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By: Marika Mohammed
Keratoconus
Progressive, non-imflammatory ectatic disorder of the cornea
Usually bilateral but asymmetric
Paraxial stromal thinning and weakening leading to corneal surface distortion
What is it?
Primary- irregular astigmatism - myopia
Secondary- corneal scarring
Visual Loss
Presents at puberty or early adulthood
50-230 per 100,000
Equal prevalence in both sexes and all races
Epidemiology
Generally unknown, likely multifactorial Suspected:
Family history in 6-8% of casesx15-67 higher incidence if first degree relative Eye rubbingContact lens use Systemic disorders eg. Downs Syndrome,
Ehlers-Danlos, Osteogenesis Imperfecta
Aetiology
All layers of the cornea believed to be affected
Epithelial cells may be enlarged and elongated
Early degeneration of basal epithelial cells
Disruption of basement membrane
Pathophysiology
Growth of epithelium posterior to Bowman’s layer forming z-shaped interruptions or breaks
Scarring of Bowman’s layer and anterior stroma
Stromal thinning due to normal-sized fibres but low numbers of llamelae
Symptoms:Progression until 4th decadeAsymmetric visual complaintsBlur and distortions Glare/flareMonocular diplopia Photophobia Initial correction by spectacles then soft
contact lenses
Clinical Features
Signs:Slit lamp:
Fleisher ring: Iron deposits in epithelial layer at cone base
Vogt striae: Vertical stress lines at thinnest part of cornea
Central and inferior paracentral corneal thinning
Corneal scarring
Scissor reflex on retinoscopy due to irregular astigmatism
Rizzutti’s sign: conical reflection on the nasal cornea when light is shone temporally
Munson’s sign: corneal protrusion may cause angulation of the lower lid on downgaze (advanced)
Corneal Hydrops: stromal edema due to leakage of aqueous through a tear in descemet membrane
Vogt Striae
Corneal HydropsMunson’s Sign
Complete history and clinical examinationVisual acuity testingSlit lamp examinationRetinoscopy- for scissoring reflexKeratometry- may demonstrate irregular
mires and progressive corneal steepeningDiagnostic rigid contact lenses Corneal Topography
Diagnosis
Maps the corneal curvatureIndicates any distortions or scarring Common characteristics:
Asymmetrical bowtieInferior corneal steepening Skewed radia axes
Corneal Topography
K value – Measures central steepening of the cornea; ≥ 47.20 D suggests keratoconus
I-S value – Measures inferior-versus-superior corneal dioptric asymmetry; ≥ 1.4 D suggests keratoconus
KISA% - Incorporates K and I-S values quantifying regular and irregular astigmatism into a single index; 60-100% suggests keratoconus, ≥ 100% strongly suggests frank keratoconus
Rabinowitz diagnostic criteria
Amsler-Krumeich Classification
Non-Surgical:Spectacle correction- early, as long as visual
acuity allowsContact lens-
With progressive astigmatismSoft-tonic initiallyRigid gas-permeable lenses most common Until corneal irregularity becomes too
advancedCollagen cross-linking
Management
Surgical:Intrastromal corneal ring segments:
thin, semi-circular plastic inserts implanted into the mid-corneal layers to flatten the cornea
Keratoplasty – 10-15% patients penetrating keratoplasty (full thickness corneal
transplant) : most commonDeep anterior lamellar keratoplasty (partial
thickness corneal transplant)
Thank you!
References 1. Espandar L, Meyer J. Keratoconus: Overview and Update on
Treatment. Middle East Afr J Ophthalmol [Internet]. 2010 [cited 9 January 2015];. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2880369/
2. Wayman L, Trobe J, Park L. Keratoconus. [Internet]. 2014 [cited 9 January 2015];. Available from: http://www.uptodate.com.ezproxy.sastudents.uwi.tt:2048/contents/keratoconus?source=search_result&search=keratoconus&selectedTitle=1~13
3. Weissman B, Roy H. Keratoconus [Internet]. Medscape. 2014 [cited 9 January 2015]. Available from: http://emedicine.medscape.com/article/1194693-overview#showall
4. Romero-Jiménez M M, Santodomingo-Rubido J, Wolffsohn J. Keratoconus: a review. Elsevier [Internet]. 2010 [cited 9 January 2015];. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20537579
5. OphthaClass. Amsler-Krumeich Classification for Grading Keratoconus - OphthaClass [Internet]. 2015 [cited 9 January 2015]. Available from: http://ophthaclassification.altervista.org/krumeichclass/
6. Sinjab M. Quick Guide to the Management of Keratoconus A Systematic Step-by-Step Approach. New York: Springer; 2012.
References