Effect of Spectral Domain Optical Coherence Tomography Image Quality on Macular Thickness Measurements and Error Rate.

PURPOSE: To evaluate the effect of Topcon spectral domain optical coherence tomography (OCT) image quality on macular thickness measurements and the error rate in healthy subjects and patients with clinically significant diabetic macular edema (CSME). METHODS: In this prospective, comparative case series, macular thickness measurements, and the rate of decentration and segmentation errors were evaluated before and after reducing the image quality factor (QF). The measurements were evaluated again after correcting the decentration and segmentation errors. To reduce the image QF below 45, tetracycline eye ointment was applied on the corneal surface. RESULTS: Forty eyes of 40 subjects including 18 healthy eyes and 22 eyes with CSME were included. In both groups, the difference in central subfield thickness measurements before and after reducing the image QF was not statistically significant both before and after error correction (all P>0.05). The rate of decentration error was statistically similar before and after reducing image QF in normal and CSME eyes (P=0.50, P=0.69, respectively). However, the rate of segmentation error was statistically significantly higher after reducing image QF both in normal and CSME eyes (P=0.008 and P=0.004, respectively). In both groups, eyes with a segmentation error had higher image QF reduction (both P=0.01). CONCLUSION: Reducing image quality results in a higher rate of the segmentation error in normal eyes and in eyes with CSME.

Macular thickness measurement in clinically significant macular edema before and after meal.

PURPOSE: To evaluate the macular thickness changes in diabetic macular edema after meal. METHODS: In this prospective case series, macular thicknesses of diabetic patients with clinically significant macular edema (CSME) were measured after 7 h of fasting and repeated 2 h after breakfast. RESULTS: Thirty six eyes of 20 diabetic patients were evaluated. The mean central subfield thickness (CST) and maximum retinal thickness (MRT) significantly decreased after meal (mean change of -10.3 ± 14.3 µm and -13.1 ± 12.7 µm, respectively, both P < 0.001). A decrease in CST and MRT values was found in 23 (63.8%) and 28 (77.7%) eyes, respectively, and no eye had an increase in retinal thickness measurements. Significant correlation was found between CST and MRT change and fasting thickness measurements (P = 0.001 and P = 0.01, respectively) and intraretinal cystic spaces (P = 0.001 and P = 0.03, respectively). Mean MRT change was significantly higher in the presence of subretinal fluid (P = 0.01). CONCLUSION: Retinal thickness measurements may change after meal. So, fasting state of diabetic patient should be considered in measurement of macular thickness of patients with CSME.

Effect of grid decentration on macular thickness measurements in normal subjects and patients with diabetic macular edema.

PURPOSE: To evaluate the effect of optical coherence tomography (OCT) grid decentration on macular thickness measurements in healthy subjects and patients with diabetic macular edema. METHODS: In this prospective study, 3D spectral-domain OCT images of 51 eyes with clinically significant diabetic macular edema and 29 healthy eyes were assessed. In each eye, the macular Early Treatment Diabetic Retinopathy Study grid was evaluated for decentration. After grid adjustment, changes in central subfield thickness (CST) and central subfield volume (CSV) measurements were recorded. Changes >1 µm and >8.5 µm in CST were considered as grid decentration and clinically significant grid decentration, respectively. RESULTS: Grid decentration was found in 10 normal eyes (34.6%) and 32 clinically significant macular edema (CSME) eyes (62.7%, p = 0.01). Clinically significant CST changes were found in 3 normal eyes (10.3%) and 23 CSME eyes (45%, p = 0.001). The mean change in CST after grid adjustment was 6.4 ± 5.8 µm and 24.7 ± 27 µm in normal and CSME eyes (p = 0.04). Age, sex, and CST had no statistically significant effect on grid decentration in normal and CSME eyes. Best-corrected visual acuity was significantly worse in eyes with grid decentration (0.75 ± 0.55 vs 0.42 ± 0.22 logMAR, p = 0.02) and clinically significant grid decentration (0.81 ± 0.6 vs 0.45 ± 0.27 logMAR, p = 0.01). Change in CSV was detected in 3 normal eyes (10.3%) and 24 CSME eyes (47%, p = 0.001). CONCLUSIONS: Grid decentration occurs in a large number of OCT thickness maps and leads to significant error in macular thickness measurements. The effect is more prominent in patients with CSME.