Scan Depth Optical Coherence Tomography Research Articles

Anterior Segment Biometry with Phenylephrine and Tropicamide during Accommodation Imaged with Ultralong Scan Depth Optical Coherence Tomography.

Purpose To investigate the influence of phenylephrine and tropicamide on anterior segment biometry with ultralong scan depth optical coherence tomography (UL-OCT) during accommodation. Methods In this study, 20 left eyes of healthy volunteers with a mean ± standard deviation age of 31.05 ± 5.84 years and a mean refraction of −1.16 ± 1.11 diopters (range 0∼−3.0 D) were imaged using UL-OCT after instillation of artificial tears, phenylephrine, and tropicamide in three follow-up trials, respectively. At each follow-up trial, two repeated measurements were performed at states of relax and 5D accommodative stimulation. The dimensional parameters included central corneal thickness (CCT), anterior chamber depth (ACD), pupil diameter (PD), lens thickness (LT), and horizontal radii of the lens anterior and posterior surface curvatures (LAC and LPC). Results Tropicamide led to larger pupil, deeper ACD, thinner LT, and flatter crystalline lens surface (P < 0.05). Phenylephrine induced an increase in PD (P < 0.05), while no significant changes were seen in ACD, LT, LAC, and LPC (P > 0.05). CCT did not change after both phenylephrine and tropicamide instillation in this study (P > 0.05). Tropicamide induced the loss of accommodation and phenylephrine achieved pupil dilation without affecting the accommodation. PD, ACD decreased, LT increased significantly and the anterior and posterior surface of the lens in a 6.294 mm of diameter optical zone became steeper during accommodation after administration of phenylephrine (P < 0.05). Conclusion The anterior segment physiology changed after tropicamide instillation. Besides, tropicamide induced the loss of accommodation and phenylephrine preserved the accommodation with a larger pupil. And, the anterior and posterior surface of lens in a 6.294 mm of diameter optical zone became steeper during the accommodation.

Long scan depth optical coherence tomography on imaging accommodation: impact of enhanced axial resolution, signal-to-noise ratio and speed

BackgroundSpectral domain optical coherence tomography (SD-OCT) was a useful tool to study accommodation in human eye, but the maximum image depth is limited due to the decreased signal-to-noise ratio (SNR). In this study, improving optical resolutions, speeds and the SNR were achieved by custom built SD-OCT, and the evaluation of the impact of the improvement during accommodation was investigated.MethodsThree systems with different spectrometer designs, including two Charge Coupled Device (CCD) cameras and one Complementary Metal-Oxide-Semiconductor Transistor (CMOS) camera, were tested. We measured the point spread functions of a mirror at different positions to obtain the axial resolution and the SNR of three OCT systems powered with a light source with a 50 nm bandwidth, centered at a wavelength of 840 nm. Two normal subjects, aged 26 and 47, respectively, and one 75-year-old patient with an intraocular lens implanted were imaged.ResultsThe results indicated that spectrometers using cameras with 4096 camera pixels optimized the axial resolutions, due to the use of the full spectrum provided by the light source. The CCD camera system with 4096 pixels had the highest SNR and the best image quality. The system with the CMOS camera with 4096 pixels had the highest speed but had a compromised SNR compared to the CCD camera with 4096 pixels.ConclusionsUsing these three OCT systems, we imaged the anterior segment of the human eye before and after accommodation, which showed similar results among the different systems. The system using the CMOS camera with an ultra-long scan depth, high resolution and high scan speed exhibited the best overall performance and therefore was recommended for imaging real-time accommodation.

