الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 90 |  |  |
| | | from | 90 | | |
Abstract
Keratoconus is a progressive, bilateral but typically asymmetric, non-inflammatory ectasia of the cornea. The disease is highly variable in its course. Classically, keratoconus has its onset at puberty and is progressive for 10–15 years. This degenerative disorder is characterized by central corneal stromal thinning, apical protrusion, irregular astigmatism, and variable degree of scarring. The thinner apex becomes downwardly displaced giving rise to irregular astigmatism, a hallmark of the disorder, which results in mild to marked impairment in the quality of vision. Most keratoconic patients (74% of eyes) can be managed non-surgically, while the remaining (26%) are managed with keratoplasty.
Fitting of RGP lenses for keratoconus patients can be challenging, involving the trial of many diagnostic contact lenses before a suitable final lens can be prescribed to the patient. The use of corneal topography for diagnosis of keratoconus is quite common but, its use in actually determining the contact lens parameters such as the back optic zone diameter (BOZD) and lens diameter (LD) and how they relate to the shape and size of the cone has been under-utilized.
The purpose of this study was to examine the relationship between cone diameter, steepest K readings derived from corneal topography and the BOZD and LD of the contact lens fitted. The study included 40 eyes suffering from keratoconus. Keratoconus was diagnosed based on clinical findings and topographic findings. Patients who had a history of other ocular co-morbidity, amblyopia, or previous surgery or trauma were excluded.
All patients underwent complete ophthalmologic examination and corneal topography analysis. The tangential radius maps were used to define the exact size and location of the cone. The cones were subdivided into two categories: Nipple cones and oval cones
To measure the size of the cone, a screen caliper was placed over the topographic map and the horizontal diameter of the cone was measured to one tenth of a centimeter. Two measurements were obtained: the cone peak diameter and the overall cone diameter. The parameters of the lenses such as base curve, back optic zone diameter (BOZD) and lens diameter (LD) were recorded. The diameter of nipple and oval cones were measured and related to the steepest K readings and to the lens parameters.