Yimin Yuan

Wenzhou University, Yung-chia, Zhejiang Sheng, China

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Publications (13)27.38 Total impact

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    ABSTRACT: To investigate changes of corneal thickness at the vertical and horizontal meridians and of wavefront aberrations (WA) over a 30-day period of overnight myopia orthokeratology (OK) lens wear. Sixteen subjects (11 women, 5 men, 26.3±3.2 years) were enrolled and fitted for OK lenses. Long scan depth optical coherence tomography was used to measure corneal thickness profiles at both horizontal and vertical meridians at baseline and on days 1, 7, and 30 days. Corneal and ocular WA of a 6-mm pupil were measured and the root-mean-square (RMS) of the astigmatism, coma, spherical aberration (SA), and total higher-order aberrations (HOAs) were determined. During the 30-day period, the central cornea thinned in the horizontal and vertical meridians, whereas corneal thickening occurred in the temporal, nasal, and inferior mid-peripheries. In contrast, the cornea thinned in the mid-peripheral superior. There were significant increases in RMS for astigmatism, SA, coma, and positive horizontal coma during the study period. After OK, there were significant positive correlations between the midperipheral-central thickness change difference and the changes in corneal and ocular RMS of total HOAs and SA (r range: 0.281 to 0.492, P<0.05). Only the change of corneal coma RMS was correlated with midperipheral-central thickness change difference (r=0.270, P<0.05). The change in corneal horizontal coma was correlated with the temporal-nasal thickness change difference (r=-0.289, P<0.05). Overnight OK caused unique changes in corneal thickness profiles at the vertical and horizontal meridians and increased corneal and ocular HOAs related to corneal reshaping.
    Eye & contact lens 03/2014;
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    ABSTRACT: To determine the biometry of anterior segment dimensions of the human eye on both horizontal and vertical meridians with extended scan depth optical coherence tomography (OCT) during accommodation.
    PLoS ONE 01/2014; 9(8):e104775. · 3.73 Impact Factor
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    ABSTRACT: Purpose: To investigate the relationships between the ocular anterior segment biometry and the ocular high-order aberrations (HOAs) during accommodation by combined ultra-long scan depth optical coherence tomography (UL-OCT) and wavefront sensor. Methods: Thirty-five right eyes of young healthy subjects (21 women and 14 men; age: 25.6 ± 3.1 years; spherical equivalent refractive error: -0.41 ± 0.59 D) were enrolled. A custom-built UL-OCT and a wavefront sensor were combined. They were able to image the ocular anterior segment and to measure the HOAs during accommodation. The differences in the biometric dimensions and in the HOAs between the non-accommodative and accommodative states were compared, and the relationships between them were investigated. Results: Compared to the non-accommodative condition, anterior chamber depth, pupil diameter, and radii of the crystalline lens surface curvatures decreased significantly, while the lens thickness and root-mean-square of high-order aberration (HORMS) of fixed 3-mm pupil size increased under the accommodative stimulus (P < 0.01). A negative correlation was found between the change in the radius of the lens anterior surface curvature and the change in HORMS (r = -0.370, P = 0.014). For both non-accommodative and accommodative conditions, HORMS for a fixed pupil size was negatively correlated with pupil diameter (r = -0.532 and -0.801, respectively, P < 0.01). Conclusions: Both the anterior segment biometry and the HOAs changed significantly during accommodation. The increase in HOAs was mainly due to the increased convexity of the anterior surface of the lens during accommodation. Contraction of the pupil may help to decrease HOAs.
    Investigative ophthalmology & visual science 09/2013; · 3.43 Impact Factor
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    ABSTRACT: In order to understand the relationship between accommodation and vision quality, a custom-built ultra-long scan depth spectral domain optical coherence tomography (UL-SDOCT) and a Shack-Hartmann wavefront sensor (HSWFS) were combined. The resolution and scan depth of UL-SDOCT are 6 μm and 15.6 mm, respectively, which allow for high-resolution imaging of the whole anterior segment. The HSWFS consists of a 32×32 microlens array, and is able to measure first 35th-order Zernike aberrations with (1/20)λ measurement accuracy. The integrated system succeeded in measuring the ocular anterior segment dimension parameters and the ocular monochromatic high-order aberrations simultaneously under the conditions of nonaccommodative and accommodative stimuli. This may help understand the regulatory mechanism of image quality control in the human eye.
