Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard Mini Atlas Series CORNEALTOPOGRAPHY_Agarwal, Jacob_2009

MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

Bent/warped cornea. Similarly between anterior and posterior profiles implies a forward bending of those areas shown above the BFS. If these bending is in association with the thinnest point on the cornea. It could related to structural weakness in the cornea, irrespective of wheter the thinnest point still shows and adequated pachymetry. This sign has to be evaluated within the context of other signs above.

Inferotemporal displacement of the highest point: Inferotemporal displacement of the highest point on the anterior as well as the posterior elevation profile can be indicative of early keratoconus, but must also be seen in context (Fig. 5.10).

This is probably the strongest topographic sign indicative of early keratoconus. If the highest point on the posterior elevation coincides with the highest point of anterior elevation, the thinnest point on pachymetry, and the point of steepest curvature on the power map, one has to very careful regarding your decision to operate. This signs implies that the thinnest point represents an structural weakness, wich cause a forward bending of the cornea (as is noted on the posterior and anterior elevation maps), further supported by the curvature change on the power map (Fig. 5.11).

Recognizing keratoconus and the other forms of corneal pathology like pellucid marginal degeneration that contraindicate corneal laser refractive surgery is central to safe

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CHAPTER 5: ORBSCAN CORNEAL MAPPING IN REFRACTIVE SURGERY

clinical practice. As profesionals is our own responsibility to keep the prestige of refractive surgery and LASIK safe desicion must be our mision.

Finally, if some criteria of unhealthy cornea or posterior ectasia have been found, other refractive surgical techniques can be attempted such as phakic IOL in the case of fruste keratoconus or thin cornea for a high myopia patient (Fig. 5.12); or in the scenario of a keratoconus, intracorneal rings (Fig. 5.13) can be attempted, Orbscan

FIGURE 5.12: ICL Power calculator, Orbscan II can also help to obtain the data requiered to calculate ICL

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CHAPTER 5: ORBSCAN CORNEAL MAPPING IN REFRACTIVE SURGERY

offers us the posibility in helping to take this decision and follow-up.

REFERENCES

1.Maw R. Avoiding postoperative LASIK ectasia. Cataract and Refractive Surgery Today. Nov-Dec 2003.

2.Seiler T, Koufala K, Richter G. Iatrogenic keratectasia after laser in situ keratomileusis. J Cataract Refrac Surg 1998;14: 312-7.

3.Vaca, Oscar. Posterior float features in population screened for laser eye surgery. Mexican Cornea and Refractive Surgery Society 1999.

4.Ambrosio R, Klyce SD, Wilson SE. Corneal topographic and pachymetric screening of keratorefractive patients. J Refractive Surg 2003;19:24-9.

5.Ou RJ, Shaw EL, Glasgow BJ. Keratectasia after laser in situ keratomileusis (LASIK): evaluation of the calculated residual stromal bed thickness. Am J Ophthalmol 2002;134 (5):771-3.

6.Roush C. Orbscan II Manual (Salt Lake City, Utha. Orbtek).

7.Vukich J, et al. Early spatial changes in the posterior corneal surface after laser in situ keratomileusis. J Cataract Refract Surg 2003;29:778-84.

8.Potgeiter F. Custome Lasik Surgical Techniques and Complications. Buranto L, Brint S Slack 2004;435-7.

9.Assouline M. Chirugie Ceil–Le Kératocone. De nouveaux critéres de detection de kératocone infraclinique. www.inclo.com/le-keratocone.php

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

10.Fakhry M, Artola A, Belda J, Alio J. Comparison of corneal pachymetry using ultrasound and Orbscan II. J Cataract Refract Surg 2002;28:248-52.

11.Auffarth GU, Tetz MR, Biazid Y, Volcker HE. Keratoconus evaluation using the Orbscan Topography System. J Cataract Refract Surg 2002;26:222-8.

12.Lee DH, Seo S, Jeong KW, et al. Early spatial changes in the posterior corneal surface after laser in situ keratomileusis. J Cataracy Refract Surg 2003;29;778-84.

13.Twa MD, Roberts C, Mahmound AM, Chang JS Jr. Response of the posterior corneal surface to laser in situ keratomileusis for myopia. J Cataract Refract Surg 2003;31:61-71.

14.Miyata K,Tokunaga T, Nakahara M, et al. Residual bed thickness and corneal foward shifth after laser in situ Keratomileusis. J Cataract Refract Surg 2004;30:1067-72.

15.Grzybowski DM, Roberts CJ, Mahmound AM, Chang JS Jr. Model for nonectatic in posterior corneal elevation after ablative procedures. J Cataract Refract Surg 2005;31:72-81.

16.Cairns G McGhee NJ, Collins MJ, et al. Accuracy of Orbscan II slit scanning elevation topography. J Cataract Refract Surg 2002;28:2181-7.

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

INTRODUCTION

The combination of topographic and wavefront data is the foundation for customized ablation. The Zyoptix™ Diagnostic Workstation seamlessly integrates wavefront and topographical data for customized treatments. (Fig. 6.1) It is ergonomic and easy to use, and provides surgeons with a platform for comprehensive diagnosis and treatment. The ORBSCAN® IIz uses slit scanning

FIGURE 6.1: The Zyoptix™ Diagnostic Workstation

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CHAPTER 6: THE ORBSCAN IIZ DIAGNOSTIC SYSTEM AND SWAGE

technology to measure corneal curvature. It also provides true three-dimensional elevation based on triangulation and curvature of both anterior and posterior surfaces of the cornea. The ZYWAVE™ II ABERROMETER provides wavefront measurements based on Hartmann-Shack technology. It measures higher order aberrations (HOAs) up to the 5th order.

ORBSCAN

Corneal topography has evolved over time from a manual keratometer to simple placido disk topographers, to the Orbscan. The Orbscan uses a combination of placido disk images with 20 slit scans to the left and 20 slits scan to the right. This allows for forty overlapping scans in the central 5 mm zone that then allows for the four basic measurements listed below. The Orbscan measures four essential elements:

1.Corneal Power

2.Corneal Thickness

3.Anterior Corneal Elevation

4.Posterior Corneal Elevation

QUAD MAP

The quad map is the most common and useful way to get an overall view of the cornea. It combines anterior elevation,

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