Surgically induced keratoglobus in pellucid marginal degeneration

Corneal ectasia associated with posterior lamellar opacification

BACKGROUND

Concomitant corneal ectasia and posterior lamellar corneal opacification is rare, and the genetic relationship between these two conditions is unclear. We report the genetic and clinical characterization of this phenotype in three unrelated individuals.

MATERIALS AND METHODS

One previously reported affected individual and two unreported, unrelated, affected individuals were recruited for the study. Subjects and unaffected relatives underwent slit lamp examination, refraction, and multi-modal imaging. Saliva samples were obtained from two of the three affected individuals, from which DNA was extracted. Sanger sequencing was performed to identify mutations in genes associated with posterior amorphous corneal dystrophy (PACD), brittle cornea syndrome (BCS), and posterior polymorphous corneal dystrophy (PPCD), while copy number variation (CNV) analysis was used to identify CNV in the PACD locus.

RESULTS

Affected individuals demonstrated bilateral corneal steepening, stromal thinning and lamellar posterior corneal opacification. Corneal topography and tomography revealed conical or globular corneal steepening and decreased thickness. Anterior segment optical coherence tomography demonstrated hyperreflectivity of the posterior stroma in each of the affected individuals. Genetic testing did not detect a heterozygous deletion involving the PACD locus on chromosome 12 or a pathogenic mutation in the genes associated with BCS or PPCD.

CONCLUSIONS

Corneal ectasia may be associated with posterior lamellar stromal opacification that appears consistent with PACD. However, genetic testing for PACD as well as BCS and PPCD in affected individuals fails to reveal pathogenic deletions or mutations, indicating that other genetic factors are involved.

Keratoglobus

Keratoglobus is a rare noninflammatory corneal thinning disorder characterised by generalised thinning and globular protrusion of the cornea. It was first described as a separate clinical entity by Verrey in 1947. Both congenital and acquired forms have been shown to occur, and may be associated with various other ocular and systemic syndromes including the connective tissue disorders. Similarities have been found with other noninflammatory thinning disorders like keratoconus that has given rise to hypotheses about the aetiopathogenesis. However, the exact genetics and pathogenesis are still unclear. Clinical presentation is characterised by progressive diminution resulting from irregular corneal topography with increased corneal fragility due to extreme thinning. Conservative and surgical management for visual rehabilitation and improved tectonic stability have been described, but remains challenging. In the absence of a definitive standard procedure for management of this disorder, various surgical procedures have been attempted in order to overcome the difficulties. This article reviews the aetiological factors, differential diagnosis, histopathology, and management options of keratoglobus.

Kératoglobe : revue de la littérature

Keratoglobus is a rare bilateral condition characterized by a globular protrusion of the cornea. The cornea remains transparent and shows a generalized thinning, most pronounced in the periphery. Most often keratoglobus is a congenital disease, but it may be secondarily acquired. This corneal pathology causes severe visual impairment: it induces extreme myopia, irregular astigmatism, and corneal scarring due to previous hydrops. Spectacle corrections are utilized as long as they provide adequate visual function. Surgery is performed when visual needs are no longer satisfied. However, surgical management of this disease is difficult because of the extreme thinness of the entire cornea. Penetrating keratoplasty is one of the first surgical approaches to have been tested, but it has been partly renounced in favor of more complex procedures. Optimal surgical treatment for keratoglobus remains unknown because of the scarcity of reported surgical results.

Keratoglobus and posterior subcapsular cataract

We report sporadic, bilateral keratoglobus associated with posterior subcapsular cataract in a 43-year-old man. Slitlamp biomicroscopy showed symmetric arcus senilis-like deposits, a polygonal appearance resembling crocodile shagreen, an unusual endothelial appearance, and posterior subcapsular cataract. Orbscan II pachymetry maps (Bausch & Lomb) demonstrated bilateral diffuse corneal thinning (359.53 microm +/- 21.15 [SD] in the right eye and 379.61 +/- 11.49 microm in the left eye). These thickness values were confirmed by ultrasound pachymetry. In vivo confocal microscopy showed multiple criss-crossing dark lines and no identifiable cellular elements within the stroma. There were mild to moderate, guttata-like endothelial changes surrounded by pleomorphic cells. Phacoemulsification was performed in the left eye after careful consideration of the presenting features and modification of the surgical technique. Minimal structural alteration was observed during microstructural analysis 7 months after surgery. The endothelial morphology postoperatively was similar to that at baseline.