Purpose To investigate the impact of cigarrete smoking in a group of otherwise healthy young individuals on: 1) Retinal blood flow using Doppler based SD-OCT, 2) Retinal vascular reactivity using a gas sequencer to provoke hypercapnia via constant changes in PETCO2 (end-tidal partial pressure of CO2) and in PETO2 (end-tidal partial pressure of O2). Methods An automated gas flow controller was used to achieve normoxic hypercapnia in ten non-smokers (mean age 28.9 yrs, SD 4.58) and nine smokers (mean age 27.55 yrs, SD 4.77). Retinal blood flow measurements were obtained using Doppler OCT and cannon laser blood flowmeter (CLBF) during baseline, normoxic hypercapnia (15% increase in PETCO2 relative to homeostatic baseline) and post-hypercapnia in both the groups. Exhaled carbon monoxide level was measured in all subjects. Results In non-smokers, retinal arteriolar diameter, blood velocity and flow increased by +4.1% (SD 2.8, p<0.0001), +16.7% (SD 14.6, p=0.0004) and +29.6% (SD 12.5, p<0.0001) respectively, during normoxic hypercapnia; Similarly, the venous area, venous velocity and total retinal blood flow increased by 7% (SD 8.6, p=0.0418), 18.1% (SD 20.8, p=0.0068) and 26% (SD 22.9, p<0.0001) respectively. In smokers, normoxic hypercapnia resulted in a significant increase in velocity by 12.0% (SD 6.2, p=0.0019) and flow by 14.6% (SD 9.5, p=0.0029); though arteriolar diameter increased by 1.7% (SD 1.7, p=0.2616), the result was not statistically significant. Total retinal blood flow increased significantly by 19.3% (SD 18.4, p=0.002) in response to normoxic hypercapnia. However, there was no significant difference in venous area (p=0.3322) and venous velocity measurements (p=0.1185) during hypercapnia compared to baseline and recovery. Comparing smokers and non-smokers, only the percentage change in arteriolar diameter (p=0.0379) and flow (p=0.0101) was significantly different among the groups. Group mean PETCO2 was increased by 15.9% in the non-smoking group and by 15.7% in the smoking group, with a concomitant increase in PETO2 by approximately 1.5 to 2% in both groups. There was no significant difference in baseline PETCO2 level between smokers and non-smokers. Conclusions Retinal vascular reactivity in response to normoxic hypercapnia is significantly reduced in young healthy individuals who smoke compared to non-smokers. Further studies are needed to elucidate the exact reason behind the impaired retinal autoregulation to provocative stimuli in smokers.

Purpose To investigate the impact of cigarrete smoking in a group of otherwise healthy young individuals on: 1) Retinal blood flow using Doppler based SD-OCT, 2) Retinal vascular reactivity using a gas sequencer to provoke hypercapnia via constant changes in PETCO2 (end-tidal partial pressure of CO2) and in PETO2 (end-tidal partial pressure of O2). Methods An automated gas flow controller was used to achieve normoxic hypercapnia in ten non-smokers (mean age 28.9 yrs, SD 4.58) and nine smokers (mean age 27.55 yrs, SD 4.77). Retinal blood flow measurements were obtained using Doppler OCT and cannon laser blood flowmeter (CLBF) during baseline, normoxic hypercapnia (15% increase in PETCO2 relative to homeostatic baseline) and post-hypercapnia in both the groups. Exhaled carbon monoxide level was measured in all subjects. Results In non-smokers, retinal arteriolar diameter, blood velocity and flow increased by +4.1% (SD 2.8, p<0.0001), +16.7% (SD 14.6, p=0.0004) and +29.6% (SD 12.5, p<0.0001) respectively, during normoxic hypercapnia; Similarly, the venous area, venous velocity and total retinal blood flow increased by 7% (SD 8.6, p=0.0418), 18.1% (SD 20.8, p=0.0068) and 26% (SD 22.9, p<0.0001) respectively. In smokers, normoxic hypercapnia resulted in a significant increase in velocity by 12.0% (SD 6.2, p=0.0019) and flow by 14.6% (SD 9.5, p=0.0029); though arteriolar diameter increased by 1.7% (SD 1.7, p=0.2616), the result was not statistically significant. Total retinal blood flow increased significantly by 19.3% (SD 18.4, p=0.002) in response to normoxic hypercapnia. However, there was no significant difference in venous area (p=0.3322) and venous velocity measurements (p=0.1185) during hypercapnia compared to baseline and recovery. Comparing smokers and non-smokers, only the percentage change in arteriolar diameter (p=0.0379) and flow (p=0.0101) was significantly different among the groups. Group mean PETCO2 was increased by 15.9% in the non-smoking group and by 15.7% in the smoking group, with a concomitant increase in PETO2 by approximately 1.5 to 2% in both groups. There was no significant difference in baseline PETCO2 level between smokers and non-smokers. Conclusions Retinal vascular reactivity in response to normoxic hypercapnia is significantly reduced in young healthy individuals who smoke compared to non-smokers. Further studies are needed to elucidate the exact reason behind the impaired retinal autoregulation to provocative stimuli in smokers.

Optical coherence tomography systems are used to image the retina in 3D to allow ophthalmologists diagnose ocular disease. These systems yield large data sets that are often labor-intensive to analyze and require significant expertise in order to draw conclusions, especially when used over time to monitor disease progression. Spectral Domain Optical Coherence Tomography (SD-OCT) instantly acquires depth profiles at a single location with a broadband source. These systems require mechanical scanning to generate two- or three-dimensional images. Instead of mechanically scanning, a beamlet array was used to permit multiple depth measurements on the retina with a single snapshot using a 3x 3 beamlet array. This multi-channel system was designed, assembled, and tested using a 1 x 2 beamlet lens array instead of a 3 x 3 beamlet array as a proof of concept prototype. The source was a superluminescent diode centered at 840nm with a 45nm bandwidth. Theoretical axial resolution was 6.92um and depth of focus was 3.45mm. Glass samples of varying thickness ranging from 0.18mm to 1.14mm were measured with the system to validate that correct depth profiles can be acquired for each channel. The results demonstrated the prototype system performed as expected, and is ready to be modified for in vivo applicability.