Double Thinning: A Rare Case Series Of Patients With Coexisting Keratoconus And Pellucid Marginal Degeneration - What Are The Treatment Possibilities?

To study the ophthalmic features and treatment outcomes of patients with co-existing keratoconus(KC) and pellucid marginal degeneration(PMD).

A retrospective analysis of patients with co-existing KC and PMD in a tertiary care private eye hospital in Ernakulam, Kerala, India was performed from 2016 -2022.

Diagnostic criteria for the study included patients with slit lamp biomicroscopy examination showing signs suggestive of KC like central/paracentral stromal thinning, conical protrusion of cornea, stromal scars, Fleischer’s ring or Vogt’s striae along with an additional band of crescentic, peripheral, corneal thinning, typically located 1 to 2 mm from the corneoscleral limbus, associated with protrusion of the adjacent cornea, suggestive of a coexisting PMD in the same eye. Scheimpflug image and ASOCT confirmed the two areas of thinning.Topographic features were studied but not included in diagnostic criteria.Treatment outcomes were also studied. Thus,7eyes of 5 patients were enrolled in the study with a mean follow-up of 1.6 years.

 The average age was 37years and  60% were males.Majority (60%) had unilateral(UL) presentation with contralateral(CL) eye showing features of keratoconus.Schimeflug imaging and ASOCT showed double thinning in all cases.Topography was inept and did not show the classical findings of either disease. Treatment modalities employed were corneal collagen crosslinking(C3R) upto the limbus(1), penetrating keratoplasty followed by cataract surgery and intraocular lens implantation(1),large diameter deep lamellar keratoplasty(1), stabilization of cornea with inferior lamellar sclerocorneal graft followed customized corneal collagen crosslinking of the central cornea(1)and close follow up in rest.Early crosslinking of CL eye in UL cases was followed.

It is crucial to identify a coexisting PMD in patients with keratoconus as these patients may worsen despite C3R. Prior identification of dual ectasia helps in the accurate sizing of corneal grafts during corneal transplant procedures to include the additional band of inferior thinning. Early crosslinking of CL eye in UL cases is constructive.