Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009

x / LASIK

The authors have put together the standard images that are needed for the preoperative assessment, management of the patient with the newest wavefront and femtosecond technology, and also for the management of complications of LASIK.

Continue to grow your knowledge and awareness of refractive surgery by putting this work to use in your practice. You will be thankful that you did. As a surgeon and clinician, keep advancing the field of refractive surgery.

David R Hardten MD

Minneapolis, MN

2 / LASIK

Figure 1.1: Illustration demonstrating LASIK.

Note the flap created

The combination of Ignacio Barraquer work and the introduction of the excimer lasers lead to a new surgical technique. Ioannis Pallikaris, MD coined the term LASIK (laser-assisted in situ keratomileusis), and was the first to create a “flap” of tissue with the microkeratome, rather than remove the entire top layer (Figure 1.1). He conducted the first animal trials of what is now modern LASIK in the late 1980s in his native Greece. Today LASIK is the dominant corneal refractive technique used to correct ammetropias around the world. Improvements in the creation of the corneal flap continue with improved

4 / LASIK

Figure 1.2: General quad map of a normal eye as seen on the Orbscan

Keratometry and corneal topography with placido disks systems were originally invented to measure anterior corneal curvature. Computer analysis of the more complete data acquired by the latter has in recent years has been increasingly more valuable in the practice of refractive surgery. The problem in the placido disk systems is that one cannot perform a slit scan topography of the cornea. This has been solved by an instrument called the Orbscan that combines both slit scan and placido images

6 / LASIK

To summarize:

1.Curvature is not relevant in raytrace optics.

2.Elevation is complete and can be used to derive surface curvature and slope.

3.Elevation is the standard measure of surface shape.

4.Elevation is easy to understand.

The problem we face is that there is a cost in converting

elevation to curvature (or slope) and vice versa. To go from elevation to curvature requires mathematical differentiation, which accentuates the high spatial frequency components of the elevation function. As a result, random measurement error or noise in an elevation measurement is significantly multiplied in the curvature result. The inverse operation, mathematical integration used to convert curvature to elevation, accentuates lowfrequency error. The Orbscan helps in good mathematical integration. This makes it easy for the ophthalmologist to understand as the machine does all the conversion.

The general quad map in the Orbscan of a normal eye (Figure 1.2) shows four pictures. The upper left is the anterior float, which is the topography of the anterior surface of the cornea. The upper right shows the posterior float, which is the topography of the posterior surface of the cornea. The lower left map shows the keratometric