Corneal Topography - Development

Development

The corneal topograph owes its heritage to 1880, when the Portuguese ophthalmologist Antonio Placido viewed a painted disk (Placido's disk) of alternating black and white rings reflected in the cornea. The rings showed as contour lines projected on the corneal tear film. Javal L., an pioneer in the field in the 1880's incorporated the rings in his opthalmometer and mounted an eyepice which magnified the image of the eye. He proposed that the image should be photographed or diagrammatically represented to allow analysis of the image.

In 1896, Allvar Gullstrand incorporated the disk in his ophthalmoscope, examining photographs of the cornea via a microscope and was able to manually calculate the curvature by means of a numerical algorithm. Gullstrand recognized the potential of the technique and commented that despite its laboriousness it could "give a resultant accuracy that previously could not be obtained in any other way". The flat field of Placido's disk reduced the accuracy close to the corneal periphery and in the 1950s the Wesley-Jessen company made use of a curved bowl to reduce the field defects. The curvature of the cornea could be determined from comparison of photographs of the rings against standardized images.

In the 1980s, photographs of the projected images became hand-digitized and then analysed by computer. Automation of the process soon followed with the image captured by a digital camera and passed directly to a computer. In the 1990s, systems became commercially available from a number of suppliers. The first completely automatic system was the Corneal Modeling System (CMS-1) developed by Computed Anatomy, Inc. in New York City, under the direction of Martin Gersten and a group of surgeons at the New York Eye and Ear Infirmary. The price of the early instruments was initially very high ($75,000), largely confining their use to research establishments. However, prices have fallen substantially over time, bringing corneal topographs into the budget of smaller clinics and increasing the number of patients that can be examined.