Semiautomatic extraction algorithm for images of the ciliary muscle

Impact of accommodative insufficiency and accommodative/vergence therapy on ciliary muscle thickness in the eye

PURPOSE

Recent evidence suggests that the ciliary muscle apical fibres are most responsive to accommodative load; however, the structure of the ciliary muscle in individuals with accommodative insufficiency is unknown. This study examined ciliary muscle structure in individuals with accommodative insufficiency (AI). We also determined the response of the ciliary muscle to accommodative/vergence therapy and increasing accommodative demands to investigate the muscle's responsiveness to workload.

METHODS

Subjects with AI were enrolled and matched by age and refractive error with subjects enrolled in another ciliary muscle study as controls. Anterior segment optical coherence tomography was used to measure the ciliary muscle thickness (CMT) at rest (0D), maximum thickness (CMTMAX) and over the area from 0.75 mm (CMT0.75) to 3 mm (CMT3) posterior to the scleral spur of the right eye. For those with AI, the ciliary muscle was also measured at increasing levels of accommodative demand (2D, 4D and 6D), both before and after accommodative/vergence therapy.

RESULTS

Sixteen subjects with AI (mean age = 17.4 years, SD = 8.0) were matched with 48 controls (mean age = 17.8 years, SD = 8.2). On average, the controls had 52-72 μm thicker ciliary muscles in the apical region at 0D than those with AI (p = 0.03 for both CMTMAX and CMT 0.75). Differences in thickness between the groups in other regions of the muscle were not statistically significant. After 8 weeks of accommodative/vergence therapy, the CMT increased by an average of 22-42 μm (p ≤ 0.04 for all), while AA increased by 7D (p < 0.001).

CONCLUSIONS

This study demonstrated significantly thinner apical ciliary muscle thickness in those with AI and that the ciliary muscle can thicken in response to increased workload. This may explain the mechanism for improvement in signs and symptoms with accommodative/vergence therapy.

Performance of the Deep Neural Network Ciloctunet, Integrated with Open-Source Software for Ciliary Muscle Segmentation in Anterior Segment OCT Images, Is on Par with Experienced Examiners

Anterior segment optical coherence tomography (AS-OCT), being non-invasive and well-tolerated, is the method of choice for an in vivo investigation of ciliary muscle morphology and function. The analysis requires the segmentation of the ciliary muscle, which is, when performed manually, both time-consuming and prone to examiner bias. Here, we present a convolutional neural network trained for the automatic segmentation of the ciliary muscle in AS-OCT images. Ciloctunet is based on the Freiburg U-net and was trained and validated using 1244 manually segmented OCT images from two previous studies. An accuracy of 97.5% for the validation dataset was achieved. Ciloctunet's performance was evaluated by replicating the findings of a third study with 180 images as the test data. The replication demonstrated that Ciloctunet performed on par with two experienced examiners. The intersection-over-union index (0.84) of the ciliary muscle thickness profiles between Ciloctunet and an experienced examiner was the same as between the two examiners. The mean absolute error between the ciliary muscle thickness profiles of Ciloctunet and the two examiners (35.16 µm and 45.86 µm) was comparable to the one between the examiners (34.99 µm). A statistically significant effect of the segmentation type on the derived biometric parameters was found for the ciliary muscle area but not for the selective thickness reading ("perpendicular axis"). Both the inter-rater and the intra-rater reliability of Ciloctunet were good to excellent. Ciloctunet avoids time-consuming manual segmentation, thus enabling the analysis of large numbers of images of ample study cohorts while avoiding possible examiner biases. Ciloctunet is available as open-source.

Automated segmentation of the ciliary muscle in OCT images using fully convolutional networks

Quantifying shape changes in the ciliary muscle during accommodation is essential in understanding the potential role of the ciliary muscle in presbyopia. The ciliary muscle can be imaged in-vivo using OCT but quantifying the ciliary muscle shape from these images has been challenging both due to the low contrast of the images at the apex of the ciliary muscle and the tedious work of segmenting the ciliary muscle shape. We present an automatic-segmentation tool for OCT images of the ciliary muscle using fully convolutional networks. A study using a dataset of 1,039 images shows that the trained fully convolutional network can successfully segment ciliary muscle images and quantify ciliary muscle thickness changes during accommodation. The study also shows that EfficientNet outperforms other current backbones of the literature.

