Keratoglobus is strongly associated with blue sclerae and Ehlers-Danlos syndrome type VI (see Chapter 8), and it may represent a defect in collagen synthesis. Histologically, it is characterized by an absent or fragmented Bowman layer, thinned stroma with normal lamellar organization, and a thin Descemet membrane. Unlike keratoconus, keratoglobus is not associated with atopy or hard contact lens wear.
The corneas have a globular shape with a deep anterior chamber. The corneal curvature may be as steep as 50–60 D, and generalized thinning appears, especially in the periphery. This is in contrast to keratoconus, which typically has inferior paracentral thinning and protrusion with thinning at the apex. Spontaneous rupture of the Descemet membrane and corneal hydrops can occur, but iron lines, stress lines, and anterior scarring are not typically seen. The corneal diameter may be slightly increased. Fleischer rings are usually not present, but prominent folds and areas of thickening in Descemet membrane are common.
Contact lenses, especially scleral lenses, may be of benefit. The prognosis for PK is much poorer in keratoglobus than in the other corneal ectasias. Tectonic lamellar keratoplasty followed by PK could be considered in cases requiring intervention to maintain functional vision. Spontaneous corneal rupture has been reported; thus, patients must be counseled regarding the importance of protective eyewear. High myopia is treated with spectacles to prevent amblyopia in children.
Feder RS, Neems LC. Noninflammatory ectatic disorders. In: Mannis MJ, Holland EJ, eds. Cornea. Vol 1. 4th ed. Philadelphia: Elsevier; 2017:820–843.
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.