By Michael G. Haas, MD
This prospective study found that cataract removal increases retinal nerve fiber layer (RNFL) and macular thickness and improves spectral domain OCT repeatability, especially with Cirrus OCT.
The study included 60 eyes of 60 healthy subjects who underwent Cirrus and Spectralis OCT scans one month before and one month after cataract surgery.
Both devices detected significant increases in RNFL thickness after surgery. With Cirrus OCT statistical differences were observed in mean thickness and superior and temporal quadrants (P < 0.05), with the greatest difference being in the superior quadrant (5 µm higher after surgery, P = 0.026). With Spectralis OCT the superior, inferotemporal, temporal and superotemporal RNFL sectors were significantly thicker after surgery (P < 0.05), with the greatest difference being in the inferotemporal sector (10 µm thicker after surgery, P = 0.029).
All macular parameters were significantly increased after surgery with Cirrus OCT, with the largest difference being in foveal thickness (60 µm higher after surgery, P = 0.006). With Spectralis OCT, macular thickness measurements were not significantly different after surgery.
Both the Cirrus and Spectralis SD-OCTs had better repeatability after cataract removal. Cirrus RNFL measurements were highly reproducible after surgery for all quadrants and sectors: The mean coefficient of variation (COV) was 7.92 percent before surgery and 2.15 percent after surgery (P = 0.005). Spectralis OCT had better repeatability after surgery, but COVs were not significantly different before and after surgery.
The authors note that the clinical implication of these results is important because the measurements obtained with an OCT in patients with cataract should be interpreted cautiously, as the changes observed in macular or RNFL thicknesses may be caused by the variability associated with the presence of cataract and not by an actual change in the patient’s pathology.
Furthermore, these results show that there are some parameters whose variability improved more than others after cataract extraction: The repeatability of the mean and temporal quadrant thicknesses using a Cirrus OCT showed a statistically significant improvement after surgery. They write that in the case of measurement discrepancies, the most reliable postoperative parameters for the ophthalmologist (because they were the least variable) are the RNFL mean thickness and macular superior inner area thickness with both devices.
They conclude that cataracts influence OCT measurements and this should be taken into account when interpreting OCT scans in elderly patients. However, even in the presence of cataract, the OCT scans of individual patients remain reliable for clinical interpretation of gross retinal pathology, although RNFL and macular thickness values may be lower due to the presence of the cataract.