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

MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

in both eyes. The latent hyperopia OD was partially addressed, and the goal was a correction of +2.75 OD, +1.00 OS. She underwent bilateral femtosecond laser assisted keratomileusis using a VISX Star 4 laser.

S/P LASIK, the patient complained of blurred vison OD, and the UCVA dropped to 20/50. Manifest refraction found +1.50+1.25 x 180 while the cycloplegic again revealed the latent hyperopia: +3.00 + 1.25 × 180, yielding a VA of 20/30. Her visual complaint was relieved with simple hyperopic correction, and the patient underwent an enhancement by relift of +1.50 +1.25 x 180.

At one month, she presented complaining of decreased vision OD, multiple images, and “an unbalanced feeling”. Manifest refraction found –1.50+0.75 x 75, and corrected her to only 20/50. Her elevation maps reveal marked central steepening OD as seen on the elevation map in Figure 13a. Her wavefront aberrometry measurements revealed coma OD, shown in Figures 3.13B and C. Interestingly, the Wavescan and I-Trace both found hyperopic refractions. The coma suggested a decentered apex, and topography revealed a significant steepening just above the geographical center.

Neither correction of the manifest refraction with a soft lens nor Alphagan-P to change the pupil size corrected the patient’s complaint. While a gas perm lens did restore functional vision, the patient is not able to tolerate the lens.

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CHAPTER 3: CTWA: COMPLEMENTARY TOOLS

A

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

B

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CHAPTER 3: CTWA: COMPLEMENTARY TOOLS

C

FIGURES 3.13A TO C: (A) Elevation maps reveal marked central steepening OD S/P hyperopic lasik with hyperopic enhancement, as seen on the elevation map in Figure 3.13A. Her WaveScan map (B) and Itrace map (C) revealed coma, and reported hyperopic refractions despite a manifest of -1.50DS

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

It appears that the patient only uses the tip of the corneal for vision, resulting in the preferred myopia refraction. As time progressed and the naturally smoothing of the cornea occurrs, her symptoms are lessening, and we may perform a custom treatment in the future.

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4

CORNEAL ECTASIAIA POSTLASIK:I : THE ORBSCAN ADVANTAGE

• Erik L Mertens

• Arun C Gulani

• Paul Karpecki

MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

With the advent of corneal topography and its increasing application in practice, our knowledge about the shape of the cornea has rapidly accumulated. Determination of the ability of the cornea to undergo laser refractive surgery is of the utmost importance. The purpose is to avoid corneal ectasia and visual impairment in otherwise healthy eyes. First reported by Prof Theo Seiler this condition is characterized by progressive protuberance and steepening, increasing myopia and or astigmatism with distorted and decreased best corrected vision in the involved eye.

The decision to continue with refractive laser surgery is not based on a single clue, but rather on a combination of a set of criteria. When looking at the Orbscan’s Quad map you can find so called ‘red flags’ or ‘yellow flags’. A ‘red flag’ definitively means a no-go situation and a ‘yellow flag’ is suspicious and will drive our attention to look very closely into the other corneal maps. On a typical Quad map four corneal maps are routinely presented by the Orbscan II (Bausch and Lomb Orbtek, Salt Lake City, Utah). You will find the anterior elevation map in the upper left quadrant and the posterior elevation map in the upper right quadrant. The keratometric curvature map (power map) is located in the lower left quadrant and the pachymetry map in the lower right quadrant (Fig. 4.1). In the center of these four maps a lot of statistics and useful data are displayed.

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CHAPTER 4: CORNEAL ECTASIA POST-LASIK: THE ORBSCAN ADVANTAGE

FIGURE 4.1: Typical quad map (Orbscan II)

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MINI ATLAS SERIES: CORNEAL TOPOGRAPHY

An absolute contraindication for lamellar corneal laser surgery is a thinnest point of <470 microns. When pathological, this point is often displaced inferotemporal (Fig. 4.2). A difference of <30 microns (yellow flag) or <20 microns (red flag) between the central pachymetry and the peripheral thickness indicators can be seen in abnormal corneas (Fig. 4.3). A difference of > 100 microns from the thinnest point to the values at the 7 mm optical zone implies a steep gradient of thinning from the midperiphery towards the thinnest point (yellow flag) (Fig. 4.3).

POSTERIOR ELEVATION MAP (FIG. 4.4)

1.The most common reference surface for viewing elevation maps is the “best fit sphere” (BFS).

A posterior high point > 50 microns above BFS might be indicative of an early posterior ectasia. However in cylindrical corneas with an astigmatism >2.5 D this elevation can be induced by the astigmatism and needs to be checked with the other corneal maps (Fig. 4.5).

A posterior high point > 35 microns above BFS with corresponding thinning on the pachymetry map is a red flag for Lasik, but not for PRK, Lasek or epiLasik.

2.The power of the posterior best fit sphere (BFS) is in normal corneas around 51D. A BFS with a power of more than 55 diopters (Fig. 4.4) on the posterior profile,

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CHAPTER 4: CORNEAL ECTASIA POST-LASIK: THE ORBSCAN ADVANTAGE

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