Effects of coronary artery bypass grafting surgery on retinal vascular caliber, ocular pulse amplitude and retinal thickness measurements

Aim:

The retina and ocular vasculature are vulnerable to alterations in systemic hemodynamics, such as in open heart surgeries. Our aim was to investigate 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.

Methods:

Twenty-six patients who had a history of CABG surgery and 26 age-sex-matched healthy participants were recruited for this prospective, cross-sectional and comparative study. The RVC, peripapillary RNFL and macular thickness measurements were taken with spectral-domain optical coherence tomography. The OPA, a surrogate of pulsatile ocular blood flow, was measured with the Pascal dynamic contour tonometer.

Results:

There were no statistically significant differences between the CABG surgery patients and the controls with regard to RVC, OPA, peripapillary RNFL thickness and macular thickness measurements (p>0.05).

Conclusions:

CABG surgery does not affect retinal structures and pulsatile ocular blood flow in the long-term follow-up.

Intraocular pressure during cardiopulmonary bypass

Intraocular pressure was measured in 24 patients undergoing elective cardiopulmonary bypass surgery. There was a rapid rise when the bypass circulation began, and this was maintained for about 30 minutes. A simultaneous drop in arterial perfusion pressure and packed cell volume occurred. We suggest that marked haemodilution is responsible for this effect, through increased ocular blood flow and low colloidal osmotic pressure. The possible aetiological significance in relation to ischaemic optic neuropathy complicating cardiopulmonary bypass is discussed.

Intra-ocular pressure levels during extracorporeal circulation in man

Intra-ocular pressure, arterial blood pressure and central venous pressure were recorded before, during and after open-heart surgery in 12 patients. In contrast to previous findings by others, no increase in intra-ocular pressure was observed during the perfusion period. The discrepancy may be explained by differences in composition of the priming solution and the degree of haemodilution during perfusion. Attention should be paid to any sudden increase in central venous pressure after the end of extracorporeal circulation, as this may produce a corresponding increase in intracranial pressure.

The effect of haemodilution on arterial blood pressure, central venous pressure, intracranial and intra-ocular pressures in pigs

During the open-heart surgery, haemodilution is performed before extracorporeal circulation is started by the sampling of autologous blood and substituting an electrolyte solution. Following extracorporeal circulation, first the machine-blood and then the autologous blood is reinfused. The haemodilution and reinfusion procedures lead to alterations in blood osmolality and tissue fluid distribution, initiating changes in arterial blood pressure, central venous pressure, intracranial and intraocular pressures. These changes were studied in pigs. It is believed that these potentially hazardous pressure alterations can be minimized through proper handling of the procedure. This study presents some of the mechanisms involved.

Intra-ocular pressure before, during and after extracorporeal circulation in pigs

Variations in intra-ocular pressure (IOP) were demonstrated before, during and after extracorporeal circulation in pigs. Most probably both the observed increase and reduction in IOP may be explained by corresponding changes in blood osmolality, blood pressure and body temperature. In contrast to clinical findings, no increase in IOP was observed during the period of extracorporeal circulation.