Any optometrist will tell you that the keratometer has always been a useful instrument for helping them to understand the patient’s cornea; whether to measure corneal astigmatism, to assist in fitting of contact lenses, or to assess such corneal disorders as keratoconus. All practitioners can site examples where the reason for a patient’s poor vision did not become clear until keratometric measurements were considered.
However even the most sophisticated keratometers have limitations. In keratometry, only the central cornea is measured, only two meridians are analysed at a time and the instrument does not carry out any analysis of the data. While optometrists are able to assess the quality of keratometric mires, such assessment is subjective and difficult to describe in the clinical notes kept for each patient.
Thus it is no surprise that the corneal topographer is increasingly becoming a mainstream instrument in optometric practice. Topography allows the optometrist to truly analyse the cornea as never before and such analysis affords a profound increase in understanding of the cornea and its influence over a patient’s refraction and the quality of vision.
Shin Nippon has been a world leader in the development of the corneal topographer with its ground-breaking CT-1000. This instrument is of tremendous value in optometric practice, whether used purely as a screening instrument for irregular corneas, as an aid in refraction or in more sophisticated procedures such as orthokeratology. The instrument itself is extremely easy to use, as a result of its streamlined design and patented system of capturing and analysing the reflection from the cornea of its measurement cone, which consists of 20 rings and over six thousand measuring points … more than enough to accurately define any cornea. Unlike the keratometer, which reflects from only the central cornea, the CT-1000 measures almost the entire corneal surface, which gives a far truer picture of the cornea as a whole.
However it is the software that makes this corneal topographer an indispensable instrument in any consulting room. After taking a measurement, a graphical measurement of the patient’s cornea is sent to the PC and instantaneously appears on the monitor. The corneal profile can be demonstrated to the patient in 3D from different angular perspectives and the pupil and HVID are accurately measured.
The mathematical capability of the CT-1000 and its software are astounding. Not only are the corneal shape factors (“e”, “Q” and “p”) used in ortho-K automatically calculated for every cornea, but diagnosis of keratoconus is made easy by the KISA%, which categorises each patient as normal, suspect, early or advanced keratoconus.
Contact lens fitting is made extremely simple: corneal data can be printed and faxed or emailed to the contact lens laboratory of your choice. The software even simulates the fluorescein pattern and movement for a given lens design so that a “virtual fitting” can be viewed for any cornea that has been measured.
For optometrists that wish to use the CT-1000 for orthokeratology measurements, the software allows easy viewing and assessment of difference maps (both axial and tangential) and all maps can be viewed with either absolute or adjustable scales, to simplify identification of bulls-eyes, central islands or smiley faces.
The Shin Nippon CT-1000 has indeed become the 21st century standard in instrumentation for corneal assessment and analysis. Whether used in simple screening or complex fitting and diagnosis, this corneal topographer has effectively replaced the keratometer to become an essential part of any contemporary consulting room.
Lee Pepper
B. Optom (Hons)