Diagnostic imaging of the ciliary body: Technologies, outcomes, and future perspectives

The ciliary body (CB) is part of the uvea and is a complex, highly specialized structure with multiple functions and significant relationships with nearby structures. Its functions include the aqueous humor (AH) production in the ciliary processes, the regulation of the AH output through the uveoscleral pathway, and accommodation, which depends on the ciliary muscle. Also, the CB is an important determinant of angle width as it forms part of the ciliary sulcus. Until recently, knowledge of the CB was based on histological studies. However, this structure can currently be assessed in vivo using imaging techniques such as ultrasound biomicroscopy (UBM) and optical coherence tomography (OCT). Both techniques have shown good reproducibility of their measurements allowing for quantification of CB dimensions and their localization. In effect, studies have shown a larger CB in myopia and its diminishing size with age. Swept-source OCT devices offer fast, non-invasive high-resolution imaging allowing the identification of multiple structures. UBM requires contact and is uncomfortable for the patient. However, this technique offers deeper imaging and therefore remains the gold standard for assessing the posterior chamber, ciliary processes, or zonula. The clinical utility of CB imaging includes its assessment in different types of glaucoma such as angle-closure, malignant or plateau iris. Diagnostic CB imaging is also invaluable for the assessment of ciliochoroidal detachment when suspected, the position after the implantation of a pre-crystalline or sulcus-sutured lenses, diagnosis or monitoring of cysts or tumors, sclerotomies after retinal surgery, intermediate uveitis, or accommodation.

Accommodative Exercises to Lower Intraocular Pressure

Purpose

This study investigated how a conscious change in ocular accommodation affects intraocular pressure (IOP) and ocular biometrics in healthy adult volunteers of different ages.

Methods

Thirty-five healthy volunteers without ocular disease or past ocular surgery, and with refractive error between −3.50 and +2.50 diopters, were stratified into 20, 40, and 60 year old (y.o.) age groups. Baseline measurements of central cornea thickness, anterior chamber depth, anterior chamber angle, cornea diameter, pupil size, and ciliary muscle thickness were made by autorefraction and optical coherence tomography (OCT), while IOP was measured by pneumotonometry. Each subject's right eye focused on a target 40 cm away. Three different tests were performed in random order: (1) 10 minutes of nonaccommodation (gazing at the target through lenses that allowed clear vision without accommodating), (2) 10 minutes of accommodation (addition of a minus 3 diopter lens), and (3) 10 minutes of alternating between accommodation and nonaccommodation (1-minute intervals). IOP was measured immediately after each test. A 20-minute rest period was provided between tests. Data from 31 subjects were included in the study. ANOVA and paired t-tests were used for statistical analyses.

Results

Following alternating accommodation, IOP decreased by 0.7 mmHg in the right eye when all age groups were combined (p = 0.029). Accommodation or nonaccommodation alone did not decrease IOP. Compared to the 20 y.o. group, the 60 y.o. group had a thicker ciliary muscle within 75 μm of the scleral spur, a thinner ciliary muscle at 125–300 μm from the scleral spur, narrower anterior chamber angles, shallower anterior chambers, and smaller pupils during accommodation and nonaccommodation (p's < 0.01).

Conclusion

Alternating accommodation, but not constant accommodation, significantly decreased IOP. This effect was not lost with aging despite physical changes to the aging eye. A greater accommodative workload and/or longer test period may improve the effect.

