Ce Zheng
National University of Singapore
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Featured researches published by Ce Zheng.
Pattern Recognition | 2007
Juan Xu; Opas Chutatape; Eric Sung; Ce Zheng; Paul Chew Tec Kuan
A deformable-model based approach is presented in this paper for robust detection of optic disk and cup boundaries. Earlier work on disk boundary detection up to now could not effectively solve the problem of vessel occlusion. The method proposed here improves and extends the original snake, which is essentially a deforming-only technique, in two aspects: knowledge-based clustering and smoothing update. The contour deforms to the location with minimum energy, and then self-clusters into two groups, i.e., edge-point group and uncertain-point group, which are finally updated by the combination of both local and global information. The modifications enable the proposed algorithm to become more accurate and robust to blood vessel occlusions, noises, ill-defined edges and fuzzy contour shapes. The comparative results on the 100 testing images show that the proposed method achieves better success rate (94%) when compared to those obtained by GVF-snake (12%) and modified ASM (82%). The proposed method is extended to detect the cup boundary and then extract the disk parameters for clinical application, which is a relatively new task in fundus image processing. The resulted cup-to-disk (C/D) ratio shows good consistency and compatibility when compared with the results from Heidelberg Retina Tomograph (HRT) under clinical validation.
British Journal of Ophthalmology | 2007
Jovina Ls See; Paul Chew; Scott D. Smith; Winifred Nolan; Yiong Huak Chan; David Huang; Ce Zheng; Paul J. Foster; Tin Aung; David S. Friedman
Aim: Using the anterior segment optical coherence tomography (AS-OCT) to quantify changes in anterior segment morphology going from light to dark and following laser iridotomy (LI). Methods: Prospective observational study. 17 consecutive subjects without peripheral anterior synechiae undergoing LI were evaluated using gonioscopy and AS-OCT. Angle configuration including angle opening distance (AOD) at 500 microns anterior to the scleral spur, AOD500, trabecular-iris space area up to 750 microns from the scleral spur, TISA750 and the increase in angle opening going from dark to light conditions was determined. Results: Both mean AOD500 and TISA750 increased nearly threefold going from dark to light. Both also significantly increased following LI (p<0.001) as did gonioscopic grading of the angle in all quadrants (p<0.001, McNemar’s test). Angles were more than twice as wide on average in the dark after LI than before LI (p<0.05). Both the mean absolute change and the mean proportionate change in AOD500 and TISA750 when going from light to dark were greater after LI than before (p<0.05). Conclusion: Increased illumination as well as LI resulted in significant widening of the anterior chamber angle. AS-OCT (which does not require a water bath and can be performed with the patient at the slit lamp) identified similar magnitude changes as those previously reported using ultrasound biomicroscopy (UBM). Furthermore, the angle appears to open more both in absolute terms and and proportionate terms in response to illumination after LI.
Journal of Glaucoma | 2008
Winifred Nolan; Jovina Ls See; Tin Aung; David S. Friedman; Yiong Huak Chan; Scott D. Smith; Ce Zheng; David Huang; Paul J. Foster; Paul Chew
PurposeTo measure changes in angle width after phacoemulsification and intraocular lens (IOL) implantation using anterior segment optical coherence tomography (AS-OCT). Materials and MethodsTwenty-one patients undergoing cataract surgery were recruited from the National University Hospital, Singapore. AS-OCT images were obtained of nasal and temporal angle quadrants before and at 1-month after surgery. Optical measurements of central anterior chamber depth were obtained, and gonioscopic measurement of angle width was recorded. AS-OCT angle width parameters measured in the nasal and temporal quadrants included the angle opening distance at 500 μm (AOD500) anterior to the scleral spur and the trabecular iris surface area at 750 μm (TISA750) anterior to the scleral spur. Preoperative and postoperative measurements were compared using paired samples t tests. ResultsData were collected from 21 eyes of 21 subjects with cataract. Seven subjects also had gonioscopic evidence of primary angle closure. Mean anterior chamber depth increased from 2.92 (±0.54) to 4.24 (±0.57) mm (P=0.044) after cataract extraction. There was a significant increase in AS-OCT parameters for both nasal and temporal angles after surgery. An 88.2% increase in AOD500 was measured for the nasal angle quadrant with a mean difference of 213.9 (±173) μm (P<0.001). TISA750 increased by 94.4% in the nasal angle with a mean difference of 0.134 (±0.104) μm2 (P<0.001). ConclusionsAS-OCT imaging demonstrates increases in angle width after cataract extraction.
