| PurposeTo measure by ultra-long scan depth optical coherence tomography (UL-OCT) dimensional changes in the anterior segment of human eyes during accommodation.MethodsUtilizing a fiber-based Michelson interferometer, the UL-OCT system was constructed with a superluminescent diode laser-based light source with center wavelength of 840 nm and full-width at half maximum bandwidth of 50 nm. An alternative placement of the zero-delay line on the top and bottom in the reference arm was specially designed to acquire multiple images in one scan. Image enhancement was realized by overlapping the two acquired images. This method was used to compensate the drop of signal-to-noise ratio through the entire image depth. The light was focused on the anterior segment, and the total exposure power at the surface of the cornea was 1.10 mW. The scan speed was set to 4,000 A-scans/sec, a limitation imposed by the charged-couple device (CCD) line scan camera. The scan depth of the system was 12.055 mm. The resolution of the UL-OCT system was measured as 11.Oμm axially and approximately 20μm transversely for 2,048 pixels in the eye.UL-OCT was used to image the cornea to the back surface of the crystalline lens. 41 right eyes of healthy subjects with a mean age of 33.5±6.9 years (range,22-41 years) and a mean refraction of-2.5±2.6 diopters (D) (range,+0.50D～-7.00D)were imaged in two repeated measurements at minimal and maximal accommodation. Custom software corrected the optical distortion of the images and yielded the measurements. The dimensional results included central corneal thickness (CCT), anterior chamber depth and width (ACD, ACW), pupil diameter (PD), horizontal radii of the lens anterior and posterior surface curvatures (LAC, LPC), lens thickness (LT), lens central position (LCP) and anterior segment length (ASL).Statistical Procedures for the Social Sciences 16.0 was used for descriptive statistics and data analysis. All data were presented as means±standard deviations. Paired t-tests were for comparisons between repeated measures of the same accommodative state and between the two different accommodative states. Coefficient of repeatability (COR) and the intraclass correlation coefficient (ICC) were calculated to evaluate the repeatability and reliability.ResultsFor all anterior segment dimensions, there were no significant differences between the two repeated measurements of the same accommodative state (paired t-tests, all p-values> 0.05). The average of the two measurements for each accommodative state was used to determine if there were differences between two states. The CORs for CCT, ACW, ACD, LT, LCP, and ASL were excellent, ranging from 1.23% to 3.59% in the minimal and maximal accommodative states. The CORs for PD were relatively high, 18.90% and 21.63% in minimal and maximal accommodative states respectively. The CORs for LAC and LPC ranged from 34.86% to 42.70% in both accommodative states. The ICCs for CCT, ACD, LT, LCP, and ASL were very high, varying between 0.969 and 0.998. They were slightly lower for PD and ACW,0.874 to 0.925, and showed moderate and fair reliability for LAC and LPC (0.251 to 0.669). Compared to minimal accommodation, PD, ACD, LAC, LPC and LCP decreased and LT and ASL increased significantly at maximal accommodation (P< 0.01), while CCT and ACW did not change (P= 0.0602,0.8345) ConclusionsUL-OCT system successfully imaged accommodative change of the whole anterior segment from the cornea to the back surface of the crystalline lens in vivo. UL-OCT measured changes in anterior segment dimensions during accommodation with good repeatability and reliability. During accommodation, the anterior and posterior surface of the crystalline lens became steeper as the lens moved forward, with decrease of the anterior chamber depth and constriction of the pupil. |
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