In-vivo anterior segment OCT imaging provides unique insight into cerulean blue-dot opacities and cataracts in Down syndrome

Down syndrome (DS) is frequently associated with cataract, but there remains scant information about DS cataract morphology. Supra-nuclear cataracts in DS have been proposed as indicative of beta-amyloid (Aβ) aggregation and thus potential biomarkers for Alzheimer’s (AD). This study employed anterior segment OCT (AS-OCT) and slit-lamp (SL) photography to image the crystalline lens in DS, compared with adult controls. Lens images were obtained post-dilation. Using MATLAB, AS-OCT images were analysed and lens opacities calculated as pixel intensity and area ratios. SL images were classified using LOCS III. Subjects were n = 28 DS (mean ± SD 24.1 ± 14.3years), and n = 36 controls (54.0 ± 3.4years). For the DS group, AS-OCT imaging revealed the frequent presence of small dot opacities (27 eyes, 50%) in the cortex and nucleus of the lens, covering an area ranging from 0.2–14%. There was no relation with age or visual acuity and these dot opacities (p > 0.5) and they were not present in any control lenses. However, their location and morphology does not coincide with previous reports linking these opacities with Aβ accumulation and AD. Four participants (14%) in the DS group had clinically significant age-related cataracts, but there was no evidence of early onset of age-related cataracts in DS.

Review of the application of the open-source software CilOCT for semi-automatic segmentation and analysis of the ciliary muscle in OCT images

Presbyopia and myopia research shows a growing interest in ciliary muscle biometry using optical coherence tomography (OCT). Until now, segmentation of the ciliary muscle is often performed manually using either custom-developed programs or image processing software. Here we present a novel software for semi-automatic segmentation of the ciliary muscle. It provides direct import of OCT images in DICOM format, a standardized procedure for segmentation, image distortion correction, the export of anatomical ciliary muscle landmarks, like ciliary muscle apex and scleral spur, as well as a continuous thickness profile of the ciliary muscle as a novel way of analysis. All processing steps are stored as XML files, fostering documentation and reproducibility of research through the possibility of replicating the analysis. Additionally, CilOCT supports batch processing for the automated analysis of large numbers of images and the respective data export to tabulated text files based on the stored XML files. CilOCT was successfully applied in several studies and their results will be summarized in this paper.

Ciliary muscle dimensions by swept-source optical coherence tomography and correlation study in a large population

PURPOSE

To examine ciliary muscle (CM) dimensions in vivo by swept-source optical coherence tomography (SS-OCT) in a large healthy population. To assess the reproducibility of CM measurements and correlations with different parameters.

METHODS

In this cross-sectional study, the following CM measurements were made in 495 eyes of 495 subjects in the temporal and nasal quadrants: length (CML), area (CMA) and thickness at distances of 1000 μm (CMT1), 2000 μm (CMT2) and 3000 μm (CMT3) from the scleral spur using the SS-OCT DRI-Triton^® (Topcon, Tokyo, Japan). These dimensions were then assessed for correlations with the factors age, gender, refractive error, anterior chamber angle (ACA) and intraocular pressure (IOP). The reproducibility of CM measurements was determined in 85 of the participants.

RESULTS

Mean age was 41.4 ± 17.5 years (range 5-83). The following means were recorded as follows: CML = 4.57 ± 0.73 mm (range 2.16-6.97), CMA = 1.35 ± 0.31 mm² (2.04-5.45), CMT1 = 558 ± 98 μm (299-891), CMT2 = 366 ± 100 μm (89-629) and CMT3 = 210 ± 75 μm (36-655). Negative correlation was detected between CML/CMA and age (R = -0.516/R = -0.404; p < 0.001) and refractive error (R = -0.519/R = -0.538; p < 0.001). No gender differences were observed (p ≥ 0.150). Both CML and CMA were correlated with ACA (R = 0.498 and 0.546; p < 0.001) and slightly with IOP (R = -0.175; p < 0.001). The reproducibility of the CM measurements was excellent (intraclass correlation coefficient ≥0.878).

CONCLUSIONS

Swept-source optical coherence tomography is a valid tool for in vivo CM measurements. Our data indicate a larger CM in myopes and its diminishing size with age.

Effect of age in the ciliary muscle during accommodation: Sectorial analysis

PURPOSE

To compare changes in the ciliary muscle area at different sectors between pre-presbyopic and presbyopic eyes during accommodation by means of an anterior segment optical coherence tomographer (OCT).

METHODS

The anterior ciliary muscle area was measured in 20 healthy and phakic pre-presbyopic eyes, whose mean age was 23.3±4.4 years, and in 20 healthy and phakic presbyopic eyes, whose mean age was 46.5±5.2 years. The relative change in the cross-sectional area of the ciliary muscle was measured at the nasal, inferior, and temporal sectors between 0 and -3 D of vergence, in -1 D step. A linear model was used to assess the correlation of each eye parameter with the accommodative demand.

