Journal of Refractive Surgery

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Book Reviews 

Corneal Topography: Measuring and Modifying the Cornea

David Miller, MD

Abstract

Corneal Topography: Measuring and Modifying the Cornea by D.J. Schanzlin and J.B. Pobin. New York, NY: Springer- Verlag Publishers; 1991. 185 pages. $98.00.

Measuring the power and shape of the human cornea has a long and rich history. In 1619, Father Christoph Scheiner compared the reflection from his subject's cornea to those from a calibrated series of glass balls. One might see this as the start of ophthalmometry. In 1880, Antonio Placido, a Portuguese ophthalmologist, introduced us to qualitative keratoscopy with his large target of concentric rings. This method revealed information about the corneal topography beyond the central 2 to 3 mm. Alvar Gullstrand, the ophthalmologist/future Nobel Laureate introduced the first step in quantification of topography by photographing the Placido disk reflections of the cornea. By 1922, Engellet quantitated the various corneal zones from topographic photos. The cornea was introduced to the computer in the 1980s. In 1981, Doss, Hutzon, and Rowsey used a computer to quantify the keratoscopic picture by concentric circles of numbers and in 1984, Steve Klyce converted the computer-generated information into a user-friendly color map of the corneal topography.

Table

As of early 1992, some 500 sophisticated topography devices have been sold to eye clinicians, which give quantitative color maps of the corneal topography. How is this information used by the clinician? Such maps help fitters design contact lenses for irregularly-shaped corneas. Corneal maps also direct the surgeon to the tight suture or the best location to place a relaxing incision in postoperative astigmatism. By contouring the entire cornea, these maps can accurately follow the progress of keratoconus much more accurately than conventional keratometry. Above all, it is the intuitive hope of the surgeon that such maps will help make future refractive surgery more predictable.

Is this book effective in teaching the reader how these devices work, and how they may be applied to clinical situations? There are three chapters by Klyce et al, El Hage, and Cohen which review the mathematical optics of computerized videokeratography. Although well conceived and written by true experts, these chapters will be a bit difficult for the nonmathematically-oriented reader. There are some strong chapters on terminology and comparison of instruments. These are followed by practical chapters on the progress of keratoconus using contour maps, contact lens fitting techniques using maps, the postoperative appearance of radial keratotomized corneas using striking colored maps as examples, and the latest philosophy in surgically-correcting astigmatism. From a pictorial point of view, the book features a number of examples of colored corneal contour maps, as weil as Placido disk patterns depicting many clinical situations.

As with any multiauthored book, there is a bumpiness of style and readability. For example, I'm still not sure what the author meant when he wrote, "It is an axiom that loss of peripheral corneal stroma results in flattening to the tangent of the thinned area." As far as the claims made for specific topography devices, made by specific companies, the reader has to be very careful in assessing some of the assumptions of the chapters concerned with these specific machines. Overall, the book effectively satisfies a niche created for those who want to know about this new/old area of corneal topography.

REVIEW SCORECARD…

Corneal Topography: Measuring and Modifying the Cornea by D.J. Schanzlin and J.B. Pobin. New York, NY: Springer- Verlag Publishers; 1991. 185 pages. $98.00.

Measuring the power and shape of the human cornea has a long and rich history. In 1619, Father Christoph Scheiner compared the reflection from his subject's cornea to those from a calibrated series of glass balls. One might see this as the start of ophthalmometry. In 1880, Antonio Placido, a Portuguese ophthalmologist, introduced us to qualitative keratoscopy with his large target of concentric rings. This method revealed information about the corneal topography beyond the central 2 to 3 mm. Alvar Gullstrand, the ophthalmologist/future Nobel Laureate introduced the first step in quantification of topography by photographing the Placido disk reflections of the cornea. By 1922, Engellet quantitated the various corneal zones from topographic photos. The cornea was introduced to the computer in the 1980s. In 1981, Doss, Hutzon, and Rowsey used a computer to quantify the keratoscopic picture by concentric circles of numbers and in 1984, Steve Klyce converted the computer-generated information into a user-friendly color map of the corneal topography.

Table

REVIEW SCORECARD

REVIEW SCORECARD

As of early 1992, some 500 sophisticated topography devices have been sold to eye clinicians, which give quantitative color maps of the corneal topography. How is this information used by the clinician? Such maps help fitters design contact lenses for irregularly-shaped corneas. Corneal maps also direct the surgeon to the tight suture or the best location to place a relaxing incision in postoperative astigmatism. By contouring the entire cornea, these maps can accurately follow the progress of keratoconus much more accurately than conventional keratometry. Above all, it is the intuitive hope of the surgeon that such maps will help make future refractive surgery more predictable.

Is this book effective in teaching the reader how these devices work, and how they may be applied to clinical situations? There are three chapters by Klyce et al, El Hage, and Cohen which review the mathematical optics of computerized videokeratography. Although well conceived and written by true experts, these chapters will be a bit difficult for the nonmathematically-oriented reader. There are some strong chapters on terminology and comparison of instruments. These are followed by practical chapters on the progress of keratoconus using contour maps, contact lens fitting techniques using maps, the postoperative appearance of radial keratotomized corneas using striking colored maps as examples, and the latest philosophy in surgically-correcting astigmatism. From a pictorial point of view, the book features a number of examples of colored corneal contour maps, as weil as Placido disk patterns depicting many clinical situations.

As with any multiauthored book, there is a bumpiness of style and readability. For example, I'm still not sure what the author meant when he wrote, "It is an axiom that loss of peripheral corneal stroma results in flattening to the tangent of the thinned area." As far as the claims made for specific topography devices, made by specific companies, the reader has to be very careful in assessing some of the assumptions of the chapters concerned with these specific machines. Overall, the book effectively satisfies a niche created for those who want to know about this new/old area of corneal topography.

REVIEW SCORECARD

10.3928/1081-597X-19920701-18

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