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Editor,—We read with interest the article by Culliance and Cleary1 on the method of prevention of visual field defects after macular hole surgery. In their series, one group of 82 eyes received conventional pars plana vitrectomy surgery with mechanical induction of posterior vitreous detachment (PVD) around the optic disc followed by complete posterior cortical vitreous removal. Twenty two per cent of these eyes had certain postoperative visual field defects. There again, another group of 20 eyes received pars plana vitrectomy with peeling of the posterior hyaloid confined to the macular area with sparing of the peripapillary region. None of them had any postoperative visual field loss. The authors proposed that vitreopapillary traction around the optic nerve head during the mechanical separation of the posterior hyaloid is responsible for the formation of the observed postoperative inferotemporal visual field defects. The microcirculation at the optic nerve head may be damaged during the induction of PVD as the posterior cortical vitreous is most adherent at the superonasal aspect of the optic disc.2However, we are concerned about the standardisation of the method of removing the remaining peripheral cortical vitreous in these two groups of eyes, as peripheral vitreous may act as a protective cushion from dehydration during fluid/air exchange. Yan et al 3 had shown that no significant correlation was found between iatrogenic detachment of vitreous cortex and postoperative visual field defect, but all patients who had postoperative visual field defect had undergone fluid/air exchange in their series. Similarly, Ohji et al 4 had demonstrated that using humidified air for fluid-air exchange in macular hole surgery could prevent postoperative visual field defect. Others had demonstrated that the visual field defect was dependent upon the site of the air infusion port.5 6 All these reports suggest that air dehydration of the peripheral retina may be a very important factor in causing postoperative visual field defect after macular hole surgery.
In conclusion, we congratulate Culliance and Cleary1 on their study describing the prevention of visual field defects after macular hole surgery by limited posterior hyaloid peeling. However, the exact mechanism behind this success needs further evaluation.
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