ortho keratology

Views:
 
Category: Education
     
 

Presentation Description

No description available.

Comments

Presentation Transcript

Orthokeratology :

Orthokeratology Dr Raghu Nagaraju Cornea and Refractive Department Dr Agarwal’s eye hospital

PowerPoint Presentation:

Orthokeratology is the temporary reduction of myopia achieved by the programmed application of contact lenses to reshape the cornea

PowerPoint Presentation:

Contact lens wear is postulated to cause central corneal flattening accompanied by paracentral steepening, which results in a corneal shape factor that approaches zero (i.e., spherical). This process is accelerated by the use of reverse geometry lens designs which have a secondary curve that is steeper than the base curve to allow appropriate changes in the midperipheral cornea

PowerPoint Presentation:

Orthokeratology achieves this using specially designed reverse geometry gas permeable (GP) ortho -k shaping lenses worn during sleep. This overnight wearing process provides a faster, more predictable result George Jessen first attempted to deliberately change refractive myopic error using rigid contact lenses using a technique he named “ Orthofocus .”

PowerPoint Presentation:

Nick Stoyan , patented designs using reverse curve configurations (base curve flatter than the central cornea with a secondary curve of steeper radius) specifically for orthokeratology . Dr. Sami El Hage was the first to use topography to fit ortho -k lenses

PowerPoint Presentation:

Three major developments changed not only the process by which ortho -k shaping lenses were fit, but also how they are perceived. These are: 1. reverse geometry designs 2. the availability of high Dk GP lens materials 3. a better understanding of the relationship of these shaping lenses to the cornea through the use of corneal topography.

Concept :

Concept More spherical cornea and the lower the eccentricity, the smaller the ortho -k effect. corneas that had steeper corneal curves and higher eccentricities were believed to have a better chance of experiencing reduced myopia.

PowerPoint Presentation:

During this process, the cornea became more spherical (“ sphericalization ”) as the difference between the flatter and steeper corneal meridians became more similar and the eccentricity became lower. Corneas with flatter curves (36.00 to 39.00 diopters ) are thought to be more resistant to change, although this is an area that has recently come under debate.

Fitting steps:

Fitting steps The 3-curve reverse geometry design should be fitted 1.50 to 4.00 diopters flatter than the flattest corneal curvature (flatter than “K”). Lenses would exhibit 1.00 to 2.00 mm of movement with a blink. Centration is critical to success Patients were typically checked after four hours of lens wear to check for lens tightening and/or adhesion

PowerPoint Presentation:

24 years / F RE -2/ -1.5 X 100 0 LE -1.5 /-1.25X 25 0 Anterior segment and posterior segment was normal

Mechanism :

Mechanism ortho -k shaping lens fitting using reverse geometry GP designs may compress corneal tissue rather than changing refractive error by bending the cornea. The hypothesis is that a thin layer of tear film exists between the back of the ortho -k shaping lens and the central cornea. These tear film “shear” forces act hydraulically to force a compression and subsequent redistribution of very anterior epithelial cells under the lens from the center toward the periphery

Morphological :

Morphological The corneal epithelial cell layer is redistributed leading to a thinning of the central cornea to significant levels across the corneal surface. There was concurrent thickening of the mid-peripheral cornea, particularly in the stromal layer.

PowerPoint Presentation:

Tear film forces cause the apical epithelial cells to compress and possibly “migrate” toward the periphery. This corneal reshaping process creates a decrease in corneal sagittal height and causes the cornea to become more spherical and flatter, thereby reducing or eliminating the need for myopic correction

PowerPoint Presentation:

Modern four-zone ortho -k shaping lenses typically consist of: Base curve Reverse (steeper) curve Fitting (alignment) curve Peripheral curve

Gas permeability:

Gas permeability limiting corneal edema levels to 4% or less during sleep requires a lens capable of 87 Dk /t using soft contact lenses. This conclusion was based on using the transmissability formula x10 -9 (cm 2 /sec)(mlO2/ml x mmHg). It should also be taken into consideration that GPs cover a smaller area of the cornea and the Dk ratings are generally higher than with conventional soft contact lenses

Adverse effect :

Adverse effect The two most common side effects that occur in any rigid contact lenswearer are corneal edema and corneal staining extreme discomfort, redness, tearing, irritation, discharge, corneal abrasion or distortion of vision rare instances, there may occur permanent corneal scarring, decreased vision, and infections of the eye, corneal ulcer, iritis , or neovascularization

Conclusion :

Conclusion Overnight orthokeratology treatment is an interesting and exciting addition to today’s eye care practice. Patients who are interested in non-surgical vision correction and has reversible option . With today’s technology, proper candidates can be successful with this new and exciting treatment for myopia reduction.

authorStream Live Help