RESULTS

Each population group showed a significant increase in the anterior ciliary muscle area for each sector. The maximum increase in the ciliary muscle area within the pre-presbyopic group was about 30%, and for the presbyopic one was about 25%. At the same time, it was obtained that the larger the vergence, the larger the variability. Furthermore, the linear model showed a positive tendency between the change in the ciliary muscle area of each sector and the vergence for both population groups, which coefficient of determination was in all cases greater than 0.93.

CONCLUSION

The anterior ciliary muscle area tends to increase with accommodation. The presbyopic nasal, inferior, and temporal ciliary muscle seem to have the same contractile capability as the young presbyopic ciliary muscle. These results might help to increase the evidences in the knowledge regarding the modern understanding of accommodation biometry and biomechanics.

Ciliary muscle thickness profiles derived from optical coherence tomography images

The purpose of this study was to provide an in-depth analysis of the ciliary muscle's (CM) morphological changes during accommodation by evaluating CM thickness (CMT) profiles. The CM of 15 near-emmetropic subjects (age 20-39) was imaged via optical coherence tomography (OCT) during far (0 D) and near vision (3 D). A custom-made Java-based program was used for semi-automatic CM segmentation and thickness measurements. CMT profiles were generated to determine regions of the largest shape changes. The results revealed on average a thinning within the first 0.25 mm and a thickening from 0.36 to 1.48 mm posterior to scleral spur when accommodating from 0 to 3 D. In contrast to previous analyses, this method offers pixel-wise reconstruction of CM shapes and quantification of accommodative change across the entire muscle boundary.

Biomechanical Evaluations of Ocular Injury Risk for Blast Loading

Ocular trauma is one of the most common types of combat injuries resulting from the exposure of military personnel with improvised explosive devices. The injury mechanism associated with the primary blast wave is poorly understood. We employed a three-dimensional computational model, which included the main internal ocular structures of the eye, spatially varying thickness of the cornea-scleral shell, and nonlinear tissue properties, to calculate the intraocular pressure and stress state of the eye wall and internal ocular structure caused by the blast. The intraocular pressure and stress magnitudes were applied to estimate the injury risk using existing models for blunt impact and blast loading. The simulation results demonstrated that blast loading can induce significant stresses in the different components of the eyes that correlate with observed primary blast injuries in animal studies. Different injury models produced widely different injury risk predictions, which highlights the need for experimental studies evaluating mechanical and functional damage to the ocular structures caused by the blast loading.

Variability of manual ciliary muscle segmentation in optical coherence tomography images

Optical coherence tomography (OCT) offers new options for imaging the ciliary muscle allowing direct in vivo visualization. However, variation in image quality along the length of the muscle prevents accurate delineation and quantification of the muscle. Quantitative analyses of the muscle are accompanied by variability in segmentation between examiners and between sessions for the same examiner. In processes such as accommodation where changes in muscle thickness may be tens of microns- the equivalent of a small number of image pixels, differences in segmentation can influence the magnitude and potentially the direction of thickness change. A detailed analysis of variability in ciliary muscle thickness measurements was performed to serve as a benchmark for the extent of this variability in studies on the ciliary muscle. Variation between sessions and examiners were found to be insignificant but the magnitude of variation should be considered when interpreting ciliary muscle results.

Semiautomatic procedure to assess changes in the eye accommodative system

PURPOSE

The aim of this pilot study was to evaluate a new semiautomatic procedure to assess in vivo changes in the crystalline lens and ciliary muscle during accommodation.

METHODS

A total of 14 subjects were divided into two groups, young (aged between 20 and 25 years) and adult (aged between 35 and 40 years), and measured with an anterior segment optical coherence tomography. A semiautomatic procedure was implemented to measure the central lens thickness (CLT), anterior lens radius (ALR) and the ciliary muscle area (CMA) for the unaccommodated eye and for a vergence of - 3.00 D.

