Refractive Consequences of Epiretinal Membrane Surgery

Aim: To evaluate the impact of the sequence of surgery on the Refractive Error and the Corneal Endothelial Count in phakic individuals undergoing surgery for Epiretinal membrane.

Study design: Prospective interventional randomized clinical trial. Primary outcome: Refractive error (i.e. Intraocular lens power prediction error), Corneal Endothelial Count, and postoperative macular oedema.

Secondary outcome: Changes in axial length, anterior chamber depth and keratometry; the accuracy of formulas used to calculate the power of the intraocular lens.

Study population:

Identification of participants: Individuals referred to the Macular Surgery Clinic, Surgical Retina Team, Department of Ophthalmology, Glostrup University Hospital, Copenhagen, Denmark. The individuals should be signed up for surgery because of Epiretinal membrane at the clinic.

Method:

Individuals are randomized to the possible sequences of surgery (i.e. start with cataract surgery, start with vitrectomy, or combined surgery). Based on an estimated clinical relevant refractive prediction error of 0,50 diopter and a standard deviation of 0,50 diopter, a number of 20 individuals in each of the three groups are needed to obtain a power of 80 % and a type 1 error of 5 %. Total number of individuals is thus 60.

Clinical examinations are performed preoperatively and 2 weeks after each surgery (cataract surgery, vitrectomy or combined surgery), and 3 and 12 months postoperatively. The examinations include best corrected distance visual acuity, autorefraction/keratometry (Retinomax®, Nikon, Tokyo, Japan), subjective refraction, slit-lamp examination, fundoscopy and tonometry. Biometry by IOLMaster (Carl Zeiss, Meditec AG, Germany), intraocular power calculation with the SRK/T formula. Pentacam Scheimpflug Cornea tomography (Topcon, Tokyo, Japan). Corneal Endothelial Count obtained by three images of the central region of the corneal endothelium (Topcon SP-3000P, Tokyo, Japan). Heidelberg Optical Coherence Tomography, (Heidelberg Engineering, Heidelberg, Germany).

Sequence of surgery depends on randomization. In all cases a standard phacoemulsification (scleral tunnel or clear corneal incision) with in-the-bag intraocular lens implantation. In combined surgery, the cataract surgery is performed before vitrectomy during the same session. Vitreoretinal procedures include a standard three-port 23 gauge pars plana vitrectomy, membrane peeling, and the use of dyes. Cataract surgery is performed by one of two experienced surgeons, and vitrectomy is carried out by one experienced surgeon.

Analysis: A computer database will be created as a fill-in form to record all patient data, and a masked statistical analysis of all outcome measures will be performed. Statistical analysis will be performed to determine differences in baseline data among the three groups (age, sex, visual acuity, keratometry, axial length, anterior chamber depth, Corneal Endothelial Count). To identify independent predictors for all outcome measures at different follow-up times, multivariate regression analysis is performed. All calculations will be performed using SAS software.

Inclusion criteria

• A diagnosis of Epiretinal membrane,
• visual complaints consistent with Epiretinal membrane,
• age more than 50 years,
• refraction less than ± 5 diopters and astigmatism less than 3 diopters,
• indication for vitrectomy is only Epiretinal membrane.

Exclusion criteria

• Previous intraocular surgery or laser-refractive procedure.
• Use of intraocular gas tamponade during the vitrectomy.
• Intraoperative manipulation of the intraocular lens.
• Serious complications (endophthalmitis, vitreous haemorrhage or retinal detachment).
• History of previous head or ocular trauma.
• Sulcus fixation of intraocular lens