Aizhu Tao

Upper and Lower Tear Menisci in the Diagnosis of Dry Eye

PURPOSE 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. METHODS 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. RESULTS 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. CONCLUSIONS 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.

Diurnal Variation of Upper and Lower Tear Menisci

PURPOSE To determine diurnal variation of tear menisci around upper and lower eyelids in normal subjects. DESIGN Prospective laboratory investigation. METHODS Twenty young healthy Chinese subjects (10 women and 10 men; mean age, 21.3 years; range, 20 to 26 years) with no history of contact lens wear or previously diagnosed dry eye were recruited. A custom-built, real-time anterior segment optical coherence tomography (OCT) instrument was used simultaneously to image the upper and lower tear menisci. Repeated measurements immediately after blinking were conducted on both eyes during a 24-hour period, including immediately before and after sleeping. Dimensional information of the tear menisci were obtained from the OCT images using custom software. RESULTS There were no significant differences between right and left menisci, nor were there any differences between females and males in the lower tear meniscus (P > .05, repeated-measurement analysis of variance [ANOVA]). Although the lower tear meniscus variables were correlated strongly with upper meniscus variables, the lower meniscus was significantly greater than the upper one. Significant diurnal variations (P < .05, repeated-measurement ANOVA) of all measured variables were observed during the study period. Tear menisci were significantly increased at eye opening after overnight sleep compared with the baseline before sleep at 10 pm (P < .001, post hoc tests). They remained elevated up to 10 minutes after eye opening (P < .001, post hoc tests). CONCLUSIONS Real-time OCT can provide useful information regarding the dynamics of the tear system. Diurnal variation of the upper and lower tear menisci occur.

The role of axial resolution of optical coherence tomography on the measurement of corneal and epithelial thicknesses

PURPOSE Our purpose was to investigate the role of the axial resolution of optical coherence tomography (OCT) on the measurement of corneal and epithelial thickness by evaluating the repeatability and agreement among different 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 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 coefficient of repeatability 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.

Corneal biomechanical properties and intraocular pressure in high myopic anisometropia.

Objectives: To investigate corneal biomechanical properties and intraocular pressure (IOP) in patients with high myopic anisometropia. Methods: Patients with high myopic anisometropia (n = 23) and emmetropic subjects (n = 55) were enrolled. Corneal hysteresis (CH), Goldmann-correlated intraocular pressure (IOPg), corneal resistance factor, and corneal-compensated IOP (IOPcc) were measured with Ocular Response Analyzer. Central corneal thickness was measured by optical coherence tomography. Zeiss IOL-Master determined the values of corneal refractive power and ocular axial length. Results: Significant differences were presented in CH, IOPg, and IOPcc among the high myopic, contralateral, and normal eyes (analysis of variance, P<0.05). CH in high myopic eye was lower than that in the other two groups (post hoc, P<0.05), whereas IOPg and IOPcc in both eyes of anisometropic myopia were higher compared with the normal subjects (post hoc, P<0.01). CH was associated with central corneal thickness and axial length in high myopic eyes. All measured biometric parameters showed significant correlations between two eyes in high myopic anisometropia. Conclusions: High myopic eyes showed decreased CH, but not corneal resistance factor, which indicates that some aspects of corneal biomechanical properties may be altered in high myopic eye of anisometropia. It is also suggested that anisometropic eyes with different refractive errors do not share the same biomechanical properties, which may impact IOP measurement.

Clinical significance of tear menisci in dry eye.