RESULTS

The CLT increase for each population group was smaller than 5%, and the dispersion of each group was similar between them. Contrariwise, the reduction in the ALR was about 30% for both groups, although the young one showed the largest variability. The CMA increase was smaller than 30% for both groups, and the dispersion was similar between them. For each metric, differences between both groups were not statistically significant.

CONCLUSIONS

The semiautomatic procedure seems to be useful for the in vivo analysis of the accommodative system. Additionally, the results obtained showed that changes in the CLT were much smaller compared to those obtained for the ALR or CMA.

Accuracy and Repeatability of an Anterior Segment Swept-Source Optical Coherence Tomographer

OBJECTIVES

To assess accuracy and repeatability of the CASIA swept-source optical coherence tomographer (SS-OCT) in measuring contact lens (CL) radii of curvature and thicknesses compared with verified CL parameters and to investigate intrasession and intersession repeatability of the CASIA SS-OCT in measuring epithelial and total corneal thicknesses.

METHODS

Rigid CLs with varying radii of curvature (front, rf; back, rb) and thicknesses were imaged with the CASIA SS-OCT across two sessions. Contact lens parameters were measured from processed images using an automated MATLAB program and were compared with parameters verified using standard techniques. Central epithelial and total corneal thicknesses of 43 normal subjects were measured to assess intrasession and intersession repeatability of the CASIA SS-OCT.

RESULTS

No significant differences (P>0.05) were found in rigid CL rf and central and peripheral thickness measurements compared with verified CL parameters. However, the rb values obtained from the CASIA SS-OCT were consistently 0.2 mm flatter than the verified rb values (P<0.001) along horizontal and vertical meridians. Bland-Altman analysis revealed excellent intrasession agreement with mean differences of 0.004 and 0.003 mm for rf and rb, 0.000 mm for CL thickness and 0.372 and 0.395 μm for epithelial and total corneal thicknesses, respectively. Similarly, mean intersession differences of 0.020 and 0.000 mm for rf and CL thickness and 0.100 and 0.984 μm for epithelial and total corneal thicknesses were found, respectively. Ninety-five percentage confidence intervals across one or two sessions indicated insignificant undermeasurement or overmeasurement for CL rf, and corneal thicknesses, but significant bias toward overmeasurement for CL rb was found across two sessions.

CONCLUSIONS

The CASIA SS-OCT produces accurate measurements of CL parameters compared with verified values. Inbuilt distortion correction in this instrument necessitated no further correction of scanned images and provided high intrasession and intersession repeatability in measuring both CLs and corneal thicknesses. Further investigation of discrepancies in rb measurements is warranted.

The Effect of Age, Accommodation, and Refractive Error on the Adult Human Eye

PURPOSE

To quantify changes in ocular dimensions associated with age, refractive error, and accommodative response, in vivo, in 30- to 50-year-old human subjects.

METHODS

The right eyes of 91 adults were examined using ultrasonography, phakometry, keratometry, pachymetry, interferometry, anterior segment optical coherence tomography, and high-resolution magnetic resonance imaging. Accommodation was measured subjectively with a push-up test and objectively using open-field autorefraction. Regression analyses were used to assess differences in ocular parameters with age, refractive error, and accommodation.

RESULTS

With age, crystalline lens thickness increased (0.03 mm/yr), anterior lens curvature steepened (0.11 mm/yr), anterior chamber depth decreased (0.02 mm/yr), and lens equivalent refractive index decreased (0.001/yr) (all p < 0.01). With increasing myopia, there were significant increases in axial length (0.37 mm/D), vitreous chamber depth (0.34 mm/D), vitreous chamber height (0.09 mm/D), and ciliary muscle ring diameter (0.10 mm/D) (all p < 0.05). Increasing myopia was also associated with steepening of both the cornea (0.16 mm/D) and anterior lens surface (0.011 mm/D) (both p < 0.04). With accommodation, the ciliary muscle ring diameter decreased (0.08 mm/D) and the muscle thinned posteriorly (0.008 mm/D), allowing the lens to shorten equatorially (0.07 mm/D) and thicken axially (0.06 mm/D) (all p < 0.03).