    Journal of Biomedical Optics 12/2012; 17(12):120501. · 2.88 Impact Factor
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    ABSTRACT: PURPOSE: Our purpose was to investigate the role of the axial resolution of optical coherence tomography on the measurement of corneal and epithelial thickness by evaluating the repeatability and agreement among different optical coherence tomography (OCT) devices with different axial resolutions. METHODS: Twenty right eyes of 20 healthy subjects (age: 22.3 ± 1.3 years) and 18 eyes of 18 patients (age: 25.7 ± 6.8 years) after laser in situ keratomileusis (LASIK) refractive surgery were tested. Each subject was imaged using four OCT devices: ultra-high resolution OCT (UHR-OCT), ultra-long scan depth OCT (UL-OCT), commercial RTVue and Visante. The OCT images obtained from UHR-OCT, UL-OCT and RTVue were processed with a custom automated algorithm for measuring the central corneal thickness (CCT) and central epithelial thickness (ET). CCT measurements from pachymetry maps that were generated by RTVue and Visante were also obtained. Results: For both groups, the CCT and ET measured by UHR-OCT and UL-OCT were highly correlated with RTVue when the automated image processing algorithm was used. The CCT measurements from the RTVue and Visante pachymetry were thicker than those measurements obtained from the automatic algorithm. The coefficient of repeatability (CoR) was less than 4.9 µm in the healthy subjects and 7.9 µm in the LASIK patients, and the associated intraclass correlation coefficient (ICC) was greater than 0.992 in both groups for the CCT measurements. For the ET measurements using UHR-OCT, UL-OCT and RTVue, the CoR was less than 2.2 µm in the healthy subjects and 4.8 µm in the LASIK patients with an ICC that was greater than 0.84. CONCLUSIONS: The axial resolution of OCT may play a role in determining the precision with which the CCT and the ET can be measured, although it may not affect the measurement of results.
    Investigative ophthalmology & visual science 11/2012; · 3.43 Impact Factor
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    ABSTRACT: To visualize the precorneal tear film (PCTF) in dry eye patients using ultrahigh resolution optical coherence tomography (UHR-OCT). A custom-built UHR-OCT with ultrahigh resolution (~3 μm) was used to image the PCTF at the vertical meridian. Eighteen right eyes of 18 previously diagnosed dry eye patients (9 men and 9 women, age, 47.8±20.7 years) with aqueous tear deficiency were studied. Images were taken during normal and delayed blinking. The visualized PCTF was measured directly. An indirect calculation was used to obtain the thickness in cases where the PCTF could not be visualized. During normal blinking, the PCTF was visualized in 5 of 18 eyes (27.8%) with an average PCTF thickness of 5.8 μm (SD, 1.3 μm). During delayed blinking, the PCTF was visualized in 11 eyes (61.1%) with a significantly increased average thickness of 7.3 μm (SD, 0.9 μm; P<0.05). The percent increase of the visualized PCTF thickness was higher during delayed blinking compared with normal blinking (χ test, P<0.05). The averaged PCTF was 4.4 μm during normal blinking, and the PCTF thickness was significantly increased to 6.6 μm (SD, 2.9 μm; P<0.05) during delayed blinking. We report the first visualization of PCTF in vivo in dry eye patients with UHR-OCT. Precorneal tear film can be directly visualized in some eyes during both normal and delayed blinking, and it seemed thicker during delayed blinking compared with normal blinking.
    Eye & contact lens 07/2012; 38(4):240-4.
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    ABSTRACT: The aim was to determine the repeatability of ultralong scan depth spectral-domain optical coherence tomography (SD-OCT) measurements of the ocular anterior segment during accommodation. The center wavelength of the SD-OCT light source was 840 nm with a bandwidth of 50 nm. The ocular axial resolution of the system was approximately 6.0 μm, and the scan depth was 7.2 mm in air. Twenty eyes of 20 healthy subjects were imaged with a custom-built, ultralong scan depth SD-OCT during 2 visits. The anterior segment images were acquired during nonaccommodative and maximal accommodative states. After image processing and correction, the true values of the morphometric dimensions of the anterior eye were obtained. The variables of the two states from two visits were compared. For the corrected anterior segment images, the variables did not significantly differ from one visit to the next. The values of anterior chamber depth, pupil diameter, and the radius of the lens anterior surface curvature during accommodation were significantly smaller than those during the nonaccommodative state. The lens thickness significantly increased with accommodation. There was no significant difference in the posterior surface curvature of the lens between the two states. Ultralong scan depth SD-OCT holds promise for quantifying dimensional changes in the eye during accommodation. The instrument demonstrated good repeatability of ocular anterior segment dimensional measurements during accommodation.
