Discussion
Despite, on average, 65 cases of endophthalmitis being seen at Moorfields per year only 33 went on to have vitrectomy over a 5-year period. This small number reflects how restricted the indications for vitrectomy are. The majority of patients who present with endophthalmitis either have a good response to intravitreal therapy, insufficient view for vitrectomy or have reached NPL vision so are not considered for vitrectomy surgery
In our experience of vitrectomy surgery for all types of acute endophthalmitis, patients with exogenous endophthalmitis may gain increased visual benefit when surgery is performed within 7 days. Surgery can, however, be associated with a range of intraoperative and postoperative complications (24% risk of retinal detachment and 6% risk of losing the eye).
The EVS found 33% of patients who underwent vitrectomy with PL vision had VA of 6/12 or better and 56% had VA better than 6/36 at final follow-up.1 63% of our patients had PL vision prior to their vitrectomy surgery with the remainder having better vision. 11% of our patients had VA better than 6/12 at final follow-up and 26% had VA better than 6/36. Our results are also worse than the FRIENDS standards as already described. There are a number of different potential reasons for our worse visual outcomes.
1: Compared with the FRIENDS cohort and EVS, in our study, the inciting operation included not only cataract surgery but also trabeculectomy, corneal transplant, glaucoma drainage device surgery, intravitreal injection and vitreoretinal surgery. The rate of sight-affecting comorbidities was therefore higher in our cohort.
2.The timing of vitrectomy in EVS was within 6 hours, and the median time to vitrectomy surgery was 2 days in FRIENDS. In our hospital, as in most UK eye centres, we do not have a protocol to perform early vitrectomy surgery meaning that our average delay between presentation and vitrectomy was 8 days. Although small numbers, we found favourable improvements in vision for early vitrectomy for endophthalmitis following cataract surgery, vitrectomy surgery, and post-intravitreal injection therapy.
We hypothesise that the timing of vitrectomy surgery is important because the intravitreal environment associated with the natural history of endophthalmitis alters over time. In the acute stages, there is mainly vitreous infective debris and opacification that responds well to vitrectomy surgery. In the subacute phase, starting from 7 days over several weeks, the endophthalmitis condition is associated with abnormal vitreoretinal adhesions and vitreoretinal traction can develop and worsen during this time. We believe that these factors can lead to complications despite the newer modern instrumentation. Our study reports that earlier vitrectomy surgery can lead to better visual outcomes. This may reflect the progression of the inflammatory vitreoretinal interface, retinal ischemia, retinal thinning, retinal breaks and preretinal fibrosis that can develop if surgery is delayed.
Other case series of vitrectomy in endophthalmitis that have been published since the EVS have demonstrated mixed visual outcomes and surgical complication rates. In their editorial, Kuhn et al demonstrate some of the best results, yet to be repeated, for 47 cases: no cases of postoperative retinal detachment, enucleation or phthisis and 91% of patients achieving a final VA better than 6/12.2 They have not, however, published preoperative VA and there was no specific VA threshold prior to vitrectomy. It is difficult to interpret their results without clear preoperative VA data. In 2012, Alamanjourmia et al reported on 10 patients who underwent vitrectomy on average 2 days following diagnosis of endophthalmitis.4 All patients had POE following cataract or filtration surgery, with a preoperative VA of HM or worse. Eight (80%) patients achieved final VA of 6/18 or better, with complications of retinal detachment (20%), hypotony (10%) and choroidal detachments (10%). In contrast to these good VA results, Behera and coworkers demonstrated 16% of cases achieved VA better than 6/36, in a study of 31 cases undergoing early vitrectomy for fungal endophthalmitis.9 Complications included phthisis (25.8%), retinal detachment (3.22%) and evisceration (3.22%). Ho and co-workers in Australia have recently reported on 64 postoperative endophthalmitis patients with entry VA of Counting fingers (CF) or worse, who underwent vitrectomy surgery within 72 hours.10 The median time to vitrectomy was same-day surgery as per the EVS, and better outcomes were achieved for patients with HM or PL vision. However, there were complications of retinal detachment (9%) and evisceration (3%).
There are a number of limitations with this study. We report a selective case series that underwent vitrectomy surgery with no control group so it is not possible to compare our outcomes with a similar cohort of patients with medical management only. Due to the case series nature of our study, we cannot completely discount confounding factors in our results. Although we have shown better results with earlier vitrectomy, we cannot discount the possibility that an eye that has shown little sign of improvement at 4 days and might still improve by seven or 8 days. Thus, the eyes having earlier vitrectomy might have done better than those having late vitrectomy regardless of whether or not they had a vitrectomy.
The wide diversity of aetiologies of endophthalmitis, which may be a reflection of our institution, should also be acknowledged as another potential source of confounding.
Although the diversity of aetiologies is a potential source of confounding, we think this study with its wide range of aetiologies is important. Intravitreal injections are the biggest treatment change in the past 10 years for age-related macular degeneration (AMD) and diabetic macular oedema (DMO). The incidence rates of POE vary between 0.038 and 0.053.11 12 In the EVS, patients were excluded based on pre-existing visual impairment secondary to other ocular conditions so benefits of contemporary early vitrectomy surgery in patients with POE with AMD and DMO cases remains unclear. In glaucoma, bleb-associated POE has a poor visual outcome; vitrectomy surgery in these cases has been shown to produce more favourable outcomes for patients.13
Due to the rarity of endophthalmitis, the numbers involved were not large enough for the regression analysis of delay in surgery to be significant (p=0.112) but there was a negative VA gain trend with increase delay in surgery (see figure 2). As the study was retrospective, it was designed largely to detect trends that could direct future research rather than powered for analysis.
EVS guidance of vitrectomy within 6 hours is not compatible with current intravitreal antibiotic treatment protocols for endophthalmitis in the UK. Good results are frequently obtained from the standard of care for endophthalmitis, intravitreal injections, so any future randomised clinical trial examining early vitrectomy for acute endophthalmitis should have medical therapy as the comparator control group.6