Axial elongation measured by long scan depth optical coherence tomography during pilocarpine-induced accommodation in intraocular lens-implanted eyes

We used an ultra-long scan depth optical coherence tomography (UL-OCT) system to investigate changes in axial biometry of pseudophakic eyes during pilocarpine- induced accommodation. The right eyes from 25 healthy subjects (age range 49 to 84 years) with an intraocular lens (IOL) were imaged twice in the non-accommodative and the accommodative states. A custom-built UL-OCT instrument imaged the whole eye. Then accommodation was induced by two drops of 0.5% pilocarpine hydrochloride separated by a 5-minute interval. Following the same protocol, images were acquired again 30 minutes after the first drop. The central corneal thickness (CCT), anterior chamber depth (ACD), IOL thickness (IOLT), and vitreous length (VL) were obtained using custom automated software. The axial length (AL) was calculated by summing the CCT, ACD, IOLT, and VL. With accommodation, ACD increased by +0.08 ± 0.09 mm, while the VL decreased by −0.04 ± 0.09 mm (paired t-test each, P<0.05). CCT and IOLT remained constant during accommodation (P > 0.05). The non-accommodative AL was 23.47 ± 0.93 mm, and it increased by +0.04 ± 0.04 mm after accommodation (P<0.01). The AL increased and the IOL moved backward during pilocarpine-induced accommodation in pseudophakic eyes.

Characterization of Soft Contact Lens Fitting Using Ultra-Long Scan Depth Optical Coherence Tomography.

Objectives To evaluate the centration and movement of soft contact lenses and to verify the repeatability of two repeated measurements of the lens centration and movement using ultra-long scan depth optical coherence tomography (UL-OCT). Methods A 1-day Acuvue® Define™ lens was tested on both eyes of 10 subjects (5 males and 5 females; mean age, 31.6 years). The centration and blink-induced movement of the contact lens were measured using UL-OCT at 5 min and 30 min after insertion. The measurements were repeated once at each checkpoint. Results Good repeatability was found in the lens centration and movement between the two repeated measurements at either checkpoint. The values of the lens movement were 0.457 ± 0.248 mm and 0.402 ± 0.229 mm at 5 min and decreased to 0.197 ± 0.065 mm and 0.211 ± 0.110 mm at 30 min after insertion for the right and left eyes, respectively (P < 0.05). Conclusions The custom-built UL-OCT presented good repeatability of centration and movement in Define lenses at 5 min and 30 min after insertion. Most of the lenses were centered temporal and inferior to the cornea during the first 30 min wearing period. Compared with 5 min after insertion, the lens was centered better and exhibited less movement at 30 min.

In Vivo Observation of Lens Regeneration in Rat Using Ultra-Long Scan Depth Optical Coherence Tomography.

To evaluate morphologic changes of lens regeneration in rats in vivo after extracapsular lens extraction (ECLE) by ultra-long scan depth optical coherence tomography (UL-OCT). A total of 42 Sprague-Dawley rats were used in this study. We performed ECLE on the right eyes of animals in the surgery group (n = 34). Biomicroscopy and UL-OCT scans were carried out for the surgery group immediately (within 1 hour postoperatively) and at days 1 and 3, weeks 1 and 2, and months 1, 2, and 3 postoperatively. After in vivo examination, three animals of the surgery group were euthanized at each time point for histology study, while the other 10 animals were examined continuously at those time points. The regenerated lens was evaluated in OCT images at 2 and 3 months postoperatively. The control group consisted of eight untreated rats that had OCT examination at the age of 5 months. Lens regeneration could be observed from 2 weeks postoperatively. Regeneration was mainly at the peripheral capsular bag in the first month and central region thereafter. The average thickness of regenerated lenses was 2222 ± 309 and 2324 ± 352 μm at 2 and 3 months, respectively. Regeneration was faster in the first 2 months and slowed down thereafter. Although anterior capsule opening and posterior capsule adhesion and wrinkling existed, the regenerated lens still could form a relatively regular shape, however, the size was much smaller than that of the normal lenses from rats with the same age. Ultra-long OCT provides longitudinal data of the process of lens regeneration on a single individual rat in vivo, which may allow one to follow and compare the lens regenerative process under different interventions or therapy after ECLE in rats.

