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Custom Ablation for Irregular Astigmatism

www.crstodayeurope.com

We studied highly irregular corneas to address the special requirements of treating complex cases with irregular astigmatism.

By Aleksandar Stojanovic, MD

Excerpt: Consistent technological and surgical skill improvements have led to excellent outcomes and very low enhancement rates in modern laser refractive surgery. Consequently, most surgeons’ refractive experience is limited to treatments in mainly uncomplicated virgin cases. Unfortunately, when we apply the same reasoning and technology to complex secondary cases with irregular astigmatism, results become more inconsistent, and cases may even deteriorate.

There could be several reasons why the common technology and techniques that work so well on virgin eyes do not work as well in the treatment of irregular astigmatism. First, the most current diagnostic equipment for custom data acquisition is often not capable of detecting all the necessary features of an irregular cornea, since it is fine-tuned to detect details in virgin eyes. Second, the software’s ablation-planning strategy assumes optimization of intact preoperative optics and not a restoration of distorted optics. Finally, surgical techniques and equipment are for treatment of virgin eyes.

In an ongoing study at the University Hospital of North Norway, in Tromsø, we attempted to circumvent the above-mentioned obstacles and address the special requirements that we thought were necessary to treat complex cases with irregular astigmatism. First, we found the optimal method of registering relevant preoperative information in eyes with irregular astigmatism. After a decentration of corneal optics, the eye attempts to compensate for the visual distortion and rotates into a new fixating position. This results in a change of corneal intercept and inclination of fixation axis (Figures 1 and 2). Consequently, a map of a fixating eye with decentered optics, acquired by monocular placido topography and/or aberrometry, would give us a reference to the eye position, as previously described. It would also constrain our treatment options to optimization of the corneal/eye optics reflecting that position and possibly lead to unnecessary corneal tissue consumption.1 Therefore, we based our custom data on corneal morphology (ie, altimetry data), mapped independently of the rotational position of a fixating eye. For that purpose, we used elevation topography maps (calculated by triangulation) instead of wavefront aberrometry or monocular placido-based topography that provides a single shot of the eye/corneal optics bound to the line of sight or fixation axis, respectively.

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Moose's comments - this article appears to be in direct contrast to another article that Moose just posted. Progress should be noted but there certainly have not been enough case studies or publications to encourage anyone to seek re-treatment.
 
Posts: 1337 | Registered: Sun April 29 2001Reply With QuoteEdit or Delete MessageReport This Post
StarEyed
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quote:
In an ongoing study at the University Hospital of North Norway, in Tromsø, we attempted to circumvent the above-mentioned obstacles and address the special requirements that we thought were necessary to treat complex cases with irregular astigmatism. First, we found the optimal method of registering relevant preoperative information in eyes with irregular astigmatism. After a decentration of corneal optics, the eye attempts to compensate for the visual distortion and rotates into a new fixating position. This results in a change of corneal intercept and inclination of fixation axis (Figures 1 and 2).


Seems to make sense.
 
Posts: 104 | Registered: Fri November 05 1999Reply With QuoteEdit or Delete MessageReport This Post
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