    Eye & contact lens 03/2012; 38(2):102-8.
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    ABSTRACT: To measure vertical and horizontal thickness profiles of the central and peripheral corneal epithelium and determine if daytime changes occur. Forty eyes of 20 normal subjects were imaged by ultrahigh resolution spectral domain optical coherence tomography to profile the corneal epithelial thickness from the edge of Bowman layer to the central cornea across the vertical and horizontal meridians. Measurements were made at 10:00 AM and again at 6 and 8 hours later. The baseline vertical meridional epithelial thickness was thinnest, 42.9 ± 4.1 μm, at the edge of Bowman layer in the superior region. It increased in thickness (P < 0.01), toward the central cornea. The central epithelium averaged 52.5 ± 2.4 μm, becoming thickest, 55.2 ± 2.5 μm, in the inferior pericentral region. It thinned toward the inferior periphery, reaching 51.3 ± 5.1 μm at the edge of Bowman layer (P < 0.01). Along the horizontal meridian, the epithelium was thickest at the nasal side, 58.6 ± 5.1 μm, and temporal side, 59.3 ± 6.6 μm, near the edges of Bowman layer. It thinned toward the central cornea. There were no significant changes in the epithelial thickness at any location over 8 hours. Epithelial thickness varied over the horizontal and vertical meridians and appeared stable during the daytime.
    Cornea 02/2012; 31(9):1036-43. · 1.75 Impact Factor
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    ABSTRACT: An 840-nm wavelength spectral domain optical coherence tomography (SD-OCT) with prolonged scan depth was developed and mounted onto a conventional slit lamp for imaging the anterior segment of the eye. X-Y cross aiming was applied to align the SD-OCT scanning position during imaging. An internal fixation target displayed on a miniature LCD monitor was provided. The SD-OCT instrument had an axial resolution of 6 μm and a prolonged scan depth of 7.2 mm. High-quality SD-OCT images, consisting of 2,048 × 2,048 pixels, were acquired of the entire anterior chamber and entire crystalline lens from a healthy subject. The entire cornea, anterior chamber angle, limbus, and iris were clearly visible. Additionally, the internal structure of crystalline lens, including anterior and posterior surfaces of the crystalline lens, capsule, nucleus, and cortex, were clearly imaged with the instrument. The system was also tested in imaging accommodation of the same eye, demonstrating the feasibility of the novel approach for evaluating presbyopia/accommodation.
    Ophthalmic Surgery Lasers and Imaging 11/2010; 41 Suppl:S65-9. · 1.46 Impact Factor
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    ABSTRACT: To measure the tear meniscus dynamics in aqueous tear deficiency dry eye patients using optical coherence tomography. Clinical research study of a laboratory technique. Twenty-five aqueous tear deficiency dry eye patients and 30 healthy subjects were recruited. Upper and lower tear menisci of 1 randomly selected eye of each participant were imaged during normal and delayed blinking using optical coherence tomography. Measured parameters included upper tear meniscus height and volume, lower tear meniscus height and volume, the blink outcome defined as the meniscus volume change during blink action, and open eye outcome defined as the meniscus volume change during the open eye period. During normal blinking, both tear meniscus height and volume before blink in dry eye patients were significantly smaller than those in healthy subjects, except for the upper tear meniscus volume. During normal blinking, the blink outcome and open eye outcome of lower tear meniscus were significantly smaller in dry eye patients compared with healthy subjects. During delayed blinking, the upper and lower tear menisci heights and volumes significantly increased in both groups. However, dry eye patients had smaller increases than healthy subjects. During delayed blinking, the open eye outcomes of upper and lower tear menisci were smaller in dry eye patients than healthy subjects. Dry eye patients seem to have reduced tear meniscus dynamics during normal blinking and smaller increases of meniscus volume during delayed blinking. Analysis of tear meniscus dynamics may provide more insight in the altered tear system in dry eye patients.
    American journal of ophthalmology 04/2010; 149(6):932-938.e1. · 3.83 Impact Factor
