By Sanjay Kumar Mishra, M. Optom
The word keratoconus is formed by two Greek words; kerato, meaning cornea and konos, meaning cone. Keratoconus is condition in which the shape of the cornea which usually round is distorted, developing a cone - shaped bulge, resulting in decreased or distorted vision.
In other words keratoconus is a non-inflammatory corneal thinning disorder which result in conical protrusion of the cornea .Keratoconus is a thinning disorder of the cornea that leads to conical ectasia the thinning and conical protrusion of the cornea in keratoconus typically result in irregular astigmatism.
Causes of keratoconus:-
The pathophysiology of how keratoconus develops and progress is not well understood. Genetic factors appear to be multi factorial and are considered fundamental to the etiology and progression of keratoconus. However, the underlying molecular and /or genetic abnormalities are unknown.
Keratoconus has been linked with systemic conditions such as atopic disease, genetic conditions such as trisomy 21 and Turner's syndrome, and various connective tissue disorders, as well as with eye rubbing, RGP lens wear and ocular trauma.
Keratoconic corneas also have an accumulation of cytotoxic by products from the nitric oxide and lipid peroxidation pathways, abnormal antioxidant enzymes and increased levels of mitochondrial DNA damage. These findings suggest that ongoing oxidative stress contribute to keratoconus.
Classification of keratoconus:-
Keratoconus can be classified by cone shape, central keratometric reading or progression.
The simplest classification systems are based on keratometric reading or shape.
Based on severity of curvature:-
Mild - < 45 D in both meridians
Moderate - 45 - 52 D in both meridians
Severe - 52 D in both meridians
Advanced - > 62 D in both meridians
Based on shape of the cone:-
Nipple small diameter(5 mm)
Oval Large diameter(> 5 mm)
Globus Large diameter (> 6 mm)
Signs, Symptoms and Diagnosis of Keratoconus:-
Sign:- Scissors reflex (swirling retinoscopy reflex) Distorted / irregular keratometer mires with steep reading Prominent corneal nerves
Symptoms:- Frequently changing spectacle Rx and axis of the Astigmatism.
* Poor repeatability of subjective refraction
* Ghosting / monocular diplopia Glare at night
* Haloes around lights Blurred / Distorted Vision
Computerized corneal topography techniques using curvature - based analysis and newer forms of elevation based tomography appear to be the most sensitive methods for detecting early keratoconus.
Prior to these, the most sensitive methods included Apical decentration on the keratometer
Subtle changing in the retinoscopic reflex that progress early scissoring and change the ablity to visualize the endothelial specular reflection relative to the epithelial reflection during slit-lamp biomicroscopy.
(The references are available upon request)