The contrast sensitivity test in early detection of ocular changes in children, teenagers and young adults with diabetes mellitus type 1
Abstract
The authors examined repeatedly every year 213 patients (97 boys and young men and 116 girls and young women, age ranged 6-36 years, median: 16.4 years). The diabetes mellitus type I duration at the first eye examination was 0.1 to 26 years (median: 5.9 years), and was diagnosed at the age 2-30 years (median 10.5 years).
Changes of the posterior pole and their correlation to functional tests and to metabolic parameters were evaluated in five-years periods since the start of the study (within the fifth year of the study, between years 6-10, 11-15, and over 16 years of the study duration respectively). The beginning changes at the fundus were represented by means of dilatation of the capillaries with their possible obliteration and tortuosity, which was rare (7%) until the 5 th year of the disease duration, between 6-10 years it was almost in a half of the patients (43%), and after 10 years in was present in more than 90% of cases.
Changes of the macular structure by means of the irregularity of foveolar reflex and relative retinal thickening without significant macular edema with increased pigmentation of this region appeared rarely after the fifth year (5%) and after 15 th year of duration were present in more than two thirds of eyes (65%). Combination of these two findings was considered as diabetic preretinopathy (DpR), and was detected in 9% of eyes until 10 years of duration of diabetes.
The number of hard exudates and microaneurysms gradually increased. Signs of non-prolipherative diabetic retinopathy were noticed in 0.5% of cases by means of ophthalmoscopical examination in patients with duration of diabetes type I less than 10 years.
After that period, the non-prolipherative diabetic retinopathy was present in 19% of cases, and diabetic preretinopathy in 42%. The contrast sensitivity was examined by means of CSV-1000 instrument in 3, 6, 12 and 18 cycles/degree (c/deg) respectively.
Normal values for children 6 years old and older were established in a previous study in a control group of children and teenagers without diabetes and with healthy eyes. In the age range 6-10 years the mean threshold values [log] are for: 3 c/deg 1.82; 6 c/deg 2.04; 12 c/deg 1.74; and 18 c/deg 1.29.
Since the age of 11 years, normal mean threshold contrast sensitivity values [log] are for: 3 c/deg 1.92; 6 c/deg2.19; 12 c/deg 1.89; and 18 c/deg 1.42. No statistically significant difference was found in respective frequencies at the contrast sensitivity curve formulation.
The marginal contrast level with standard deviation less than 0.15 log (range, 0.09 -0.14), for all spatial frequencies represents for children aged 6-10 years the 5 th stimulation target, and for those of 11 years of age and older the 6 th stimulation target disc of the instrument. The value of pathologically decreased contrast sensitivity increased depending on the duration of the diabetes from 1.5% (up to 5 years of diabetes) to 23% after 15 years of diabetes.
The lowest decrease of contrast sensitivity in pathological and border values of space frequencies was found in low-frequency 3 c/deg, which shows the evidence of perifoveolar involvement. No statistical significant difference was found among particular frequencies of low, middle, and higher contrast levels in pathological values of contrast sensitivity, but in case of counting in their border values, the statistical significant difference (p = 0.036) was established between the two frequencies 3 c/deg and 18 c/deg, which is giving the evidence of perifoveolar rather than exactly foveolar changes in scope of diabetes mellitus type I.
The total decrease of contrast sensitivity values was determined by the increase of changes' number at the posterior pole by means of diabetic preretinopathy and non-prolipherative diabetic retinopathy mostly after 10 years of diabetes duration. Lowering of the contrast sensitivity by 65% is directly related to already mentioned changes of the macular region structure (MDM) and involvement of the foveola with preserved visual acuity.
The decrease of the contrast sensitivity corresponded mostly with the posterior pole finding, and not with the diabetes duration, especially in middle and higher frequencies of 6, 12, and 18 c/deg. Changes in color vision by means of 15 Hue test were found in 7% of followed patients and those were not in direct connection with the disease, but were similar to changes in normal population.
The decrease of contrast sensitivity values did not depend on the actual metabolic status of the basic disease (actual blood sugar and Hb A1c levels at the time of the ocular examination), nor with the one year level of compensation of diabetes (level of Hb A1c and microalbuminuria during the one year of the study. Conclusion: The contrast sensitivity examination by means of CSV-1000 device was not time consuming, non invasive for the patients and in case of good cooperation revealed the functional insufficiency of the retina, which was the sign of initial diabetic changes in foveolar and perifoveolar region structure.