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    ABSTRACT: To demonstrate the capability of directly visualizing the entire ocular surface and the entire contact lens on the eye using spectral domain optical coherence tomography (SD-OCT). A custom-built, high-speed, and high-resolution SD-OCT was developed with extended scan depth and width. The eye was imaged before and after wearing a toric soft contact lens (PureVision; Bausch & Lomb). A lubricant eye drop (Soothe; Bausch & Lomb) was instilled in the eye to enhance the image contrast on the lens. The same toric soft contact lens immersed in the contact lens solution was also imaged with a contrast enhancement medium (0.5% Intralipid). Cross-sectional OCT images of the entire ocular surface were acquired with high-resolution 2,048 x 2,048 pixels. Quantitative surface height map of the ocular surface was obtained from a radial scan data set containing 32 B-scans. With the contrast enhancement agent, the entire toric soft contact lens was clearly visualized, both in vitro and on the eye. The surfaces of the lens were detected and used to generate the thickness maps of the soft contact lens. Spectral domain optical coherence tomography with extended scan depth and width is a promising tool for imaging the entire ocular surface shape and soft contact lenses. This successful demonstration suggests that the extended depth SD-OCT is effective in studying ocular surface shape and its interaction with a soft contact lens. The novel method is helpful for the evaluation of contact lens fitting and lens design.
    Eye & contact lens 03/2010; 36(2):73-6.
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    ABSTRACT: Purpose. To use optical coherence tomography (OCT) to evaluate the effect of punctal occlusion on tear meniscus volume in dry eye patients. Methods. Occlusion of both upper and lower puncta with collagen plugs was performed on one eye each in 20 dry eye patients and 20 normal subjects. The upper and lower tear menisci were imaged simultaneously by real-time OCT before punctal occlusion and on days 1, 4, 7, and 10 afterward. The heights, cross-sectional areas, and volumes of the menisci were obtained. Schirmer I test with anesthesia and tear break-up time (TBUT) testing were also performed. Results. At baseline, both upper and lower tear meniscus heights and volumes in dry eye patients were lower than those in control subjects (P < 0.05). The volume of the lower tear meniscus was 0.28 +/- 0.09 microL in dry eye patients and 0.55 +/- 0.22 microL in control subjects at baseline (P < 0.05). After punctal occlusion, the Schirmer I test scores of dry eye patients did not change (P > 0.05), but the heights and volumes of the upper and lower tear menisci increased (P < 0.05). In control subjects, Schirmer I test scores decreased (P < 0.05), but the heights and volumes of the upper and lower tear menisci did not change (P > 0.05). Conclusions. Punctal occlusion induced increases in the upper and lower tear meniscus volumes in dry eye patients. The absence of change in the tear menisci of control eyes may indicate the presence of an autoregulatory mechanism in the tear system that maintains a balance in the tear volume.
    Investigative ophthalmology & visual science 11/2009; 51(4):1965-9. · 3.43 Impact Factor
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    ABSTRACT: To measure the upper and lower tear menisci in patients with aqueous tear deficiency (ATD) dry eye by real-time optical coherence tomography (OCT) and to determine the most effective meniscus variables for the diagnosis of dry eye. Eyes of 48 pre-screened ATD patients were compared with those of 47 healthy subjects. Upper and lower tear menisci were imaged simultaneously by real-time OCT immediately after blinking. The height, radius, and cross-sectional area of upper and lower tear menisci were obtained. The tear meniscus radius, height, and cross-sectional area were significantly smaller in patients with dry eye than in healthy subjects (P < 0.01). The lower tear meniscus variables were higher than the upper menisci (P < 0.01) in normal subjects; however, no significant differences between menisci were found in ATD patients. In both groups, the upper and lower tear meniscus variables were strongly correlated with each other. Good dry eye diagnostic accuracies were obtained with cutoff values for an abnormal lower tear meniscus radius (LTMR) of 182 microm and a lower tear meniscus height (LTMH) of 164 microm. The LTMR diagnostic sensitivity and specificity were 0.92 and 0.87, respectively. The LTMH diagnostic sensitivity and specificity were 0.92 and 0.90. Upper tear meniscus variables in ATD patients were assessed by real-time OCT. The tear meniscus was smaller in ATD patients than in healthy subjects. LTMR and LTMH may have potential in the diagnosis of ATD.
    Investigative ophthalmology & visual science 02/2009; 50(6):2722-6. · 3.43 Impact Factor

Publication Stats

96 Citations
27.38 Total Impact Points

Institutions

  • 2014
    • Wenzhou University
      Yung-chia, Zhejiang Sheng, China
  • 2009–2013
    • Wenzhou Medical College
      Yung-chia, Zhejiang Sheng, China
  • 2012
    • Zhejiang University
      • School of Medicine
      Hangzhou, Zhejiang Sheng, China