2020–2021 BCSC Basic and Clinical Science Course™
6 Pediatric Ophthalmology and Strabismus
Part II: Pediatric Ophthalmology
Chapter 21: Disorders of the Anterior Segment
Disorders of the anterior segment include a wide spectrum of conditions involving the cornea, iris, anterior chamber angle, and lens. Pediatric glaucoma and lens disorders are discussed in Chapters 22 and 23, respectively. Anatomy of the anterior segment and its development are discussed in BCSC Section 2, Fundamentals and Principles of Ophthalmology. See also Section 8, External Disease and Cornea, for detailed discussion of some of the disorders covered in this chapter.
Abnormalities of Corneal Size or Shape
Primary megalocornea is characterized by bilateral congenitally enlarged corneas, with an increased horizontal corneal diameter and a deep anterior chamber (Fig 21-1); it is often associated with iris transillumination. On biometry, the ratio of anterior chamber depth to total axial length is typically 0.19 or greater, a feature that is useful for distinguishing this anomaly from buphthalmos. Late changes include corneal mosaic degeneration (shagreen), arcus juvenilis, presenile cataracts, and glaucoma. The phenotype is often caused by X-linked recessive mutation in CHRDL1. Secondary megalocornea is typically a result of increased intraocular pressure.
Figure 21-1 Megalocornea. The depth of the anterior chamber in this male infant was more than 19% of total axial length, a feature that is useful for distinguishing the anomaly from buphthalmos.
(Courtesy of Arif O. Khan, MD.)
Davidson AE, Cheong SS, Hysi PG, et al. Association of CHRDL1 mutations and variants with X-linked megalocornea, Neuhäuser syndrome and central corneal thickness. PLoS One. 2014; 9(8):e104163.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.