscopy confirmed marked corneal flattening with regular astigmatism (Fig 2). There were no abnormal features affecting the iris or crystalline lens. The intraocular tensions (Goldmann tonometry) were right eye 11 mm Hg and left eye 10 mm Hg. Gonioscopy demonstrated open drainage angles with normal angle structures. Axial lengths were 26.90 mm right eye and 26.95 mm left eye. Funduscopy revealed healthy maculas and bilateral peripapillary chorioretinal degeneration consistent with marked axial myopia. She is managing well with a low visual aid but no additional improvement in vision could be achieved with contact lenses.

Figure 1

Right eye of case 1 shows the peripheral corneal changes of superficial pannus and deeper stromal opacification (left). There was also deep stromal opacification and thickening in the central cornea (right).

Figure 2

Computer assisted videokeratometry maps of case 1 showing marked flattening (see colour coded scale bar) with the characteristic “bow tie” pattern seen with regular astigmatism.

Case 2

A healthy 13 month old girl was noted to have bilateral corneal “haze” and a left exophoria of approximately 20 prism dioptres with and without optical correction. Examination under general anaesthesia showed refractive errors of +6.50/+2.00 × 110° right eye and +8.50/+2.00 × 70° left eye. Both corneas were small and horizontally oval with vertical corneal diameters of 8.75 mm right eye and 9.50 mm left eye. There was superficial pannus and deeper stromal opacification of the peripheral cornea and faint stromal opacification centrally. Intraocular pressure was 10 mm Hg in both eyes. The lenses, irides, and fundi were healthy. She was lost to follow up and was re-referred aged 4 years with manifest left convergent strabismus. Acuities were right eye 6/18, left eye 4/60 (Kay’s pictures). Cycloplegic refraction revealed a refractive error of +5.50 DS in both eyes. Glasses were prescribed. Two months later the squint was much improved but acuity remained poor in the left eye—right eye 6/9, left eye 2/60 (Sheridan–Gardner test), and occlusion has been commenced.

Case 3

The 13 year old elder brother of case 2. Best corrected acuities were right eye 6/9, N5 and left eye 6/18, N5 with refractive errors of +7.50/+1.75 × 90° and +8.50/+1.75 × 110° respectively. He was orthophoric with good binocular function. Both corneas appeared horizontally oval with circumferential peripheral opacification. Vertical corneal diameters were 7.12 mm. There was superficial corneal opacification centrally but no vascularisation or thickening (Haag–Streit pachymeter readings: 0.42 mm right eye, 0.40 mm left eye). Both anterior chambers were moderately shallow. The drainage angles were open with no abnormal features. Intraocular pressures were normal.

Axial lengths were 23.15 mm right eye and 23.40 mm left eye. Computer assisted videokeratoscopy imaging revealed marked, bilateral corneal flattening (more prominent centrally) with regular astigmatism.

COMMENT

Cornea plana was first described by Rubel in 1912.1 It is more often described along with the more common entity, sclerocornea,2 in which there is peripheral opacification and vascularisation of the cornea. In cases with sclerocornea only a proportion are associated with an enlarged radius of curvature of the central cornea, cornea plana. Over 90% of cases are bilateral.3 The peripheral corneal vascularisation may be superficial or deep and appears to be non-progressive. Differential diagnosis includes microphthalmia and microcornea.4

Conventional keratometry confirms the diagnosis but computer assisted videokeratometry has not been described previously. Other distinguishing features of the condition include the horizontally oval corneal appearance and a normal or enlarged (as in case 3) axial length. The usual refractive status is hypermetropia with astigmatism (cases 1 and 2) although myopia has also been described in eyes with marked axial lengthening.5

The gene responsible for cornea plana has recently been assigned linkage to the long arm of chromosome 12. This represents an exciting development in our understanding of this anomaly.6

Failure to diagnose and correctly manage individuals with cornea plana at an early age can result in the development of ametropic amblyopia.7 Careful orthoptic assessment is vital (as demonstrated by case 1). There are several problems with spectacle correction using high plus lenses—poor cosmesis, restriction of peripheral visual field, magnification and peripheral ring scotomata—so rigid contact lenses, which overcome these optical problems, have been used with some success although the extreme corneal flattening in this condition can lead to a poor, unstable fit. This problem can be overcome (as in case 2) with the use of a soft (HEMA) lenticular contact lenses.8 Penetrating keratoplasty has been advocated in a previous report9 but seems unnecessary as contact lenses achieve good visual and cosmetic outcomes.

References

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