keratoconus
TRANSCRIPT
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By: Marika Mohammed
Keratoconus
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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?
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Primary- irregular astigmatism - myopia
Secondary- corneal scarring
Visual Loss
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Presents at puberty or early adulthood
50-230 per 100,000
Equal prevalence in both sexes and all races
Epidemiology
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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
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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
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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
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Symptoms:Progression until 4th decadeAsymmetric visual complaintsBlur and distortions Glare/flareMonocular diplopia Photophobia Initial correction by spectacles then soft
contact lenses
Clinical Features
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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
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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
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Vogt Striae
Corneal HydropsMunson’s Sign
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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
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Maps the corneal curvatureIndicates any distortions or scarring Common characteristics:
Asymmetrical bowtieInferior corneal steepening Skewed radia axes
Corneal Topography
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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
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Amsler-Krumeich Classification
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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
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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)
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Thank you!
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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