An Optical Section-Assisted In Vivo Rabbit Model for Capsular Bend and Posterior Capsule Opacification Investigation

PurposeTo establish an optical section-assisted in vivo rabbit model for capsular bend and posterior capsule opacification (PCO) investigation.MethodsA total of 10 rabbits underwent phacoemulsification surgery and intraocular lens (IOL) implantation. On the basis of the relationship between the anterior capsule and IOL, the rabbits were divided into complete overlap and incomplete overlap groups, in which six and four rabbits were included, respectively. The capsular bend optical sections were assessed using ultra-long scan depth optical coherence tomography (UL-OCT), and posterior capsule opacification was evaluated with slit lamp on postoperative day 3, 7, 14, and 28. In addition, histopathological section was used to verify the accuracy of capsular bend type captured by OCT in three rabbits.ResultsBased on the special animal model, six capsular bend types were observed, namely, anterior (A), middle (M), posterior (P), detachment (D), funnel (Fun) and furcate adhesion (Fur). On day 3, capsular bend began to form. On 14 days, the capsular bends were comprised of A, M and D types, which were almost maintained until day 28. Histopathological section findings were consistent with optical sectioning results. In the incomplete and complete groups, the earliest PCO within the optical zone were on day 7 and 28, respectively. The incomplete group exhibited higher incidence and faster PCO on day 7 (p = 0.038) and 14 (p = 0.002).ConclusionsThis animal model not only mimics capsular bend evolution and PCO processes but also produces OCT optical section images equivalent to and more repeatable than histopathology, thereby providing a promising method for the further investigations of PCO.

Biometry of anterior segment of human eye on both horizontal and vertical meridians during accommodation imaged with extended scan depth optical coherence tomography.

PurposeTo 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.MethodsTwenty pre-presbyopic volunteers, aged between 24 and 30, were recruited. The ocular anterior segment of each subject was imaged using an extended scan depth OCT under non- and 3.0 diopters (D) of accommodative demands on both horizontal and vertical meridians. All the images were analyzed to yield the following parameters: pupil diameter (PD), anterior chamber depth (ACD), anterior and posterior surface curvatures of the crystalline lens (ASC and PSC) and the lens thickness (LT). Two consecutive measurements were performed to assess the repeatability and reproducibility of this OCT. They were evaluated by calculating the within-subject standard deviation (SD), a paired t-test, intra-class correlation coefficients (ICC) and the coefficient of repeatability/reproducibility (CoR).ResultsThere were no significant differences between two consecutive measurements on either horizontal or vertical meridians under both two different accommodative statuses (P>0.05). The ICC for all parameters ranged from 0.775 to 0.998, except for the PSC (0.550) on the horizontal meridian under the non-accommodative status. In addition, the CoR for most of the parameters were excellent (0.004% to 4.89%). In all the parameters, only PD and PSC were found different between the horizontal and vertical meridians under both accommodative statuses (P<0.05). PD, ACD, ASC and PSC under accommodative status were significantly smaller than those under the non-accommodative status, except that the PSC at the vertical meridian did not change. In addition, LT was significantly increased when accommodation.ConclusionThe extended scan depth OCT successfully measured the dimensions of the anterior eye during accommodation with good repeatability and reproducibility on both horizontal and vertical meridians. The asymmetry of lens posterior surface and oval-shaped pupil were found during accommodation.

Corneal Reshaping and Wavefront Aberrations During Overnight Orthokeratology

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.

Whole Eye Axial Biometry During Accommodation Using Ultra-long Scan Depth Optical Coherence Tomography

To investigate changes of whole eye axial biometry during accommodation using ultra-long scan depth optical coherence tomography (UL-OCT). Prospective, observational case series. Twenty-one adult subjects were enrolled. Using UL-OCT, the left eye of each subject was imaged with relaxed diopters (0 D) and accommodative stimuli (+6 D). Full eye biometry included central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness, vitreous length, and axial length (AL). During accommodation (+6 D), the axial biometry of the whole eye changed significantly. Compared to the rest state, ACD at the accommodative state decreased significantly from 3.128 ± 0.305mm to 2.961 ± 0.298mm (paired t test, P < .001). The lens thickness increased significantly from 3.723 ± 0.237mm to 3.963 ± 0.234mm (P < .001). The vitreous length decreased significantly from 17.129 ± 0.864mm to 17.057 ± 0.848mm (P < .001). AL was 24.519 ± 0.917mm at the rest state and increased to 24.545 ± 0.915mm with+6 D accommodation stimulus. The elongated AL of 26.1 ± 13.4μm between the rest and accommodative states was significant (P < .001). During accommodation, whole eye axial biometry changed, including a decrease in ACD and vitreous length and an increase in lens thickness and AL. UL-OCT provides an alternative method thatis suitable for full eye biometry during accommodation.

