In the largest case series on posterior keratoconus to date, researchers in India conducted a retrospective study to describe the varied presentations of posterior keratoconus. Diagnosing this rare condition requires a high index of suspicion, thorough slit-lamp examination, and whole-body evaluation to rule out other associated anomalies.
This study, published in Cornea, looked at 12 patients — 7 males and 5 females — spanning 3 years. Ocular and systemic examinations were performed, including best corrected visual acuity, automated keratometry, slit-lamp examination, Scheimpflug tomography, and anterior segment optical coherence tomography were performed.
Investigators found that all but 1 patient had unilateral posterior keratoconus. All patients had nebular opacity, with an underlying posterior concavity. Iris nubbing was present in 6 cases (50%) and Fleischer ring was present in 6 cases (50%). Fundus examinations were found to be normal in all patients. Best corrected visual acuity for the group ranged from 20/200 to 20/60 in 5 eyes (58.3%) and less than 20/200 in 4 eyes (33.3%).
A 12-year-old female, presented with systemic manifestations. Another 7 — all middle-aged adults — had superior, central, or peripheral excavation. Microcornea was noted in 2 patients.
According to the study’s authors, a thorough slit-lamp examination is necessary for diagnosing posterior keratoconus since it can be missed due to its subtle manifestations. Specifically:
- Look for atypical posterior concavity in the cornea with ectasia of the overlying stroma.
- The anterior surface of the cornea also may be involved and become irregular due to stromal scarring.
- Corneal topography will show a central steepened “cone” coincident with the area of circumscribed posterior keratoconus and paracentral flattening.
- A detached Descemet membrane underlying the area of excavation can be identified.
In most cases, vision is not affected in peripheral lesions. Treatment options can include refractive correction with glasses or contact lenses to prevent amblyopia. Pupillary dilation, sector iridectomy, rotational corneal autograft, or penetrating keratoplasty may be performed to reduce opacity. Deep anterior lamellar keratoplasty may help flatten the posterior excavation, reduce astigmatism, and eliminate stromal haze.
Posterior keratoconus is a rare, noninflammatory disease of the cornea with increased curvature of the posterior corneal surface. It is usually marked by nebular corneal opacity with posterior concavity and ectasia of the overlying stroma. While usually unilateral and nonprogressive, posterior keratoconus can be bilateral in rare cases. Because it can be linked to systemic disorders, diagnosing the condition is crucial.
The disorder develops when the primary pupillary membrane and the corneal endothelium do not adhere properly, which probably impacts the development of overlying corneal stroma. Because iris adhesions and corectopia have been observed in some patients in previous studies, it has been concluded that congenital posterior keratoconus is a part of the spectrum of anterior chamber cleavage syndromes. The condition also can occur after a trauma, such as a metallic oblique-penetrating injury.
In the eye, posterior keratoconus can cause aniridia, anterior lenticonus, anterior polar cataract, ectopia lentis, ectropion uveae, glaucoma, iris atrophy, iron lines in the epithelium, optic nerve hypoplasia, posterior polymorphous dystrophy, ptosis, and retinal coloboma. Several systemic abnormalities also have been associated with the condition, including brachydactyly, broad flat nasal bridge, webbed neck, cleft lip/palate, genitourinary anomalies, growth retardation, mental retardation, and hypertelorism.
Ganesan N, Narayana S, Kasturi N, Kaliaperumal S, Srinivasan R, Vallinayagam M. Varied presentations of posterior keratoconus: a clinical case series. Cornea. 2020;39(11):1348-1353. doi: 10.1097/ICO.0000000000002455.