Membrane Contraction Contributes to Increase in Choroidal Thickness in Patients With ERM

In patients with idiopathic epiretinal membrane (ERM), membrane contraction contributed to the increase of choroidal thickness, according to study results published in PLoS ONE.

ERM can induce differing degrees of blurred vision and metamorphopsia (a visual defect that distorts linear objects); in early stages, it is characterized by an abnormal retinal light reflex on fundoscopy with mild retinal thickening and no distortion of the retinal surface, researchers explained.

“However, as the membrane becomes thicker, it may cause retinal folds, excursion, or tortuosity of retinal vessels, resulting in increased retinal thickness, macular edema, and disturbances in macular micro-circulation.”

Several macular diseases, including age-related macular degeneration, have been shown to be associated with changes in choroidal thickness, but no data have been published evaluating the influence of different morphological optical coherent tomography (OCT) findings on choroidal thickness in idiopathic ERM.

To compare the macular choroidal thickness of idiopathic ERM and fellow (healthy) eyes before and after vitrectomy, investigators used spectral-domain OCT (SD-OCT) to assess morphological features.

In the retrospective study, researchers analyzed medical records of patients diagnosed with idiopathic ERM who presented to a hospital in Taiwan between January 2014 and June 2017.

A total of 84 patients presented with unilateral ERM, and all were classified into 3 groups. Patients in group 1 had ERM without membrane contraction (n = 20), those in group 2 had ERM with membrane contraction and associated retinal folding (n = 27), and group 3 (n = 37) consisted of patients who had ERM with membrane contraction and macular edema.

Mean (SD) patient age was 64.9 (9) years, and the majority (56%) were women. There were no statistically significant differences in age, percentage of women, or hypertension among the 3 groups, although individuals in group 1 tended to have better visual acuity than those in groups 2 and 3 (P = .019).

Analyses revealed:

• The ERM eyes and fellow eyes within each group had no statistically significant difference in mean axial length
• Mean (SD) choroidal thickness was significantly greater in ERM eyes than in fellow eyes (234.4 [22.5] vs 220.6 [20.8] mcm; P < .01)
• Group 1 showed no significant difference in choroidal thickness between ERM and fellow eyes
• Eyes in group 2 and group 3 showed statistically significant differences in mean (SD) choroidal thickness between ERM and fellow eyes (229.6 [23.8] vs 220.8 [19.6] mcm and 242.6 [27.8] vs 221.0 [21.8] mcm, respectively; P<.05)
• Of the patients who underwent vitrectomy and surgical removal of ERM (n = 24), in group 2 (n = 8) and group 3 (n = 16), choroidal thickness in ERM eyes decreased significantly at 1 month and 6 months after surgery, compared with that before surgery (P < .05 for all comparisons)

Taken together, researchers claimed the results indicate that membrane contraction contributes to the increase in choroidal thickness in patients with idiopathic ERM.

Small sample sizes and short-term follow-ups mark limitations of the study, and because patients in group 1 had generally good visual acuity, no patients in the group underwent surgery. Researchers therefore could not determine the change in choroidal thickness among patients without macular traction.

To reduce potential bias and confirm results, further studies with larger cohorts of patients are warranted.

Overall, the findings “may help to elucidate the pathophysiologic features of idiopathic ERM as well as the response to treatment in these patients,” authors concluded.

Reference

Fang I, Chen L. Association of macular choroidal thickness with optical coherent tomography morphology in patients with idiopathic epiretinal membrane. PLoS One. Published online September 29, 2020. doi:10.1371/journal.pone.0239992