Dear Editor,

I applaud the authors for attempting to address the issue of microbial contamination of preservative free (PF) eye drops in multiple application containers but wish to highlight a few points.

Although informed consent have been obtained from patients prior to analysing their eye drops, it is surprising that ethical committee approval was not sought before starting the study.

The authors have stated that the ‘safety period for multidose containers is arbitrary … not evidence based’. However, Oldham et al1 tested 21 different unpreserved multidose eyedrop formulations to establish their inherent efficacy in antimicrobial preservation and concluded that once opened by individual patients in a domiciliary situation, a 7 day in use storage life is confirmed for unpreserved eye drops containing alkaloids or antibiotics, if they are stored in the refrigerator after opening.

There has been no mention of any exclusion criterion in the selection of patients. Previous studies evaluating the issue of contamination of eye drops have either excluded patients with infected ocular surface disorders2,3 or have taken a conjunctival / corneal swab4 to evaluate whether the same microorganism was recovered from the conjunctiva and from the contaminated medication. Also, as rightly pointed out by Sher A Aslam et al5, it has been assumed in the study that the multidose containers were sterile at the time of dispensation. These two factors may invalidate the actual incidence of contamination of the eye drops in the study. Also, it does not throw any light as to whether all the contaminants isolated were truly exogenous or not.

Apparently elderly patients and those with reduced visual acuity or coordination are the ones who are most likely to inadvertently touch the tip of the dropper to the external suface. Also, the incidence of contamination of an eye drop which is being used hourly is more likely than one which is being used two or three times a day. Hence it would be interesting to know whether there is a correlation between age, visual acuity and frequency of administration of drops and incidence of contamination. Ultimately the onus remains on the medical practitioner to ensure that the unpreserved multidose eyedrops are only used in appropriate circumstances to ensure safe and effective therapy. Therefore, any significant finding in this regard may raise a question as to whether it is good practice to prescribe unpreserved multidose eyedrops to these vulnerable group of patients.

REFERENCES ----------

1. Oldham GB, Andrews V. Control of microbial contamination in unpreserved eyedrops. Br J Ophthalmol. 1996 Jul;80(7):588-91

2. Livingstone DJ, Hanlon GW, Dyke S. Evaluation of an extended period of use for preserved eye drops in hospital practice. Br J Ophthalmol. 1998 May;82(5):467.

3. Schein OD, Hibberd PL, Starck T, Baker AS, Kenyon KR. Microbial contamination of in-use ocular medications. Arch Ophthalmol. 1992 Jan;110(1):82-5.

4. Geyer O, Bottone EJ, Podos SM, Schumer RA, Asbell PA. Microbial contamination of medications used to treat glaucoma. Br J Ophthalmol. 1996 Mar;80(3):270.

5. Aslam SA, Malik N. Contamination of preservative free eye drops. eLetter: BJO (19 April 2006)