Valid parameters for investigation of the pupillary light reflex in normal and diabetic subjects shown by factor analysis and partial correlation

Summary Pupillary test data of 103 normal and 119 diabetic subjects (47 IDDM, 72 NIDDM) were evaluated by factor analysis. From a total of nine pupillary parameters three factors were extracted in the analysis. Factor 1 represents maximal pupillary area, contraction velocity at 1 s, dilation velocity at 6 s and minimal pupillary area — static and simple dynamic parameters; factor 2 amplitude of pupillary unrest, area under the detrended curve of pupillary unrest and period of pupillary unrest — parameters of pupillary unrest; factor 3 fusion frequency of pupillary response following flicker stimuli and latency time of pupillary light reflex — second order dynamic parameters. Factor analysis was then applied to investigate diabetic patients with a high percentage of autonomic neuropathic participants (about 39 % had pupillary and about 35 % had cardio-respiratory function disorders), which revealed the same three factors as those identified in normal subjects. Furthermore, an age-related database of parameters of pupillary unrest is given. It demonstrates that normal subjects and diabetic patients did not differ in the period of pupillary unrest (normal vs diabetic (mean±SEM): 1550±29 vs 1536±27 ms; 2p>0.5). The difference in amplitude (47.8±2.8 vs 41.0±2.6 % percentile; 2p=0.071) and area under the detrended curve of pupillary unrest (47.9±2.8 vs 40.8±2.6 % percentile, 2p=0.062) seems to show a trend but was not significant. In conclusion, factor analysis revealed three different pupillary test factors. From the comparison of normal and diabetic subjects factor 1 which accounts for the highest percentage of variance (43 %) and factor 3(12 %) appear to be useful for investigating the pupillary light reflex. Factor 2 is not useful because of the insignificant differences between the normal and diabetic group. From factor analysis and partial correlation we believe that pupillary autonomic function in diabetic patients can be best assessed by using only two parameters, maximal pupillary area and latency time.Abbreviations IDDM Insulin-dependent diabetes mellitus - NIDDM non-insulin-dependent diabetes mellitus - lx lux - lm lumen