KERATOCONUS

WHAT IS KERATOCONUS?

 

 

 

Kertoconus is a rare, inherited eye disease which affects approximately 1 in 7000. The cornea starts to progressively get thinner and begins to bulge outwards.  It is the conic deformity which prevents light from coming through the lens undistorted.  When light enters the eye, it cannot focus properly and this results in blurry vision.  The progressive, bilateral thinning of the cornea causes irregular astigmatism and possible perforation. This optical problem may be corrected with contact lenses but may eventually require a corneal transplant or Keratoplasty.

 

Keratoconus begins in adolescence, usually with one eye first then goes through various stages of remission and relapse before stabilizing around the age of 40-45.  Both females and males are equally affected.  The irregularity of the cornea makes the vision so hard to correct.  If left untreated, this disease may cause permanent vision loss requiring corneal transplantation.

 

 

This disease can be classified by the degree of conicity of the apex of the cornea:

 

STAGES OF ADVANCEMENT OF KERATOCONUS:

 

Stage 1- Oblique astigmatism is noted

Stage 2- Vision is not refractable to normal

Stage 3- Pronounced conical shape with corneal thinning

Stage 4- Opacities at the apex

Mild:  (up to 45D), moderate (between 45 and 52D), advanced (between 52 and 60D) and severe (over 60D)

 

SIGNS AND SYMPTOMS OF KERATOCONUS

 There are three associated conditions of Keratoconus

a.)  Munson Sign:  cone visible when eye looks downward, eye protrudes in lower lid

b.)  Fleisher’s Ring:  Rust colour ring—iron deposits at base of cornea in corneal epithelium

c.)   Hydropes:   abnormal and sudden gathering of fluid after Descemet’s membrane and endothelium break--The fluid accumulates in the corneal tissue

·        Blurred vision with glasses—inability to correct    vision in young person to 20/20 with spectacles

·        frequent prescription changes

·        vertical straie

·        Distorted keratometer mires

·        high astigmatism

·        central corneal thinning

·        oblique axis

·        small mires

·        asthenopia

 

Rigid gas permeable (RGP) contact lenses are commonly used to aid in the correction of keratoconus.   RGP lenses are generally well tolerated and have a high success rate.  However, they don’t work for all patients since some patients are not comfortable with the fit and depending on the stage of advancement of the disease, RGP lenses may cause discomfort and compromise the corneal integrity.  This would mean the patient would need to seek alternative options for this condition. 

An alternative to the RGP lenses is the piggyback system of fitting contact lenses.  This system consists of a rigid gas permeable lens placed on top of a soft contact lens.  This method of fitting was first introduced in the early 1970s for patients who could not tolerate RGP or scleral lenses.  At that time, limited options were available to patients consisted of mainly low DK lenses that resulted in corneal hypoxia.