We conducted a prospective cohort study which adhered to the Declaration of Helsinki. Institutional Review Board approval was obtained and all subjects gave informed consent prior to enrollment into the study.
Study participants consisted of consecutive cohort of patients who underwent phacoemulsification with intraoperative complication in the University of Malaya Medical Center between July 2009 and June 2010. Intraoperative complication was defined based on similar studies and included the presence of any of the following conditions, whether in isolation or in combination: posterior capsule rent, zonulodialysis, presence of vitreous loss, dropped nucleus, complications needing enlargement of the corneal wound or a second operation and position of the intraocular lens other than in-the-bag
All patients 21 years of age or older with sufficient media clarity to permit preoperative OCT evaluation were eligible for inclusion in the study. Our exclusion criteria included patients on prostaglandin analogues, topical or systemic steroid or non streroidal anti-inflammatory drugs, history of uveitis, prior intraocular injections or surgery, past or pre-existing retinal and choroidal diseases that could affect retinal thickness. These included but are not limited to CMO, diabetic retinopathy or maculopathy, retinal vein occlusion, age-related macular degeneration, radiation retinopathy, posterior uveitis and previous laser treatment. Subjects with abnormal macula based on clinical examination and preoperative macular OCT scans were excluded from this study.
Initial screening was conducted during subjects’ preoperative visits two weeks prior to their scheduled phacoemulsification. We obtained patient’s detailed history and performed ophthalmologic examination that included BCVA, slit-lamp biomicroscopy, intraocular pressure measurement, dilated fundus examination and OCT scans. Throughout this study, BCVA was performed with refraction. It was measured using a back-illuminated Snellen chart at 6 meters and converted to logarithm of minimal angle of resolution (logMAR) scale for analysis. SD-OCT (Cirrus; Carl Zeiss Meditech, Inc, Jena, Germany) scanning was done using the macular cube scan (512×128 scan pattern) centered on the fovea. Scans with signal strength 6 or greater were deemed acceptable. All OCT scans for this study were performed by two of the authors (KWK and HHL).
From the preoperative screening, 805 subjects who met the inclusion and exclusion criteria were identified. All consented for the study. From these, 48 eyes of 48 patients experienced intraoperative complication during phacoemulsifiction. They were subsequently reviewed at 1 week, 6 weeks and 16 weeks postoperatively
[6–8]. At each visit, BCVA, slit-lamp examination and OCT scan were performed. One patient did not complete the scheduled follow up. A patient is defined as belonging to the CMO group if he or she developed CMO at week 16.
After phacoemulsification, all patients received standardized topical steroid and antibiotic drops. This involved two-hourly topical administration of prednisolone acetate 1% (Pred Forte, Allergan, Irvine, CA) for the first week, four times daily for one month and then subsequently tapered. Topical antibiotics were given four times daily during the same period.
Upon the detection of CMO, a step-wise treatment approach was employed. In the first instance, correctable causes like vitreous traction at the wound were addressed. Subsequently, topical steroid application was intensified and topical non-steroidal anti-inflammatory drug was added. No patients with CMO in our series needed more invasive approaches such as the use of sub-Tenon or intravitreal triamcinolone and/or intravitreal anti-vascular endothelial growth factor.
Data collection included demographic characteristics, ocular and medical history as well as intraoperative details such as surgeon’s experience (resident or consultant ophthalmologist), operation time, type of complication and intraocular lens position.
The main outcome measure was the rate of postoperative CMO. This was defined as the presence of hyporeflective intraretinal cystoid changes noted on SD-OCT which was not present preoperatively
. It was graded by a single consultant ophthalmologist (VS) who was masked from the patient’s intraoperative complication, visual acuities and treatment approach. Secondary outcomes included mean macular thickness and BCVA, compared between patients who developed postoperative CMO against those who did not.
Since the patterns of visual improvement dependency on change in macular thickness for the CMO and non-CMO group across four time points may be complex, we explored the data graphically using the scatter plot and the heat plot. The latter is a powerful graphical method that is commonly used for exploring patterns in multidimensional data, such as those from genomic studies
. For statistical analysis, paired t-test was used to test for significant difference in mean macular thickness and BCVA between baseline and at 16 weeks for both the CMO and non-CMO groups. To compare the discrepancy of mean macular thickness between these two groups at baseline and at 16 weeks, we used the two-sample t-test with Bonferonni adjustment (5% significance level). All graphical plots and statistical analyses were done using R Version 2.13.2