British Journal of Ophthalmology | 2011
Carol Y. Cheung; Ce Zheng; Ching-Lin Ho; Tin A. Tun; Rajesh S. Kumar; Fouad El Sayyad; Tien Yin Wong; Tin Aung
Objective To propose the Schwalbe line (SL) as a new anatomical landmark, independent of the scleral spur (SS) location, for assessing anterior chamber angle (ACA) width quantitatively with high-definition optical coherence tomography (HD-OCT). Methods Study subjects underwent dark-room gonioscopy and HD-OCT in one randomly selected eye. The authors developed a computer-aided program to define two new quantitative parameters for assessing ACA width: Schwalbe line-angle opening distance (SL-AOD) measured at the SL, and Schwalbe line-trabecular–iris space area (SL-TISA) measured 500 μm from the SL. The associations between SL parameters, SS parameters and gonioscopic grading were evaluated. Results Seventy-three (47 females, 26 males) subjects were recruited, the majority of whom were Chinese (89%). The authors excluded 29 images (19.9%) owing to poor image quality, leaving 117 HD-OCT images (65 nasal, 52 temporal) for analysis. SL and SS could be identified in 95% and 85% of quadrants respectively (p=0.035). SL-AOD and SL-TISA were significantly correlated with SS parameters (all r≥0.85) and gonioscopic grading (all r≥0.69). In eyes with closed angles (n=36), SL parameters showed strong correlations with gonioscopic grading (r ranged from 0.43 to 0.44). Conclusions Novel angle parameters, based on SL as a landmark, may be useful to quantify ACA width and to assess for risk of angle closure.
British Journal of Ophthalmology | 2008
Daniel Hw Su; David S. Friedman; Jovina Ls See; Paul Tk Chew; Yiong Huak Chan; Winnifred P Nolan; Scott D. Smith; David Huang; Ce Zheng; Yan Li; Paul J. Foster; Tin Aung
Aims: To evaluate the relationship between angle width as determined by anterior segment optical coherence tomography (AS-OCT) and the presence of peripheral anterior synechiae (PAS). Methods: This was a prospective observational case series in which 203 subjects with primary angle closure or open angles were recruited. Images of the nasal, temporal and inferior angles were obtained with AS-OCT in dark conditions. Subjects then underwent gonioscopy by an independent examiner who was masked to the AS-OCT findings. PAS were identified by gonioscopy and defined as abnormal adhesions of the iris to the angle that were at least half a clock hour in width and present to the level of the anterior trabecular meshwork or higher. The total clock hours of PAS were recorded. Results: Sixty-eight subjects (33.5%) were PACS, 76 subjects (37.4%) had PAC/PACG, 14 (6.9%) had primary open angle glaucoma, and 45 (22.2%) subjects were normal with open angles. There was a weak but significant correlation between the angle opening distance (AOD), trabecular iris space area (TISA) and angle recess area (ARA) with clock hours of PAS (Spearman’s correlation coefficients = −0.30, −0.32 and −0.32, respectively, p<0.001). The mean values of the AOD, TISA and ARA in the nasal, temporal and inferior quadrants were significantly less in eyes with PAS compared with those without (p<0.001, Mann–Whitney U test). Analysis by quadrant showed that these parameters were smaller in the nasal and temporal quadrants in eyes with PAS (p<0.01). Conclusions: Angle width determined by AS-OCT and the extent of PAS were weakly correlated, and angle width was significantly smaller in eyes with PAS.
