Effect of Screen Distance on Colonic Polyp Detection and Colonic Polyp Size Estimation: A Pilot Study

Background Colorectal cancer is the 3rd most common cancer in the world, with about 1.2 million new cases reported annually. It is one of the three most common causes of cancer related mortality in Europe and North America. Thus, prevention and detection are critical aspects in managing colorectal cancer. Colonoscopy remains the gold standard for screening of colorectal cancer, as it is valuable not only for detection but also prevention with polyp identification. Adenoma detection rate remains a pivotal part of a good endoscopic exam. While various factors have been known to influence it, data regarding ideal screen distance for adenoma detection remains unclear. The aim of this study was to assess the rate of polyp detection and estimate the size of diminutive (<1 cm) polyps with varying screen distance from the proceduralist. Materials and Methods This was a quality improvement project carried at OSF Saint Francis Medical center where post graduate trainees and attending physicians were enrolled. A 26-inch-high resolution screen was used and placed at eye level for the endoscopist. We selected 50 high resolution slides of polyps (<1 cm) intermixed with slides of normal colonic mucosa. These slides were downloaded from Orpheus Medical, a global clinical media platform and video informatics company. These were shown to each endoscopist standing either 3, 6, or 9 feet away (0.91, 1.8, or 2.7 meters) from the screen on three separate days, arranged in 3 different configurations. Both the rate of polyp detection and the sizes of polyps measured at various distances were recorded. The endoscopists were able to move +/- 10 cm (0.5 feet) from their index position to enhance their visualization and for better accommodation. The data was collected for multiple outcomes and statistical analysis was performed using odds ratio and t-test. Results Seven subjects who were either 3rd year Gastroenterology fellows or attendings were included in the study. We included 50 slides, with 33 consisting of polyps (<1 cm) and others containing normal colonic mucosa. Our results showed that the number of polyps detected decreased as the distance from the screen increased. Overall polyp detection rate (PDR) was 92.18% at 3 feet (0.91 m), 87% at 6 feet (1.8m) and 77% at 9 feet (2.7m). An endoscopist positioned at 3 ft had a statistically significant higher polyp detection rate than one positioned at 9 ft with odds ratio (OR) of 3.43 (95% CI: 1.45 – 8.11, p= 0.004). The mean polyp size reported by all subjects was 2.68 mm at 3 feet, 2.57 mm at 6 feet and 2.25 mm at 9 feet. Comparison of mean polyp sizes at different distances from screen did not reveal statistically significant differences. Secondary outcomes included accuracy of polyp detection, miss rate and mean overestimation rate. The participating subjects were surveyed verbally at the end of the study to assess their comfort at various distances. They reported the highest level of comfort at 3 feet (0.91m), followed by 6 feet (1.8m). Conclusions This quality improvement study sheds light on the importance of screen distance for polyp detection, especially in case of smaller polyps <1cm. Our results show that ideal screen distance for polyp detection should be close to 3 feet (0.91m) and ideally no more than 6 feet (1.8m). Similarly, our results also point out that polyp size may be overestimated if the examiner is too close to the screen and underestimated if the examiner is too far from the screen. We advocate standardization of screen distance from the endoscopist, so that the polyp size estimation is uniform across the board.