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

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. 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. 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). 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.

Axial Biometry of the Entire Eye Using Ultra-Long Scan Depth Optical Coherence Tomography

To assess the repeatability of axial biometry of the entire eye using ultra-long scan depth optical coherence tomography (OCT) and to investigate the agreement with IOLMaster measurements (Carl Zeiss Meditec). Prospective, observational case series. There were 37 adult subjects enrolled in group 1 and 12 adult subjects enrolled in group 2. Using ultra-long scan depth OCT, the left eyes of these groups were measured in 2 separate sessions. The images were processed by a manual method and custom-developed automatic software. A model eye was imaged for verification. The subjects in group 2 were imaged using ultra-long scan depth OCT and using the IOLMaster for axial length measurement comparison. All measured parameters of the model eye matched the geometric parameters. In group 1, there were no significant differences in all measured parameters using automatic and manual segmentation methods (P > .05, paired t test). The percentage of coefficient of repeatability of segments ranged from 0.3% to 3.9%. The corresponding interclass correlation coefficients ranged from 0.946 to 0.999. The correlation between the results using automatic and manual segmentation methods appeared to be strong (R(2)= 0.999; P < .05). In group 2, the axial length of the eye measured by the IOLMaster matched the results obtained by ultra-long scan depth OCT with the automatic method (R1(2)= 0.987; P < .05) and the manual method (R2(2)= 0.988; P < .05). Automatic axial biometry using ultra-long scan depth OCT successfully measured each segment of the entire eye with good repeatability. With further development of automatic segmentation, ultra-long scan depth OCT seems to be a promising tool in the axial biometry of the entire eye.

The Role of Axial Resolution of Optical Coherence Tomography on the Measurement of Corneal and Epithelial Thicknesses

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. 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. 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. 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.

Ultra-high resolution and long scan depth optical coherence tomography with full-phase detection for imaging the ocular surface

We used a unique combination of four state-of-the-art technologies to achieve a high performance spectral domain optical coherence tomography system suitable for imaging the entire ocular surface. An ultra-high resolution, extended depth range, full-phase interferometry, and high-speed complementary metal-oxide semiconductor transistor camera detection provided unprecedented performance for the precise quantification of a wide range of the ocular surface. We demonstrated the feasibility of this approach by obtaining high-speed and high-resolution images of a model eye beyond the corneal–scleral junction. Surfaces determined from the images with a segmentation algorithm demonstrated excellent accuracy and precision.

Anterior Segment Biometry during Accommodation Imaged with Ultralong Scan Depth Optical Coherence Tomography

To measure by ultralong scan depth optical coherence tomography (UL-OCT) dimensional changes in the anterior segment of human eyes during accommodation. Evaluation of diagnostic test or technology. Forty-one right eyes of healthy subjects with a mean age of 34 years (range, 22-41 years) and a mean refraction of -2.5 ± 2.6 diopters were imaged in 2 repeated measurements at minimal and maximal accommodations. A specially adapted and designed UL-OCT instrument was used to image from the front surface of the cornea to the back surface of the crystalline lens. Custom software corrected the optical distortion of the images and yielded the biometric measurements. The coefficient of repeatability and the intraclass correlation coefficient were calculated to evaluate the repeatability and reliability. Anterior segment parameters and associated repeatability and reliability upon accommodation. The dimensional results included central corneal thickness (CCT), anterior chamber depth and width (ACD, ACW), pupil diameter (PD), lens thickness (LT), anterior segment length (ASL = ACD + LT), lens central position (LCP = ACD + 1/2LT), and horizontal radii of the lens anterior and posterior surface curvatures (LAC, LPC). Repeated measurements of each variable within each accommodative state did not differ significantly (P>0.05). The coefficients of repeatability (CORs) and intraclass correlation coefficients for CCT, ACW, ACD, LT, LCP, and ASL were excellent (1.2%- 3.59% and 0.998-0.877, respectively). They were higher for PD (18.90%-21.63% and 0.880-0.874, respectively) and moderate for LAC and LPC (34.86%-42.72% and 0.669-0.251, respectively) in the 2 accommodative states. Compared with minimal accommodation, PD, ACD, LAC, LPC, and LCP decreased and LT and ASL increased significantly at maximal accommodation (P<0.05), whereas CCT and ACW did not change (P>0.05). The UL-OCT measured changes in anterior segment dimensions during accommodation with good repeatability and reliability. During accommodation, the back surface of the lens became steeper as the lens moved forward. The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Automatic Segmentation of the Central Epithelium Imaged With Three Optical Coherence Tomography Devices

