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Editors Selection IGR 16-3

Medical Treatment: Preservative free drops, cornea and tear-film

Comment by Malik Kahook on:

23773 An in vivo confocal microscopy analysis of effects of topical antiglaucoma therapy with preservative on corneal innervation and morphology, Martone G; Frezzotti P; Tosi GM et al., American Journal of Ophthalmology, 2009; 147: 725-735

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The use of topical ophthalmic medications remains the primary method for treating glaucoma and ocular hypertension. Much attention has recently been focused on the preservatives contained within these multi-dose bottles with mounting evidence suggesting that topical therapy might be linked to ocular surface disease.^1-3 Martone et al. (861) recently reported the results of a retrospective study designed to evaluate the long-term effects of preservative-free and preservative-containing anti-glaucoma drops on the cornea and tear film stability. Subjects used various types of preserved or unpreserved glaucoma drops and 20 control patients had no history of previous treatment. Testing consisted of esthesiometry, Schirmer I testing, and tear film break-up time (TFBUT). In vivo confocal laserscanning microscopy was also performed.

Studies on the use of preservative free and preservative containing anti-glaucoma drops should focus on merging clinical and diagnostic findings with patient-reported symptoms to tease out any significance to reported findings

Overall, the clinical tests did not show significant differences between the preservative-free and control groups. There was, however, a significant difference between the preservative-free and preservative groups. Confocal microscopy of the cornea showed differences in density of superficial epithelial cells, activated stromal keratocytes, and the number and tortuosity of sub-basal nerves. The authors concluded that glaucoma patients on chronic detergent preserved topical therapy 'show ocular surface alterations and that the development of nontoxic antiglaucoma treatment may reduce damage to the ocular surface and improve the compliance and the adherence in the medical therapy.' There are many shortcomings to this report. The authors stated that the study was retrospective, but then state that: 'informed consent was obtained from all patients prior to enrollment.' The use of central corneal imaging and the lack of uniformity in depth of scanned images between groups may have resulted in data unrepresentative of the true status of the tissue. Additionally, the lack of subjective evaluation of the study groups prevents correlating the clinical and diagnostic imaging findings with the true impact on patient comfort making any statements regarding adherence a major stretch. Future studies in this field should focus on merging clinical and diagnostic findings with patient reported symptoms to tease out any significance to reported findings. Furthermore, a crossover design appears imperative to validate findings. While studies in this realm are hampered by the lack of sensitive and reproducible metrics, studies like that performed by Martone et al. will help guide future researchers towards more solid evidence based medicine.

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