Appropriate evaluation of ocular parameters in coronary artery bypass grafting surgery patients

We read with great interest the recently published article “Effects of coronary artery bypass grafting surgery on retinal vascular caliber, ocular pulse amplitude and retinal thickness measurements” by Pekel et al.1 In this study, the researchers analyzed retinal vascular caliber (RVC), ocular pulse amplitude (OPA), peripapillary retinal nerve fiber layer (RNFL) and macular thickness in coronary artery bypass grafting (CABG) surgery patients. In conclusion, the authors stated that CABG surgery did not affect retinal thickness, retinal vessels or pulsatile ocular blood flow in the long-term followup. However, we think that there are some points that should be emphasized about this study. First, as is known, the use of secondary prevention medications (antiplatelet agents, statins, beta-blockers and angiotensin-converting inhibitors) are important to reduce the risk for recurrent cardiovascular events after CABG.2,3 In a study by Stenman et al., it was observed that 93% of patients had at least two dispensed prescriptions for an antiplatelet agent, 68% for an angiotensinconverting enzyme inhibitor/angiotensin II receptor blocker, 91% for a beta-blocker, 92% for a statin and 57% of all patients had prescriptions for all four medication classes during the first year after CABG.4 Also, in a study by De Castro et al., it was reported that the use of statins for at least 23 months showed optic nerve head changes suggestive of a protective effect against glaucoma progression and RNFL thickness.5 Therefore, it would be better to consider the medication status while performing RVC, OPA, RNFL and macular thickness measurements. Second, we suggest to the authors that they present the details of the laboratory parameters used to exclude systemic diseases, such as diabetes mellitus and systemic hypertension, which may affect ocular structures. As a matter of fact, prediabetes (impaired fasting glucose and impaired glucose tolerance), as well as diabetes mellitus, increases the risk of glaucoma and induces a significant loss of macular function.6,7 This issue should be considered to avoid patient selection bias. Therefore, it would be better to perform at least 2-h oral glucose tolerance tests (OGTT) to evaluate the presence of prediabetes in the original study. In conclusion, the use of secondary prevention medications which may possibly affect RVC, OPA, peripapillary RNFL and/or the macular thicknesses in patients with CABG should be considered in the original study.