Investigative Ophthalmology & Visual Science | 2013
Arun Narayanaswamy; Ce Zheng; Shamira A. Perera; Hla Myint Htoon; David S. Friedman; Tin A. Tun; Mingguang He; Mani Baskaran; Tin Aung
PURPOSE To compare the changes in iris volume with pupil dilation using anterior segment optical coherence tomography (AS-OCT) in eyes of subjects with different subtypes of primary angle closure. METHODS This prospective study examined 44 fellow eyes (FA group) of subjects with previous acute primary angle closure (APAC), and 56 subjects (AC group) with chronic primary angle closure and/or primary angle closure glaucoma. All participants underwent gonioscopy and AS-OCT imaging. The iris volume, iris cross-sectional area, and pupil diameter were measured with custom semiautomated software. The main outcome variable analyzed was mean change in iris volume between light and dark conditions in a multivariate linear regression analysis. RESULTS Thirty-five eyes from the FA group (79.5%) and 50 eyes from the AC group (89.3%) were included in the final analysis. When going from light to dark, iris volume did not change significantly in eyes in the FA group (+1.50 ± 6.73 mm(3); P = 0.19), but decreased in the AC group by 1.52 ± 3.07 mm(3) (P < 0.001). This difference was significant (P = 0.01). On multivariate analysis after controlling for age, sex, baseline pupil diameter, and change in pupil diameter, age (β = -0.397; P < 0.001) and diagnostic category (AC versus FA group; β = 0.347; P < 0.001) were significant determinants of iris volume change. CONCLUSIONS With physiologic mydriasis, the iris volume decreased in eyes with chronic angle closure but remained unchanged in fellow eyes of APAC. Such variations in iris volume responses may influence the subtype of angle closure that develops.
British Journal of Ophthalmology | 2011
Boey Py; Arun Narayanaswamy; Ce Zheng; Shamira A. Perera; Hla Myint Htoon; Tin A. Tun; Steve K. L. Seah; Tina T. Wong; Tin Aung
Objective To analyse blebs of phacotrabeculectomies performed with Ologen collagen implants (ProTop & MediKing, Taipei, Taiwan) and to compare these with blebs of mitomycin C (MMC)–augmented phacotrabeculectomies. Methods 33 participants underwent phacotrabeculectomy with Ologen implants, and 33 controls underwent phacotrabeculectomy with MMC. Blebs were analysed for height and area using anterior segment optical coherence tomography (ASOCT) at 30, 60 and 90 days after surgery and were also graded clinically with the Moorfields bleb grading system (MBGS) 60 days after surgery. Results With ASOCT, there was no difference in mean bleb height at 30 and 60 days, but at 90 days, bleb height was lower in the Ologen group (Ologen vs MMC, 0.74±0.20 vs 1.00±0.28 mm, p<0.001). There was no difference in mean bleb area at 30, 60 or 90 days. Mean reduction in intraocular pressure at 90 days was greater in the MMC group (Ologen vs MMC, 2.18±4.93 vs 8.00 ±7.60 mm Hg, p<0.001). At 90 days, the Ologen implants were visible in ASOCT images in 13 (39.4%) of 33 participants. With the Moorfields bleb grading system at 60 days, there was no difference in maximal bleb area score between the groups, but bleb height score was lower (Ologen vs MMC, 1.53±0.51 vs 1.81±0.59, p=0.05) and central bleb vascularity score was higher in the Ologen group (3.88±0.55 vs 2.91±0.59, p<0.001). Conclusions Within 3 months of surgery, mean bleb height was lower in the Ologen blebs compared with the MMC blebs. The Ologen implants had not degraded in a third of eyes.
Journal of Glaucoma | 2012
Chelvin C.A. Sng; Mandeep Singh; Paul Chew; Cheryl Ngo; Ce Zheng; Tin A. Tun; Jovina Ls See; Marcus Ang; Seng Chee Loon; Tin Aung
PurposeTo quantify changes in bleb morphology after laser suture lysis (LSL) using anterior segment optical coherence tomography (AS-OCT). Patients and MethodsThis was a prospective observational case series of patients who underwent trabeculectomy surgery with mitomycin-C and required subsequent LSL. Subjects were assessed before and immediately after LSL, and at 3 months after LSL. At each visit, a standardized cross-sectional AS-OCT image of the bleb was obtained, from which a masked observer measured bleb height (hB), cavity height (hC), wall cross sectional area (AW), cavity cross sectional area (AC), and bleb cross sectional area (AB) using custom software. ResultsTwenty-five subjects (25 eyes) were examined. LSL was performed at a mean of 21.5±16.3 days after trabeculectomy. Immediately after LSL, there was a significant increase in mean hB (P=0.026) and mean hC (P=0.45) from pre-LSL. At 3 months after LSL, there was a significant increase in mean hB (P=0.003), mean AC (P=0.047), and mean AB (P=0.006) as compared with before LSL. Increase in hB and hC immediately after LSL was predictive of outcome at month 3. ConclusionsAS-OCT was able to quantify changes in bleb morphology after LSL, some of which were predictive of eventual outcome.