CONCLUSIONS

Refractive error is significantly correlated with not only the axial dimensions but also the anterior equatorial dimension of the adult eye. Further testing and development of accommodating intraocular lenses should account for differences in patients' preoperative refractive error.

Quantification of the ciliary muscle and crystalline lens interaction during accommodation with synchronous OCT imaging

Two SD-OCT systems and a dual channel accommodation target were combined and precisely synchronized to simultaneously image the anterior segment and the ciliary muscle during dynamic accommodation. The imaging system simultaneously generates two synchronized OCT image sequences of the anterior segment and ciliary muscle with an imaging speed of 13 frames per second. The system was used to acquire OCT image sequences of a non-presbyopic and a pre-presbyopic subject accommodating in response to step changes in vergence. The image sequences were processed to extract dynamic morphological data from the crystalline lens and the ciliary muscle. The synchronization between the OCT systems allowed the precise correlation of anatomical changes occurring in the crystalline lens and ciliary muscle at identical time points during accommodation. To describe the dynamic interaction between the crystalline lens and ciliary muscle, we introduce accommodation state diagrams that display the relation between anatomical changes occurring in the accommodating crystalline lens and ciliary muscle.

Distortion Correction of Visante Optical Coherence Tomography Cornea Images

PURPOSE

Quantitative biometry measurements from uncorrected anterior segment optical coherence tomography (AS-OCT) images are inaccurate because of spatial and optical distortions. Prior reported distortion correction equations for the Visante AS-OCT were not reproducible. The goal was to calculate the distortions and provide equations to correct corneal parameters for the Visante AS-OCT to get a central corneal radius of curvature from young and older subjects.

METHODS

Five contact lenses (CLs) of known front and back radii of curvature and central thickness were imaged using the Visante AS-OCT (Carl Zeiss, Dublin, CA). Contact lens surface coordinates from Visante images were identified and fitted with a circle using custom Matlab image analysis software. Spatial and optical distortions of the Visante image of the CL radii of curvature and thickness were calculated and corrected. Visante images were also captured from 24 younger (aged 21 to 36 years) and 30 older (aged 36 to 48 years) human subjects. Corneal radii of curvature and thickness measurements from these subjects were corrected, and intrasession and intersession repeatabilities of the corneal parameters were calculated.

RESULTS

Root mean square error of radius and power of the CL surfaces after distortion correction were 0.02 mm and 0.18D for the front and 0.011 mm and 0.11D for the back, respectively. Intraclass correlation coefficient for intrasession and intersession repeatability for all the corneal parameters from the human subjects was greater than 0.88 in both age groups.

CONCLUSIONS

A distortion correction algorithm was developed for the Visante AS-OCT and applied to extract human corneal radius of curvature measurements.

Diurnal variation of anterior scleral and conjunctival thickness

PURPOSE

To examine whether anterior scleral and conjunctival thickness undergoes significant diurnal variation over a 24-h period.

METHODS

Nineteen healthy young adults (mean age 22 ± 2 years) with minimal refractive error (mean spherical equivalent refraction -0.08 ± 0.39 D), had measures of anterior scleral and conjunctival thickness collected using anterior segment optical coherence tomography (AS-OCT) at seven measurement sessions over a 24-h period. The thickness of the temporal anterior sclera and conjunctiva were determined at six locations (each separated by 0.5 mm) at varying distances from the scleral spur (SS) for each subject at each measurement session.

RESULTS

Both the anterior sclera and conjunctiva were found to undergo significant diurnal variations in thickness over a 24-h period (both p < 0.01). The sclera and conjunctiva exhibited a similar pattern of diurnal change, with a small magnitude thinning observed close to midday, and a larger magnitude thickening observed in the early morning immediately after waking. The amplitude of diurnal thickness change was larger in the conjunctiva (mean amplitude 69 ± 29 μm) compared to the sclera (21 ± 8 μm). The conjunctiva exhibited its smallest magnitude of change at the SS location (mean amplitude 56 ± 17 μm) whereas the sclera exhibited its largest magnitude of change at this location (52 ± 21 μm).

