Dr. Mohammad Amiri , ODDepartment of Optometry ,Faculty ofRehabilitationShahid Beheshti Medical Sceince UniversityVision Care of MeniconKeratoconusAnd specialty contact lens fitting of irregularcorneas
Keratoconus• Is a progressive disorder in which the cornea has irregular shape• Onset: around puberty• Autosomal dominant• Usually bilateral; but assymetrical• Systemic association: e.g. Down syndrome; Turner syndrome; Marfan syndrome• Ocular association: e.g. retinitis pigmentosa; vernal keratoconjunctivitis;
• According to morphology can be classified into• Nipple cones: small size 5mm; steep curvature; the apex of the cone is central or infero-nasally
• Presentation: visual impairment due to progressive myopia & astigmatism (usually reported for one eye); changes in spectacle Rx; decrease tolerance to contact lens wear;• Signs: central or paracentral stromal thinning; apical protrusion; irregular astigmatism; steepening of the cornea graded according to keratometry readings (mild <48D, moderate 48-54D, severe >54D) Early in the disease: oil droplet reflex on ophthalmoscopy; irregular scissor reflex on retinoscopy; Vogt lines (i.e. deep vertical stromal striae) on slit- lamp exam; irregular astigmatism on keratometry; abnormal corneal topography
Keratoconus CharacteristicsNon-inflammatory.Central or para-central corneal thinning.Corneal steepening or protrusion.Increased astigmatism and possibly myopia.Loss of best spectacle corrected visual acuity.Corneal striae and scarring.Corneal hydrops (inflammatory).
Keratoconus• Non-Inflammatory Ectasia • Stromal Thinning • Disruption of Bowman’s Membrane• Corneal Ectasia • Myopia • Irregular Astigmatism• Optical Correction • Spectacles– early • Contact Lenses– later
Keratoconus• Demographics • Estimates vary from 50 to 170 per 100,000• Obscure Etiology • Heredity • Allergies, Eye Rubbing
Why Does the Cornea Bulge in Keratoconus?• Corneal tissue is abnormal • Too elastic? • Abnormal cross-linking of collagen?• Loss of structural integrity of Bowman’s Layer?• Keratocyte apoptosis • Trauma (eye rubbing)• Corneal tissue bulges because it is too thin?
Pathology of Keratoconus Loss of Bowman’s Layer. Stromal Thinning. Apoptosis. Increased Enzyme Activity. Enlarged Prominent Corneal Nerves.
Causes of Keratoconus• Heredity vs. Mechanical• Cellular• Tissue• Genetic
Cellular Changes• Keratoconus cells are hypersensative.• Increased enzyme activity, lack of enzyme inhibitors.• Matrix substrate instability in response to environmental stress factors.• mtDNA damage and exaggerated oxidative response causing cellular damage.
Tissue Changes Loss of Bowman’s layer. Lamellar slippage. Lack “anchoring” lamellar fibrils. Apoptosis of the stroma causing anterior thinning.
Heredity vs. Mechanical• Does eye rubbing cause Keratoconus?• 2 out of 250 doctors feel that rubbing is a cause.• KC patients do rub their eyes more often than those without KC.• What is it that makes KC patients rub their eyes?
Genetics• Autosomal dominant w/variable penetrance.• SOD1, an antioxidant enzyme, is abnormal in some KC corneas.• No single gene responsible.• 10 different chromosomes have been associated with KC.• Most likely multiple genes involved.
Additional InformationMale to Female Ratio = 3:1Approximately 20% result in PKP.90% are diagnosed by optometrists.Mean age of diagnosis is 22.88 years.Visual outcome with RGP is better than PKP.More prevalent in certain ethnic groups (4x higher in Asians from Indian sub-continent regions than White Europeans).
Progression and PrognosisAge is a big factor.The younger the diagnosis, the poorer the prognosis.Less likely to progress to the point of a transplant if diagnosed in the 30’s.20% of Keratoconus patients result in corneal transplants.35 to 45% of all transplants are due to Keratoconus.
