COST line status may be useful prognostic factor after epiretinal membrane surgery

This retrospective case series in the April issue of the American Journal of Ophthalmology evaluated the prognostic value of the cone outer segment tips (COST) and other features using spectral-domain optical coherence tomography (SD-OCT) in patients undergoing epiretinal membrane (ERM) surgery. The authors found that the COST line was well delineated using SD-OCT and seemed to reflect the fine organization of photoreceptors. The status of the COST line strongly correlated with best-corrected visual acuity (BCVA) after ERM surgery, indicating its usefulness as a prognostic factor in conjunction with the inner segment/outer segment (IS/OS) junction.

Few studies have explored the significance of the COST line for visual function in ERM and other diseases. The authors studied a consecutive case series of 49 patients (50 eyes) who had undergone successful vitrectomy for idiopathic ERM and were followed for at least six months postoperatively.

They found no external limiting membrane disruption among any of the eyes. Six months after surgery, patients with a continuous photoreceptor IS/OS junction and COST line (group A) had significantly better BCVA than patients with a continuous IS/OS but disrupted COST line (group B; P < 0.005). Poorer BCVA was noted among patients with both a disrupted IS/OS and COST line (group C; P = 0.034).

Defect diameters of IS/OS and COST line were also significantly correlated with BCVA postoperatively. BCVA at six months ranked in order of best to worst was group A, B and C as assigned at baseline (P < 0.05) and one month postoperatively (P < 0.001). There was no significant correlation between central foveal thickness and BCVA.

While the early postoperative status of the COST line was critical for long-term visual prognosis, the preoperative COST status had a relatively weak correlation with BCVA at six months.