Dovepress 20 gauge group. There are a number of possible explanations for this. TSV utilizes a cannulated entry system which may reduce vitreous base traction during instrument insertion. Indeed, Territto et al demonstrated a lower occurrence of retinal breaks located near the sclerotomy sites using a cannulated entry system in a randomized controlled trial of 77 eyes undergoing vitrectomy for a variety of indications.19 This is particularly important in diabetic vitrectomy where instrument exchange is more frequent and scissors are often used. Oyakawa et al previously showed that most peripheral breaks in diabetic vitrectomy are sclerotomy related and commoner on the side of the surgeon’s dominant hand.20 Ramkissoon et al confirmed this, but only in cases operated on for tractional retinal detachment where more complex dis- section was needed. Therefore, cannulated entry systems are of particular relevance in diabetic vitrectomy compared with vitrectomy for macular surgery, where sclerotomy located tears are less common.3 Angled scissors commonly used for delamination with 20 gauge surgery cannot be used with cannulated entry systems, and it is likely that there is reduced traction during insertion of the straight or curved instruments used for TSV surgery. Indeed, a change of delamination technique to achieve membrane removal is required with TSV for complex dissections. The introduction of TSV coincided with advancements in vitrectomy cutter design and, in particular, a reduced cutter tip to port distance. The 20 gauge Innovit cutter used has a tip to port distance of 0.38 mm whilst the corresponding distance for the 23 gauge Accurus and Con- stellations cutters is 0.23 mm. This, along with the narrower profile of 23 gauge and 25 gauge, allows greater use of cutter delamination and dissection. This technique, along with a technique of bimanual cutter dissection with end gripping forceps to retract tissue whilst cutting, means that scissors are less frequently required to delaminate membranes. Indeed, in our series, scissors were used in 35% of the 20 gauge cases compared with 6% of the TSV cases, despite a similar case mix. The 23 gauge Accurus and Constellation cutters also have a higher maximum cut rate of 2500/5000 cuts per minute compared with the 20 gauge Innovit cutter which can go up to 1800 cuts per minute. Higher cut rates result in a lower volume of aspirated tissue per cut at a fixed flow and hence may reduce tissue traction which may, in turn, affect break rate. The greater use of cutter delamination may thus partly also explain the lower rate of posterior and sclerotomy-related breaks we observed with the 23 gauge TSV. Importantly, this also means it is possible that a cannulated 20 gauge system with a new generation cutter would achieve similar results. Clinical Ophthalmology 2011:5 retinal breaks in transconjunctival vitrectomy The rate of peripheral retinal break formation located away from the sclerotomies, and related mainly to the induction and propagation of a posterior vitreous detachment, was not appreciably different between the two groups. It may be that this study was not large enough to show such a difference but it is perhaps not surprising that there was marked difference because the technique of propagation of a PVD using TSV is the same as that used during 20 gauge surgery. There are a number of possible confounders in this study which require consideration and these will now be discussed. Firstly, it has been shown that retinal break formation in diabetic vitrectomy is related to the complexity of the case.3,4 Sullivan found peripheral retinal breaks in 22% of tractional retinal detachment cases compared with 13% of more straightforward vitreous hemorrhage cases. Yorston et al found that the risk of posterior retinal break formation was related to increased vitreoretinal adhesion and tractional retinal detachment at the macula, both of which were related to the complexity of dissection required.2 Sclerotomy site breaks were also more common in younger patients. It is thus important to demonstrate that the two groups were matched as closely as possible in our series; we found no significant difference in any of the preoperative values between the two groups, and the groups were well matched in terms of surgical complexity (Table 1). Oshima et al found a lower rate of retinal break formation with 23 gauge surgery for a series of diabetic vitrectomies as compared with 20 gauge surgery, but the 23 gauge group patients had preoperative bevacizumab administered, reducing the complexity of dissection required.10 None of our patients in the two groups had bevacizumab either preoperatively or intraoperatively, thus avoiding this confounding factor. Secondly, it is important to consider the possibility that retinal breaks could have been missed in the TSV group. We think this is unlikely. The surgeries were performed by a single surgeon, and the same retinal inspection regime was used in both groups, with the same wide angle viewing system. As with two other series we also reported possible retinal breaks, which showed the same trend as definite breaks between the two groups of patients.5,21 We had two cases of postoperative retinal detachment which were related to recurrent posterior tears which reopened in known breaks that had been treated. Our rate of postoperative retinal detachment was low in both groups at 1% compared with previous reported rates of 3%–18%.1 We had at least six months postoperative follow-up in all patients, and it is unlikely that we missed any postoperative retinal detachment. Careful internal search and treatment of all breaks and lesions which submit your manuscript | www.dovepress.com Dovepress 113