Topo Guided Lasik
Topoguided & Wavefront guided Lasik Treatment
In topography guided photoablation, corneal topography (point to point variation in curvature and refractive power) is used for photoablation in conjunction with the refractive error of the eye. Secondly, all measurements are centered on the corneal vertex and not on the pupillary center or geographical corneal center.
Different methods are used to evaluate the corneal topography, each with its own advantages and disadvantages. Either a placido-disc reflection of the anterior corneal surface or a Schiemflug-based imaging system can be used to obtain the topography maps.The placido-disc based device captures upto 22,000 true elevation points, including the posterior corneal surface.
The devices also digitally determine the limbus & pupillometry measurements using infrared camera. This helps in correctly identifying the pupil center intraoperatively & then shifting the ablation profile towards corneal vertex. All this pre-operative information transferred to excimer laser software. The software integrates refractive error & topography to generate an ablation profile. The profile can be mix of myopic and hyperopic ablation zones. It gives surgeon the option to choose optical zone as well as transitional in 0.1mm steps.
Complete refractive error or a part of it can be corrected based on pachymetry or surgeon’s preference. This strategy is useful in case of irregular corneas where smoothening of anterior corneal surface is a priority rather than correction of refractive error.
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In short, topoguided treatment offer a basket of choices.
- Smoothing of anterior corneal surface with or without correction of refractive error.
- Centering the ablation profile on the corneal vertex.
- Correction of asphericity and choosing the desired optical zone in smaller steps than conventional LASIK.
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What are specific indications?
- Post-LASIK Complications-Decentered ablation profile, small optic zone, button holes and vertical gas breakthrough with irregular flaps, post-LASIK ectasia.
- POST-RK cases
- Post-keratoplasty refractive error correction.
- Regularization of cornea in keratoconus (Combined with collagen cross linking)
A) Treatment of Regular Cornea
B) Treatment of Irregular Cornea
