To the Editor.
—It would be unreliable to attempt to draw firm conclusions from the study by Coleman et al1 in the September 1990 issue of the Archives. The most obvious and fatal flaw is the absence of a control group, which makes it impossible to be certain that the observations did not arise due to the passage of time. Added to this is the small sample size. Only 28 of the 40 volunteers, who were recruited, completed 60 days of the study.The changes in high-density lipoprotein (HDL) cholesterol levels (from 1.45 mmol/L to 1.32 mmol/L) were within the normal ranges for volunteers and would not have been regarded as clinically important. It has been found that in volunteers in a placebo-controlled study, lipid lowering agents were not able to decrease levels of HDL cholesterol by 9%. It remains highly likely that the observed changes in the study
Vogel R. Topical Timolol and Serum Lipoproteins. Arch Ophthalmol. 1991;109(10):1341. doi:10.1001/archopht.1991.01080100021004