This month’s issue features articles on managing patients with corneal distortion. Patients can have an irregular astigmatism secondary to trauma, inflammation, or an acquired/hereditary condition, such as a non-inflammatory thinning disorder.
Differential of non-inflammatory thinning disorders is an important goal in order to best manage these challenges from a patient expectation perspective and effectively neutralize the irregular cornea.
• Keratoconus: A non-inflammatory condition where the cornea is conical because of protrusion and thinning, treatment can vary for these conditions.1,2
Keratoglobus, pellucid marginal degeneration (PMD) and posterior keratoconus are other thinning disorders that you may encounter in your clinical practice. Each can closely resemble keratoconus, and a few may even be different clinical manifestation of the same underlying problem.1 Additionally, other clinical fascinations can exist and have characteristics of non-inflammatory thinning of the cornea (dellen, marginal furrows and post-irradiation thinning).1,3
• Keratoglobus: Although genetically related, keratoglobus differs from the minimally progressive keratoconus. Scarring is rarely seen and iron lines are not found.1 The thinning is diffuse and more significant in the periphery (even the scleral region) as compared to the axial thinning in keratoconus. Effective management requires neutralizing irregular astigmatism and distortion by using rigid lenses.
• Pellucid Marginal Degeneration: PMD is often confused with keratoconus because it carries most of the distinguishing characteristics of the rest of the thinning disorders. There is significant inferior thinning to the periphery and an uninvolved zone between the thinned section of the cornea and limbus. There is no iron line or lipid deposition.1 Corneal scarring is rarely found. Subtle topographic differences may clinically exist. Jay Pepose, M.D., Ph.D., and co-workers assessed higher-order aberrations with wavefront technology and found greater amounts of vertical coma in keratoconus and trefoil in patients with PMD.3
Other corneal diseases to consider include Terrien’s corneal degeneration and Mooren’s ulcers.1
• Posterior Keratoconus: This condition is characterized as a developmental anomaly by a total or localized thinning, without any protrusion of the anterior corneal surface. Corneal guttata is common and variable stromal scarring is possible.1 Surprisingly, this disease is often unilateral and non-progressive. It is not as devastating to vision as keratoconus due to the location of the distortion; often no treatment is required.1
Treatment can vary. For example, neutralizing the irregular astigmatism (ectasia) with rigid lenses (corneal GPs, sclerals and hybrids), early intervention with collagen crosslinking to help stabilize the cornea or surgical remedies (such as corneal Intacs and keratoplasty) are all possible treatments. Additionally, lamellar surgery—where only the Descemet’s membrane and endothelium remain intact—has recently gained acceptance in lieu of full thickness grafting. Intralase enhanced surgeries for Intacs and corneal grafting have also gained acceptance. Graft beds made with the Intralase technology—using exotic shapes—allow for a shortened healing time, for quicker suture removal and may strengthen the cornea.
Don’t forget to carefully look for retinal pathology in keratoconus patients. A recent case series showed a relatively high rate of symptomatic and asymptomatic retinal breaks in keratoconus patients: 13% of patients we enrolled in the Collaborative Evaluation in Keratoconus study had retinoprexy, or required close monitoring for new retinal breaks. A French study also showed a longer than expected axial length in keratoconus.
Take advantage of the plentiful options available to us today for managing these often challenging cases. Considering the viable options after a careful analysis of presenting signs and features will definitely aid in effectively caring for patients with thinning disorders, even though the treatment options may not differ significantly among the conditions.
1. Krachmer JH, Feder RS, Belin MW. Keratoconus and related non-inflammatory thinning disorders. Surv of Ophthalmol. 1984 Jan-Feb;28(4):293-322.
2. Lass JH, Lembach RG, Park SB, et al. Clinical management of keratoconus: A multicenter study. Ophthalmol. 1990 Apr;97(4):433-45.
3. Pepose J. Wavefront aberrations in patients with keratoconus and pellucid marginal degeneration. Invest Ophthalmol Vis Sci. 2004;45:e-abstract 2893.