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OCT provides insights into retinal changes after uneventful cataract surgery
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Even uneventful phacoemulsification significantly increases central macular thickness, as shown by an optical coherence tomography study.
“Why this postoperative thickening of the central retina is merely subclinical in some patients and leads to cystoid macular edema in others is not known. However, in both cases the underlying mechanism may be the same,” Surbhi Arora, MD, said.
The study aimed to evaluate the incidence of cystoid macular edema (CME) after uneventful phacoemulsification by means of OCT, to evaluate the procedure’s effect on central macular thickness (CMT) at various time points, and to assess the link between CMT changes and surgical and biometric parameters.
CME is the most frequent cause of unexpected decrease in vision after uncomplicated cataract surgery. It presents 4 to 6 weeks postoperatively in most cases but occasionally presents as early as 3 weeks or as late as 6 months postop. It occurs in 1% to 6% of patients after uncomplicated phaco.
“Although phacoemulsification has lowered the incidence of CME, the amount of inflammation and therefore the risk of CME increases with higher phaco power. Also, surgical complications dramatically increase the risk of CME. A ruptured posterior capsule is associated with 5% to 20% incidence, and retained lens fragments further increase the risk to 29%,” Arora said.
Fluorescein angiography can be used to confirm the diagnosis of CME, but it is an invasive procedure that can cause complications.
“OCT is considered as effective as angiography, but it is non-invasive and evidenced good reproducibility,” Arora said.
The study
In a prospective study of 100 eyes of 100 patients undergoing uneventful phaco, OCT was used to assess CMT changes and the presence of CME.
All patients underwent phacoemulsification by a single surgeon. A standard technique was used with a 2.8-mm clear corneal incision, 5- to 5.6-mm capsulorrhexis, hydrodissection, nucleus fragmentation using 40% ultrasound power, phaco chop technique and cortex aspiration. The IOLs were implanted in the bag, all viscoelastic was removed at the end of surgery, and antibiotic and steroid drops were administered for 6 weeks.
OCT scans were taken with dilated pupil preoperatively and during follow-up. Six radial line scans, 6 mm each in length, centered on the foveola were performed, and a topographical map of the macula was produced, from which the CMT values were taken.
“CMT was defined as the average thickness at the intersection of the six radial scans. CME was defined on OCT morphologically as appearance of cystoid spaces with intervening septae and abnormal foveal contour, with or without subretinal fluid in addition to a CMT value above normal limits for population,” Arora said.
Each patient’s fellow eye served as a control, and OCT measurements were taken preoperatively.
Results
CMT was found to increase at day 1 and then gradually decrease until at 2 months it reached a level slightly higher than the preop level. A positive statistically significant correlation was found between preop CMT and the CMT values at the various follow-up intervals. No correlation was found between preop or postop best corrected visual acuity and CMT value.
Only one patient developed CME, Arora said. This patient’s CMT increased from 178 µm preoperatively to 245 µm at 2 months — a 26.5% increase, compared to the average 4% increase in other eyes. The diagnosis of CME was confirmed on OCT by the morphological appearance of cystoid spaces with intervening septae and distorted foveal contour.
“CME presents a variable incidence in the literature. The 1% incidence in our study is in the lowest range,” Arora said. “However, we postulated that phaco, even when uncomplicated, may have an impact on the healthy retina. This could be attributed to factors such as intraoperative photostress due to the microscope light, intraoperative changes of the ocular pressure caused by surge or to the ultrasound energy delivered. Inflammation induced by the surgical trauma, with increased release of VEGF and interleukin-6, may be involved. Vitreous tractions following removal of the lens could also contribute.”
Arora also hypothesized that whatever causes the development of postop CME may also lead to a subclinical increase in central macular thickness and volume.
“What makes the response of some patients degenerate into pathology and become CME is yet unknown, and we need further studies,” she said.
OCT monitoring of the anatomical changes occurring in the retina after surgery could be a key factor in future studies. – by Michela Cimberle