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Poon et al1 in their excellent article have reiterated the efficacy of autologous serum in the treatment of persistent epithelial defects (PEDs) of the cornea. We would like to invite the attention of the authors to certain aspects of the study.
The authors have considered a period of 1 week for labelling an epithelial defect to be persistent. However, most studies on a similar subject have taken the criterion to be 2 weeks.2
It is generally recommended that a “washout” period of at least 2 weeks be given with preservative free artificial tears3 and only those epithelial defects that remain either static or demonstrate an increase in size in this period be included in the study. The authors have not mentioned such a washout period being included in the protocol. When using autologous serum drops most investigators have not used any other therapeutic modality at the same time to enhance epithelialisation, apart from preservative free lubricants. The use of therapeutic contact lenses in five cases by the authors makes it difficult to evaluate the actual contribution of serum drops in the healing of the epithelial defect in these cases. Further, the use of serum drops in the immediate postoperative period in two patients with poor ocular surface undergoing keratoplasty without waiting for the corneal epithelial defect to heal by itself cannot be extrapolated to making a comment on the beneficial effect of autologous serum. Also the rationale behind the use of 100% serum when previous studies have proved the efficacy of a 20% solution2 is not understandable. This concentrated serum can cause stickiness, which would be inconvenient to the patients and may reduce the compliance. The use of the slit lamp micrometre by the authors for measuring the epithelial defects may not be accurate because of its inherent interobserver and intraobserver variations. A better method would be measuring the area of the defect instead of the greatest dimensions by the use of digital photographs and area measuring software such as Image Pro Plus available from Media Cybernetics.
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