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. 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-μm axial resolution, ultralong scan depth OCT (UL-OCT) with a 7.5-μm resolution, and commercial RTVue OCT with a 5-μm 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. 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 μm, 526.1 ± 23.4 μm, and 525.2 ± 23.7 μm for UHR-OCT, UL-OCT, and RTVue, respectively. The average ET was 53.2 ± 2.0 μm, 54.1 ± 3.0 μm, and 52.1 ± 2.5 μm 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). 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.

Repeated Measurements of the Anterior Segment During Accommodation Using Long Scan Depth Optical Coherence Tomography

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.

Characterization of Soft Contact Lens Edge Fitting Using Ultra-High Resolution and Ultra-Long Scan Depth Optical Coherence Tomography

To characterize the edge fitting of soft contact lenses using ultra-high resolution optical coherence tomography (UHR-OCT) and ultra-long scan depth optical coherence tomography (UL-OCT). A total of 20 participants (11 men, 9 women; mean age, 32.3 years) were recruited. Four different types of soft contact lenses were randomly fitted to both eyes of each subject on two separate visits. After 30 minutes, the horizontal meridians of the corneal center, midperiphery, and limbus were imaged by UHR-OCT. UL-OCT imaged each lens in vitro and the ocular surface of a physical model eye. Angle-edged lenses had significantly less conjunctival buildup than did round-edged lenses (P = 0.008). Limbal post-lens tear film gaps were present in 42% of the eyes, with the round-edged lenses having the most at 68%. Similarly, post-lens tear film gaps at the corneal mid-periphery were present in 47% of all eyes, with the round-edged lens having the most at 75%. Mismatches between the lens and the ocular surface were simulated based on UL-OCT images of the in vitro lenses and the model eye. The existence of tear film gaps and touching points were predicted in the simulation. The soft contact lens edge fitting was characterized by the conjunctival buildup and tear film gaps. Different types of contact lenses presented different levels of conjunctival buildup as well as different frequencies of tear film gaps. The findings by UHR-OCT were predicted in the simulation by UL-OCT. The application of these new technologies may open new ways of designing lenses and evaluating their fit.

Extended scan depth optical coherence tomography for evaluating ocular surface shape

Spectral domain optical coherence tomography (SD-OCT) with extended scan depth makes it possible for quantitative measurement of the entire ocular surface shape. We proposed a novel method for ocular surface shape measurement using a custom-built anterior segment SD-OCT, which will serve on the contact lens fitting. A crosshair alignment system was applied to reduce the misalignment and tilting of the eye. An algorithm was developed to automatically segment the ocular surface. We also described the correction of the image distortion from the segmented dataset induced by the nontelecentric scanning system and tested the accuracy and repeatability. The results showed high accuracy of SD-OCT in measuring a bicurved test surface with a maximum height error of 17.4 μm. The repeatability of in vivo measurement was also good. The standard deviations of the height measurement within a 14-mm wide range were all less than 35 μm. This work demonstrates the feasibility of using extended depth SD-OCT to perform noninvasive evaluation of the ocular surface shape.