Korean J Ophthalmol.  2006 Mar;20(1):13-17. 10.3341/kjo.2006.20.1.13.

Anterior Elevation Maps as the Screening Test for the Ablation Power of Previous Myopic Refractive Surgery

• Jeong SY
• Chin HS
• Oh JH

• KMID: 1099067
• DOI: http://doi.org/10.3341/kjo.2006.20.1.13

Abstract

PURPOSE: We classified the Orbscan anterior elevation maps in normal eyes (under myopic, emmetropic and hyperopic conditions) and in those after myopic refractive surgery. We did this classification to demonstrate how Orbscan anterior elevation maps are useful in screening for the existence and extent of previous myopic refractive surgery. Such a classification can help clinicians interpret preoperative and postoperative topographies. METHODS: We measured for visual acuity and refractive power in 4800 eyes. After a slit-lamp examination, a corneal topography exam was performed with an Orbscan corneal topography system. The eyes were divided into two groups, with Group I representing those who had not had refractive surgery (4438 eyes). Group II included those who had undergone previous refractive surgery to correct myopia (362 eyes). RESULTS: In Group I, the central island type (43.0%) was the most common, followed by the temporal ridge (25.8%), the with-the-rule regular ridge (16.7%), the against-the-rule regular ridge (6.6%), the nasal ridge (4.0%), and the saddle type (2.1%). In Group II, the depressed lake type (69.9%) was most common, followed by the de-centered ablation type (21.3%). The trend line of the postoperative central anterior surface elevation (E) and the ablation power of refractive surgery were calculated. Ablation power of refractive surgery=0.0047 E+0.0083 CONCLUSIONS: This study demonstrates that it is possible to use Orbscan anterior elevation maps to screen for the extent of previous refractory surgery used in the correction of myopia. This study may also be useful in understanding the shapes of Orbscan anterior elevation maps before and after myopic refractive surgery as well as in determining the degree of ablated myopic refractive power and decentration.

Keyword

Anterior elevation map; Orbscan; Refractive surgery

MeSH Terms

Vision Screening/*instrumentation
Retrospective Studies
Preoperative Care
Postoperative Period
Myopia/*diagnosis/surgery
*Keratomileusis, Laser In Situ
Humans
Equipment Design
*Corneal Topography
Cornea/*pathology
Adult

Figure

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  Fig. 1 Anterior elevation map of the Orbscan corneal topography system.

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  Fig. 2 Orbscan IIz corneal topography system. (Bausch & Lomb, USA)

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  Fig. 3 Trend line about the 0.5mm radius central anterior surface elevation (E) and ablation power of refractive surgery.

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  Fig. 4 Anterior elevation map of the Orbscan corneal topography system before refractive surgery.

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  Fig. 5 Anterior elevation map of the Orbscan corneal topography system after myopic refractive surgery.

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