Purpose: To determine the relationships among tear menisci variables and clinical tests used in the diagnosis of dry eye patients. Methods: Dry eye patients (n=50; age, 35.2 years) and healthy subjects (n=48; age, 33.3 years) were recruited. Upper and lower tear menisci were imaged noninvasively by optical coherence tomography (OCT) immediately after normal and delayed blinking in both eyes. Tear meniscus heights, areas, and radius of curvatures were obtained by custom software. Tear film break-up time was measured by fluorescein (fluorescein film tear break-up time, FTBUT) and tearscope (noninvasive tear film break-up time), ocular surface vital staining was evaluated with fluorescein (FS), and secretion was measured by Schirmer I test without and with anesthesia. Results: In dry eye patients, all lower tear meniscus variables during normal blinking were correlated with all clinical tests except Schirmer I test without anesthesia. Upper tear meniscus variables were correlated with FTBUT and Schirmer I test with anesthesia. During delayed blinking, upper and lower tear menisci variables were correlated with Schirmer I test without anesthesia and FS; however, there were no correlations between menisci variables and FTBUT or Schirmer I test with anesthesia. In healthy subjects, only lower meniscus variables were correlated with Schirmer I test with anesthesia during normal blinking. During delayed blinking, the lower meniscus variables were correlated with only the Schirmer I test without anesthesia. Conclusions: Lower tear menisci were correlated more strongly with the clinical tests than were upper menisci. The tear menisci were associated with the basic tear secretion during normal blinking. Delayed blinking may affect reflex tearing levels.

Ocular Anterior Segment Biometry and High-Order Wavefront Aberrations During Accommodation

PURPOSE We investigated the relationships between the ocular anterior segment biometry and the ocular high-order aberrations (HOAs) during accommodation by combined ultralong scan depth optical coherence tomography (UL-OCT) and wavefront sensor. METHODS We enrolled 35 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 diopters [D]). 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 nonaccommodative and accommodative states were compared, and the relationships between them were investigated. RESULTS Compared to the nonaccommodative 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 nonaccommodative and accommodative conditions, HORMS for a fixed pupil size was correlated negatively with pupil diameter (r = -0.532 and -0.801, respectively, P < 0.01). CONCLUSIONS The anterior segment biometry and the HOAs changed significantly during accommodation. The increase in HOAs mainly was due to the increased convexity of the anterior surface of the lens during accommodation. Contraction of the pupil may help to decrease HOAs.

Intraocular Pressure and Calculated Diastolic Ocular Perfusion Pressure during Three Simulated Steps of Phacoemulsification In Vivo

PURPOSE To investigate the fluctuations of directly measured intraocular pressure (IOP) and induced diastolic ocular perfusion pressure (DOPP) during three simulated steps of phacoemulsification in vivo. METHODS Twenty-five eyes of 25 patients who underwent phacoemulsification were evaluated. A pressure transducer was inserted into the anterior chamber to measure IOP directly. The cortical cleanup and viscoelastic removal, nuclear disassembly, and anterior capsular polishing stages of phacoemulsification were simulated. Baseline, static, and dynamic IOP measurements at each stage were conducted before a routine phacoemulsification procedure was performed. DOPP was determined as the difference between diastolic blood pressure and IOP. RESULTS The directly measured IOP fluctuated from 13 +/- 4.7 to 96 +/- 6.2 mm Hg during the simulated steps of phacoemulsification (repeated-measurement ANOVA, P < 0.001). It was elevated more than 39 mm Hg compared with the baseline in static and dynamic measurements (post hoc, P < 0.001). Static DOPPs were lower than 0 mm Hg in all cases during simulated cortical cleanup and viscoelastic removal and in 19 cases during simulated nuclear disassembly. Dynamic DOPPs were lower than 0 mm Hg in 14 cases during simulated cortical cleanup and viscoelastic removal. CONCLUSIONS IOP and DOPP fluctuate widely during simulated steps of phacoemulsification. Further studies may be needed to establish the effect of the transient fluctuations in DOPP on visual function.

Automatic segmentation of the central epithelium imaged with three optical coherence tomography devices.

Purpose: The aim of this study was to investigate the feasibility of automatic segmentation of the central corneal thickness (CCT) and epithelial thickness (ET) of the human cornea obtained with different spectral domain optical coherence tomography (OCT) instruments. Methods: Ten left eyes from 10 healthy subjects with a mean age of 22.5±1.5 years participated in this study. A custom-built ultra–high resolution OCT (UHR-OCT) with a 3-&mgr;m axial resolution, ultralong scan depth OCT (UL-OCT) with a 7.5-&mgr;m resolution, and commercial RTVue OCT with a 5-&mgr;m resolution were used to image the cornea. An automated segmentation algorithm was developed to process the OCT images and yield the CCT and ET. The measurement was verified by a manual measurement. Results: The automatic algorithm successfully processed the central thickness of the cornea and corneal epithelium for all images. The average CCT obtained by the automatic segmentation algorithm was 528.1±22.4 &mgr;m, 526.1±23.4 &mgr;m, and 525.2±23.7 &mgr;m for UHR-OCT, UL-OCT, and RTVue, respectively. The average ET was 53.2±2.0 &mgr;m, 54.1±3.0 &mgr;m, and 52.1±2.5 &mgr;m for UHR-OCT, UL-OCT, and RTVue, respectively. These measurements were in agreement with those of the manual method for the CCT (all r>0.997, P<0.05) and for the ET (all r>0.71, P<0.05). Conclusions: The algorithm seemed to be feasible for automatically segmenting the CCT and ET in OCT images using these tested OCT devices. The segmented results were equivalent to that obtained with the manual method.

