A Novel Technique For An Unbiased Evaluation Of Visual Results After Surgical Treatment Of Ectatic Corneal Diseases For Visual Rehabilitation

The purpose of the study is to present the Performance Plot Analysis (PPA)  as a novel data analysis technique which allows an unbiased comparison of surgical results of the treatment of ectatic corneal diseases. The problem of the currently available data analysis techniques for the evaluation of visual results after the surgical treatment of ectatic corneal diseases for visual rehabllitation depend strongly on the composition of the treatment groups. Without PPA a composition of advanced cases usually gives different results for the visiual improvement compared to groups consisting of milder cases and an unbiased comparison of different settings and different treatment groups is therefore currently not possible.

Keratoconus Treatment Center and University Hospital, Austria

502 eyes ectatic eyes were treated by Intra Corneal Complete Ring (ICCR) implantation and were analysed by the PPA technique. The preoperative and postoperative visual and refractive data include uncorrected distance visual acuity (UDVA) in logMAR, corrected distance visual acuity (CDVA) in logMAR, UDVA line improvement, CDVA line improvement, sphere, cylinder, axis and spherical equivalent (SE), respectively. The preoperative data were arranged according to the severity of the disease and related to the postoperative data by a regression analysis compared against a hypothetical 20/20 vision improvement. PPA provides the geometric mean of the visual and refractive data plane and the linear regression parameters as success indicators.

PPA provides non only a numerical but also a graphical representation of the treatment results across the entire severity spectrum related to the treated eyes. Extracted PPA values are regression intercept for UDVA line improvement of -2.0 lines and for CDVA line improvement of -0.19, repectively. The success line slopes are 8.7 and 8.0 for UDVA and CDVA line improvement, respectively. These values indicate a uniform effectivity across the entire severity spectrum from mild to advanced cases. The geometric mean of the refractive results are (-3.4, +0.48) for the sphere, (-2.73, -1.55) for the cylinder and (-4.77, -0.29) for SE, respectively. These data will be discussed and explained also in their graphical representations.

PPA is an excellent tool for the unbiased evaluation of visual and refractive results of surgical treatments for visual rehabilitation in ectatic corneal diseases. It allows a unbiased comparison of different surgical techniques and different settings. It is also an excellent tool for the surgical education and training and allows the measurement of the training progress of individual surgeons.