Types of Keratoconus• Nipple/Oval cone - central or mildly para- central localized thinning and steepening.• Keratoglobus - Large generalized thinning and steepening.• PMD (pellucid marginal degeneration) – peripheral thinning and steepening.• Keratoconus Fruste – Less progressive and less manipulative.
Nipple/Oval Cone• Central Steepening• Steepest form
Keratoglobus• Wider – 75 to 90% of cornea.• Not as steep.
How to Treat Keratoconus Spectacles Contacts Soft Standard Soft Custom RGP Standard RGP Custom Hybrid Surgery Intacs Penetrating Keratoplasty Riboflavin/UV treatment
When to Intervene?• Best Spectacle/Soft CL Acuity 20/30 or better? – Good tolerance of acuity. – Corneal health is not compromised. – “If it aint broke, don’t fix it.”• Best Spectacle/Soft CL Acuity worse than 20/30? – Specialized contact lenses. – My opinion, use RGP lenses.
Which RGP Design?• Early Keratoconus – Standard RGP – KC RGP• Mid-stage Keratoconus – KC RGP – Custom KC RGP• Advanced Keratoconus – Custom KC RGP – Intra-limbal or Scleral RGP
My “GO TO” Lens – Rose K• Developed by Dr. Paul Rose.• Designed to fit the irregular cornea.• “Very forgiving lens”• Multiple designs to fit all shapes of corneas and corneal conditions.• Blanchard is very good to work with and has staff to assist with very difficult cases.
Nipple/Oval Cone Fitting• Most common form of KC.• Early stages - simple RGP or KC RGP• Later stages – KC RGP usually small and steep.• The steeper the cone, the smaller the lens diameter.
Rose K2• Rose K vs. Rose K2• 72% of patients notice an increase in acuity with aspheric, aberration control.• Lens to be centered on the cone.• Reduce excessive movement (1 to 2mm).
Fitting the Rose K2• Too high – tighten edge lift reduce OAD steepen base curve• Too low – increase edge lift increase OAD flatten base curve
Fitting the Rose K2• Centrally fitting the lens on a nipple cone better insures optimal acuity and comfort.
Rose K2IC• IC stands for irregular cornea• Larger diameter• Larger optic zone• Aspheric for aberration control• Reverse geometry design
Fitting with ACTUsing ACT ( Asymmetric Corneal Technology) • 3 standard grades available • Option also to specify degree of tuck in 0.1 steps from 0.4 to 1.5mmGrade 1 ( 0.7mm steeper) Grade 3 (1.3mm steeper) Grade 2 (1.0mm steeper)
Fitting with ACTACT - Improved comfort , lens stability and vision NO ACT WITH ACT
Fitting Pearls Tendency to tighten after initial fitting. Light central touch will increase acuity. Avoid central staining. Movement is necessary but slight movement is usually sufficient. Pay attention to tear flow beneath lens. The steeper the lens, the smaller OAD and less movement. Don’t change too many parameters at once.
Penetrating Keratoplasty When to refer? Acuity is 20/50 or worse. Patient intolerance to visual decrease. Scars within the visual axis. Multiple episodes of Hydrops. Contact lens intolerance. Unable to get adequate/healthy CL fit. Consider OD to OD referral. Give reasonable expectations.
Post PKP Management• How soon can you fit with lens?• Why are the curvatures so strange?• Do you have to wait for all sutures to be removed?• Corrective options. – Spectacles – RGP contact lenses. – LASIK
Rose K2 Post Graft Much more difficult to fit than KC. Patients are less tolerable to CL. Eyes are more dry. Ill-fitting contact lenses can lead to graft rejection. Lens design is crucial to success.
K2PG Fitting Pearls• Don’t be intimidated!• Watch tear flow!• Also good lens for ectasia patients.• Stay with your fitting basics – Fit base curves. – Adjust diameter. – Adjust peripheral curves. – Use ACT or Toric PC if needed.