OCT reveals that macular thickness decreases after epiretinal membrane surgery

Improvement in VA still possible, despite a continuing abnormal macular profile.

Issue: March 1, 2001

ByBob Kronemyer

PARIS — Although macular thickness significantly decreases following epiretinal membrane surgery in most instances, the macular profile rarely returns to normal. Still, an abnormal macula after surgery does not preclude a satisfactory improvement in visual acuity, according to a study that evaluated the preoperative and postoperative aspects of epiretinal membrane using optical coherence tomography.

“Optical coherence tomography (OCT) allows precise pre- and postoperative evaluation of macular thickening and precise evaluation of the vitreomacular relationship,” said first author Pascale G. Massin, MD, an associate professor of ophthalmology at the University of Paris.

“This technology also demonstrates that macular thickening is an important component of the macular damage caused by epiretinal membrane constriction,” Dr. Massin said.

The noncomparative, interventional series consisted of 62 eyes of 62 consecutive patients operated on for an idiopathic epiretinal membrane. The mean age of patients was 67 years (range 46 to 80 years), with a mean duration in visual symptoms (visual loss and/or metamorphopsis) of 22 months (range 3 to 120 months). Overall, 51 eyes were phakic and 11 were pseudophakic, with posterior chamber IOLs.

Extensive exam

“Surgery consisted of standard three-port, pars plana vitrectomy and peeling of the membrane, using passive aspiration, a blunt retinal pick and aspiration forceps,” Dr. Massin told Ocular Surgery News. The preop and postop (3 months after surgery) examination included best corrected visual acuity using an Early Treatment Diabetic Retinopathy Study chart, as well as biomicroscopy of the fundus with a contact lens, fundus photography with blue and green monochromatic filters, fluorescein angiography and OCT.

“OCT was performed using commercially available equipment from Zeiss Humphrey Systems in [Dublin] California,” Dr. Massin said. The OCT examination entailed six radial 3-mm-long scans of each operated eye, centered on the patient’s fixation point. Retinal thickness was computed automatically using OCT software. Central macular thickness was assessed by averaging 14 measures 30 µm apart and located on two perpendicular scans (90° and 180°). “These were centered on the fixation point and constituted the diameters of a disk 320 µm wide,” she said.

In all instances, retinal thickness was measured preoperatively as the summed thickness of the epiretinal membrane and retina, “regardless whether the epiretinal membrane was distinguishable from the retinal surface,” Dr. Massin said. Preoperatively, all eyes had increased macular thickness (mean 419 µm; range 265.5 µm to 689 µm), along with disappearance of the foveal pit.

Thickness decrease

Postoperatively, macular thickness decreased significantly in 55 of the 62 eyes, with a mean decrease to 300 µm (range 185 to 511 µm). Macular thickness returned to normal in only 3 eyes, but the foveal pit reappeared in 20 eyes.

Study eyes achieved visual improvement comparable with most published studies. At 3 months postop, median visual acuity improved from 20/63 to 20/40. “The Early Treatment Diabetic Retinopathy Study score also gained an average of 11 letters, which is slightly more than two lines of vision,” Dr. Massin said. Overall, 82% of eyes reached 20/50 or better, compared with 32% before surgery.

“We had hoped there would be some correlation between visual acuity improvement and decrease of retinal thickness, but there was no correlation between postoperative central macular thickness and postoperative visual acuity,” Dr. Massin said. “There was a trend toward better vision when the foveal thickness was close to normal.”

Likewise, there was no correlation between preop macular thickness and visual outcome. “It may be that a 3-month postoperative period is too short to assess such correlations. Besides, macular thickness probably continues to decrease for several months after surgery,” she said.

Differential diagnosis

In addition to assessing retinal thickness, “OCT is very helpful in distinguishing macular pseudoholes from lamellar macular holes,” said Dr. Massin. In 10 of the 62 eyes, OCT showed changes in the foveal contour pit typical of a macular pseudohole.

“In these cases, the edges of the macula had thickened and the foveal pit contour was steeper, while the retinal reflectivity at the base of the pseudohole remained normal. These conditions allowed for an easy differential diagnosis with lesions that seemed ophthalmoscopically similar, such as a lamellar hole, full-thickness hole or macular cyst,” she said. The pseudohole disappeared in six cases postoperatively.

The study also detected 29 cases (46%) of peculiar heterogenous decreased backscattering of the outer layer of the macula (areas of hyporeflectivity), with cystic spaces in 15 spaces. “This may have been the result of fluid accumulation in the outer layers of the retina, as proposed by others,” Dr. Massin said. “However, we found fluorescein leakage in only 14 of these 29 cases, and only 3 of them exhibited cystoid edema on fluorescein angiography.”

For Your Information:

Pascale G. Massin, MD, can be reached at Department of Ophthalmology, Hôpital Lariboisière, Université Paris 7, Paris, France; (33) 1-49-95-64-88; fax: (33) 1-49-95-64-83; e-mail: p.massin@lrb.ap-hop-paris.fr. Ocular Surgery News could not confirm whether or not Dr. Massin has a direct financial interest in the products mentioned in this article or if she is a paid consultant for any companies mentioned.

For more information about the Optical Coherence Tomographer, contact Zeiss Humphrey Systems, 5160 Hacienda Dr., Dublin, CA 94568; (877) 486-7473; fax: (925) 557-4778.

Reference:

Massin PG, Allouch C, et al. Optical coherence tomography of idiopathic macular epiretinal membranes before and after surgery. Am J Ophthalmol. 2000;130:732-739.