Investigative Ophthalmology & Visual Science | 2012
Ce Zheng; Carol Y. Cheung; Tin Aung; Arun Narayanaswamy; Sim Heng Ong; David S. Friedman; John Carson Allen; Mani Baskaran; Paul Chew; Shamira A. Perera
PURPOSE To evaluate the acceleration of pupil constriction (APC) in response to illumination using video anterior segment optical coherence tomography (AS-OCT) in angle closure and normal eyes. METHODS This was an observational study of 342 Chinese subjects. Iris and angle changes in response to illumination were captured with real-time video recordings of AS-OCT and analyzed frame by frame. APC was calculated using a quadratic function, fitting pupil diameter to a time series. APC was divided into two vector components: acceleration of pupil block (APB) acting perpendicular to the lens surface and acceleration of iris stretch (AIS) acting toward the iris root. RESULTS Of 342 eligible patients, 306 (89.5%) were available for analysis; of whom 136 (41.7%) had angle closure. After adjusting for age, sex, baseline pupil diameter, and iris thickness, APC was significantly lower in angle closure eyes (0.61 mm/s(2)) than in open-angle eyes (0.90 mm/s(2)) (P < 0.0001) as was AIS (0.58 mm/s(2) vs. 0.89 mm/s(2)) (P < 0.001). APB was significantly higher in angle closure eyes compared to open-angle eyes (0.14 mm/s(2) vs. 0.09 mm/s(2)) (P < 0.001). After adjusting for age and sex in logistic regression, the magnitude and direction of all vector parameters were significantly associated with presence of angle closure. CONCLUSIONS Angle closure eyes have smaller AIS and larger APB in response to illumination as measured using AS-OCT videography. This shows that, comparatively, the iris of angle closure eyes stretches less and develops a more convex configuration in response to illumination.
Ophthalmology | 2012
Arun Narayanaswamy; Kelvin Y. Lee; Ma Zhen; Jocelyn Chua; Shu Ming Chai; Pui Yi Boey; Ce Zheng; Tin Aung; Subramanian Venkatraman; Tina Tzee Ling Wong
PURPOSE To determine the efficacy of a subconjunctival injection of hyaluronic acid (HA) with 5-fluorouracil (5FU) formulation as an adjunct in reviving bleb function by needling. DESIGN Prospective, randomized, controlled trial. PARTICIPANTS Fifty patients with previous trabeculectomy and scheduled by the managing physician for a needling intervention. METHODS One eye of each patient was randomized to receive needling with HA-5FU mixture or needling with subconjunctival injection of 5FU solution alone. MAIN OUTCOME MEASURES The primary outcome was the percentage of subjects with an intraocular pressure (IOP) <15 mmHg without any medications at 3 months. Secondary outcomes included the need for additional needling procedures and changes in bleb morphology. RESULTS Forty-nine subjects (25 in the HA-5FU group and 24 in the 5FU group) completed 3 months of follow-up. At baseline, there was no significant difference between the groups in terms of demographic features, subtype of glaucoma, vertical cup-to-disc ratio, or visual field indices. The mean number of glaucoma medications at baseline was higher in the 5FU group (0.8±1.1 [mean ± standard deviation] vs. 0.2±0.6, P = 0.04). An IOP <15 mmHg without medications was reached in 48.0% of subjects in the HA-5FU group and in 33.3% of subjects in the 5FU group (P = 0.2). At 3 months, both groups demonstrated a significant decrease in IOP from baseline (HA-5FU: decrease of 5.9 mmHg [95% confidence interval, 3.4-8.4]; 5FU: decrease of 6.0 mmHg [95% confidence interval, 3.2-8.2]; P<0.001 for both). Intergroup comparisons for IOP change from baseline was not significant (P = 0.9). However, repeat needling was required more frequently in the 5FU group compared with the HA-5FU group (50.0% vs. 12.0%; P = 0.004). There were no significant differences in the number of reported adverse events, bleb vascularity, or morphology between the 2 groups. CONCLUSIONS Subconjunctival injection of HA-5FU to revive bleb function after bleb needling is as effective as 5FU solution. Fewer repeat needlings were required after treatment with HA-5FU, suggesting that the use of a combined formulation of HA-5FU may improve the overall outcomes of bleb needlings.