CHAPTER 20
Diseases of the Cornea, Anterior Segment, and Iris
This chapter discusses diseases of the cornea, anterior segment, and iris whose onset is during infancy and childhood. Familiarity with the embryology of the eye will help the reader better understand the developmental anomalies covered in this chapter (see BCSC Section 2, Fundamentals and Principles of Ophthalmology). Many of the disorders in this chapter are also discussed in BCSC Section 8, External Disease and Cornea.
Congenital and Developmental Anomalies of the Cornea
Abnormalities of Corneal Size and Shape
Abnormalities of corneal size and shape in childhood include isolated megalocornea, microcornea, keratoglobus, and keratoconus.
Megalocornea
Megalocornea is a nonprogressive enlargement of the cornea in which the diameter is 13 mm or greater. Megalocornea is a rare, usually bilateral, congenital condition. Inheritance is usually X- linked but may be autosomal recessive or dominant; 90% of affected patients are male. At birth, X- linked megalocornea is associated with iris transillumination and a deep anterior chamber. Late changes include corneal mosaic degeneration (shagreen), arcus juvenilis, presenile cataracts, and glaucoma. Treatment includes lubrication if patients have exposure keratopathy.
Microcornea
Microcornea is a clear cornea of normal thickness with a diameter less than 9 mm in the newborn and less than 10 mm after 2 years of age (Fig 20-1). Isolated microcornea is very rare. In microphthalmos, the entire eye is small and malformed, whereas in nanophthalmos, the eye is small but normal.
Figure 20-1 Microcornea, right eye.
Microcornea may be autosomal dominant or recessive. It usually accompanies other abnormalities of the eye, including cataracts, colobomas, high hyperopia, cornea plana, and persistent fetal vasculature. It may be seen in oculodentodigital syndrome, Warburg micro syndrome, and EhlersDanlos syndrome.
Keratoglobus
Keratoglobus is a very rare autosomal recessive, bilateral noninflammatory condition present at birth. It may occur in Ehlers-Danlos syndrome type VI. The corneal curvature is steep, with thinning of the cornea in the periphery and a very deep anterior chamber. Spontaneous breaks in Descemet membrane may produce acute corneal edema, and the cornea is easily ruptured by minor blunt trauma. Patients with keratoglobus should routinely wear protective lenses. Scleral contact lenses may be helpful.
Keratoconus
In keratoconus, the central or paracentral cornea bulges and progressively thins such that the cornea takes on the shape of a cone. Keratoconus may present and progress during the adolescent years. It can occur with Down syndrome, atopic diseases, and chronic eye rubbing. Keratoconus may be familial. Unlike in keratoglobus, iron lines, stress lines (Vogt striae), and apical scarring are often seen. Tears in Descemet membrane can cause acute corneal edema (hydrops) in patients with keratoconus.
Abnormalities of Peripheral Corneal Transparency
Posterior embryotoxon
Posterior embryotoxon, also called a prominent Schwalbe line, is a thickening and anterior displacement of the Schwalbe line. This anomaly is visible at the slit lamp; it looks like an irregular white line just concentric with and anterior to the limbus (Fig 20-2). Through the gonioscope, the condition looks like a continuous or broken ridge protruding into the anterior chamber. Pigmented spots may be seen on the internal surface of the ridge. This anomaly is most often associated with Axenfeld-Rieger syndrome but is also found in arteriohepatic dysplasia (Alagille syndrome) and velocardiofacial syndrome (22q11 deletion syndrome); it may be an isolated finding in 15% of normal patients.
Figure 20-2 Posterior embryotoxon (arrow) in Axenfeld-Rieger syndrome.
Cornea plana
Cornea plana is a rare, bilateral, often autosomal recessive condition that features flat corneas, peripheral scleralization of the cornea, and a shallow anterior chamber. Patients are often hyperopic, and glaucoma may develop secondary to angle closure due to the shallow anterior chamber. Refractive correction and glaucoma management are the mainstays of treatment.
Epibulbar dermoid
An epibulbar (limbal) dermoid is a choristoma composed of fibrofatty tissue covered by keratinized epithelium. It is present from birth, and little if any postnatal growth occurs. Dermoids may contain
hair follicles, sebaceous glands, or sweat glands. They can be up to 10 mm in diameter and usually straddle the limbus. They may extend into the corneal stroma and adjacent sclera but seldom occupy the full thickness of either cornea or sclera. Most epibulbar dermoids are on the inferior temporal limbus. Many produce a lipoid infiltration of the corneal stroma at their leading edge. They are sometimes continuous with subconjunctival dermolipomas that involve the lateral quadrant of the eye.
Epibulbar dermoids can produce anisometropic astigmatism with secondary amblyopia. Large epibulbar dermoids can cover the visual axis. Removal of epibulbar dermoids may be indicated if they cause ocular irritation or amblyopia. Surgical excision may result in scarring and astigmatism, which can also lead to amblyopia. Although excision will not eliminate the preexisting astigmatism, surgery may be useful for treating very elevated lesions (Fig 20-3). Tumor removal involves excising the episcleral portion flush with the plane of surrounding tissue. In general, the surgeon need not remove underlying clear corneal tissue, mobilize surrounding tissue, or apply a patch graft over the resulting surface defect; however, because some lesions extend into the anterior chamber, tissue should be available in the event that a patch graft is required. Cornea and conjunctiva heal within a few days to several weeks, generally with some scarring and imperfect corneal transparency; nevertheless, the appearance can be improved considerably.
Figure 20-3 Epibulbar dermoid with hair growing in the center. (Courtesy of Ken K. Nischal, MD.)
Epibulbar dermoids are often seen with Goldenhar syndrome (oculoauriculovertebral spectrum; see also Chapter 18). These patients may have a variety of other anomalies, including ear deformities (Fig 20-4), maxillary or mandibular hypoplasia, vertebral deformities, eyelid colobomas, and Duane retraction syndrome.
