97th DOG Annual Meeting 1999
AUTOMATED AND STANDARDIZED CALCULATION OF POTENTIAL CORNEAL CONTRAST SENSITIVITY BASED UPON VIDEO-TOPO-GRAPHY DATA
B. Wannke, E. Simader, M. Derse, T. Oltrup, T. Bende, B. Jean
The potential corneal contrast sensitivity (PCCS) is an important criterion of corneal optical quality. Determination of PCCS strongly depends on used variables (e.g. spatial frequency, object contrast). This may lead to misinterpretation of PCCS data if not all variables are considered correctly. A new procedure is introduced to avoid these problems and to obtain PCCS values standardized and automatically.
Methods: Videotopographic data was obtained using the Tuebinger color-coded videotopography system (C-Scan, Technomed). A new software module was developped which automatically calculates virtual retinal images from standardized objects with exactly defined sinusiodal luminance distrubution, spatial frequency and object contrast (ray-tracing). Selection of these objects was done according to clinical evaluation of contrast sensitivity data.
Results: The modulation transfer function (MTF) (=set of PCCS values for different spatial frequencies and object contrasts) can be determined According to the clinical situation, the MTF decreases with increasing spatial frequency and decreasing object contrast. Examples are given to correlate MTF with clinically determined contrast sensitivity pre- and post-PRK.
Conclusions: This new procedure allows an error-free comparison of PCCS and MTF intra- and interindividually. Due to automatization, the procedure is especially easy to use and to learn. The procedure permits a fast determination of PCCS and MTF in vivo and allows statements about the optical quality of the cornea and about the localization of a visual deficit. Based upon these data and clinical contrast sensitivity data further investigations of retinal and central signal processing become possible.
Univ. Eye Clinic, Dept. I, Schleichstr. 12, D - 72076 Tuebingen