Keratoconus

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