Phacoemulsification Induced Transient Swelling of Corneal Descemet’s Endothelium Complex Imaged with Ultra-High Resolution Optical Coherence Tomography

Purpose Thickness changes of corneal sub-layers after phacoemulsification were investigated by spectral domain ultra-high resolution optical coherence tomography (UHR-OCT). Methods The corneas (n = 26) of 26 age-related cataract surgery patients were studied. UHR-OCT was used to evaluate the thickness of Descemet’s Endothelium Complex (DEC), stroma, Bowman’s layer, epithelium, and full cornea at the center (CCT) before, one day after, and one week after surgery. Non-contact specular microscopy measured CCT, endothelial cell density, and morphology. Results The DEC, stroma, Bowman’s layer, and epithelium were visualized by UHR-OCT. Before surgery, the DEC in all cases appeared as a translucent space between two smooth opaque lines. One day after surgery, the posterior corneal surfaces in half of the eyes were wavy and irregular. Compared to the baseline, one day after surgery the thickness increases of the DEC, stroma, and CCT were 4.3 ± 2.6 µm, 25.5 ± 24.9 µm, and 32.1 ± 26.6 µm, respectively (P < 0.001). The morphology of the DEC and the CCT recovered to baseline one week after surgery (P > 0.05), but endothelial cell density was 8.7% less than at baseline. There were no significant changes in Bowman’s layer and epithelium after the operation. The pre-operative DEC thickness was positively correlated with the decreased endothelial cell density at 1 day after surgery (r = 0.55, P = 0.003). Conclusions The DEC showed edematous thickening and different degrees of morphological changes after phacoemulsification. The DEC deformation and corneal edema recovered by one week after surgery, which indicated recovery of endothelial function. UHR-OCT is a useful tool to evaluate function of the DEC after phacoemulsification. Pre-operative DEC thickness may indicate the integrity of the endothelium and could be used for predicting endothelial cell loss after phacoemulsification.

Upper and lower tear menisci after laser in situ keratomileusis.

Objectives To determine upper and lower tear menisci using optical coherence tomography (OCT) in volunteers after laser in situ keratomileusis (LASIK) for myopia. Methods Thirty-five eyes of 35 nonsurgical volunteers were evaluated. Twenty-eight eyes of 28 volunteers who underwent LASIK served as the study group. The height, area, and volume of the upper and lower tear menisci were obtained in the study group, using OCT before surgery, 1 week, 1 month, and 20 months after surgery. At each visit, Schirmer test (type I, without anesthesia), tear break-up time, and corneal fluorescein staining score were evaluated. OCT imaging was conducted in the nonsurgical group with the same settings. Results The lower tear meniscus volume at baseline were significantly smaller in the study group compared with the nonsurgical group (t test, P < 0.01). The upper tear meniscus volume decreased from 0.44 ± 0.11 μL to 0.37 ± 0.08 μL at 1 month after surgery (P < 0.05). The lower tear meniscus volume (0.54 ± 0.15 μL) reduced to 0.44 ± 0.10 μL at 1 month after surgery (posthoc, P < 0.05). For the subgroup analysis, tear menisci, Schirmer test, and tear break-up time after LASIK decreased during the first 1 month (P < 0.05) and recovered by 20 months after surgery (t test, P > 0.05). Conclusions The upper and lower tear menisci decreased up to 1 month after LASIK and recovered by 20 months. OCT is a useful tool for evaluating the tear system in a noninvasive manner.