The Association of Chronic Topical Prostaglandin Analog Use With Meibomian Gland Dysfunction: Comment

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To the Editor:
The treatment armamentarium for managing glaucoma is limited. Majority of patients are still managed with topical antiglaucoma drugs, among which prostaglandin analog (PGA) are the first-line option in most cases. The article by Mocan et al1 was an interesting read as it highlighted a very important comorbidity of meibomian gland disease (MGD) associated with glaucoma patients. It is very rightly discussed in the above-mentioned article that these group of patients who already are susceptible to MGD because of their age, may worsen with PGA. However, we would like to highlight certain points which need further discussion.
MGD is a multifactorial disease,2 with age being a major risk factor. As per our own clinical experience, patients in this age group have mild to moderate MGD which may be symptomatic or asymptomatic. Therefore as also mentioned by the authors it would have been better to include pretreatment values to evaluate the impact of PGA on the development of, or worsening of the MGD.
In this study, the objective was to find the association between MGD and PGA drugs. However the results were given in the form of prevalence of MGD among various categories of drugs. It would have been better to find the association using odds ratio3 as one of the statistical methods to quantitate that association.
Third, as the study was specifically targeted to determine the association of PGA with MGD, it would have been appropriate to study 2 groups, PGA with benzalkonium chloride (BAK) and preservative free PGA with a control arm. Inclusion of other antiglaucoma medications (AGM) would create bias in the result interpretation as all AGM are known to cause a dry ocular surface. In this study all the patients were using PGA with BAK. As BAK is an independent risk factor for developing a dry ocular surface with lid changes due to its detergent action, so BAK itself could have potentiated the MGD.
Fourth, all patients with treatment for more than 1 year have been included. However, the duration of PGA use is not specified which can be a confounding factor in these patients. Long-term antiglaucoma treatment can be surface toxic.4 The chances of finding MGD in patients who are on AGM for a longer period of time are more than those on short period of time. Also, it is not mentioned whether the controls had any degree of MGD as age is a predisposing factor for development of MGD.
The authors have concluded that PGAs were more frequently associated with anatomic signs of MGD than non-PGA medications. Here, we would like to highlight that the power of the study has not been mentioned, and the number of patients in the PGA only group (25) is much higher than PGA with 1, 2, and 3 additional non-PGA medications (9, 10, and 2, respectively) which itself can cause bias in result interpretation.
With millions of patients on antiglaucoma treatment it is imperative to understand the association of the PGA and other AGM on the ocular surface including the lids. So, a well-designed prospective study with pretreatment and posttreatment evaluation is the need of the hour to choose the best possible treatment for our patients to help them have a good quality of life.
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