CONCLUSIONS

This study provides the first evidence of diurnal variations occurring in the thickness of the anterior sclera and conjunctiva. Studies requiring precise measures of these anatomical layers should therefore take time of day into consideration. The majority of the observed changes occurred in the early morning immediately after waking and were of larger magnitude in the conjunctiva compared to the sclera. Thickness changes at other times of the day were of smaller magnitude and generally not statistically significant.

Guinea pig ciliary muscle development

PURPOSE

The purpose of this study was to develop a method for quantifying guinea pig ciliary muscle volume (CMV) and to determine its relationship to age and ocular biometric measurements.

METHODS

Six albino guinea pigs' eyes were collected at each of five ages (n = 30 eyes). Retinoscopy and photography were used to document refractive error, eye size, and eye shape. Serial sections through the excised eyes were made and then labeled with an α-smooth muscle actin antibody. The ciliary muscle was then visualized with an Olympus BX51 microscope, reconstructed with Stereo Investigator (MBF Bioscience), and analyzed using Neurolucida Explorer (MBF Bioscience). Full (using all sections) and partial (using a subset of sections) reconstruction methods were used to determine CMV.

RESULTS

There was no significant difference between the full and partial volume determination methods (p = 0.86). The mean (±SD) CMV of the 1-, 10-, 20-, 30-, and 90-day-old eyes was 0.40 (±0.16) mm, 0.48 (±0.13) mm, 0.67 (±0.15) mm, 0.86 (±0.35) mm, and 1.09 (±0.63) mm, respectively. Ciliary muscle volume was significantly correlated with log age (p = 0.001), ocular length (p = 0.003), limbal circumference (p = 0.01), and equatorial diameter (p = 0.003). It was not correlated with refractive error (p = 0.73) or eye shape (p = 0.60). Multivariate regression determined that biometric variables were not significantly associated with CMV after adjustment for age.

CONCLUSIONS

Three-dimensional reconstruction was an effective means of determining CMV. These data provide evidence that ciliary muscle growth occurs with age in tandem with eye size in normal albino guinea pigs. Additional work is needed to determine the relationship between CMV and abnormal ocular growth.

Ciliary muscle thickness in anisometropia

PURPOSE

The purpose of this study was to investigate the relationships between ciliary muscle thickness (CMT), refractive error, and axial length both across subjects and between the more and less myopic eyes of adults with anisometropia.

METHODS

Both eyes of 29 adult subjects with at least 1.00 D of anisometropia were measured. Ciliary muscle thickness was measured at the maximum thickness (CMTMAX) and at 1.0 (CMT1), 2.0 (CMT2), and 3.0 mm (CMT3) posterior to the scleral spur, and also at the apical region (Apical CMTMAX = CMTMAX - CMT2, and Apical CMT1 = CMT1 - CMT2). Multilevel regression models were used to determine the relationship between the various CMT measures and cycloplegic refractive error or axial length, and to assess whether there are CMT differences between the more and less myopic eyes of an anisometropic adult.

RESULTS

CMTMAX, CMT1, CMT2, and CMT3 were negatively associated with mean refractive error (all p ≤ 0.03), and the strongest association was in the posterior region (CMT2 and CMT3). Apical CMTMAX and Apical CMT1, however, were positively associated with mean refractive error (both p < 0.0001) across subjects. Within a subject, i.e., comparing the two anisometropic eyes, there was no statistically significant difference in CMT in any region.

CONCLUSIONS

Similar to previous studies, across anisometropic subjects, a thicker posterior region of the ciliary muscle (CMT2 and CMT3) was associated with increased myopic refractive error. Conversely, shorter, more hyperopic eyes tended to have thicker anterior, apical fiber portions of their ciliary muscle (Apical CMTMAX and Apical CMT1). There was no difference between the two eyes for any CMT measurement, indicating that in anisometropia, an eye can grow longer and more myopic than its fellow eye without resulting in an increase in CMT.

Region-specific relationships between refractive error and ciliary muscle thickness in children

PURPOSE

To determine if there is a relationship between refractive error and ciliary muscle thickness in different muscle regions.

METHODS

An anterior segment optical coherence tomographer was used to measure cycloplegic ciliary muscle thicknesses at 1 mm (CMT1), 2 mm (CMT2), and 3 mm (CMT3) posterior to the scleral spur; maximum (CMTMAX) thickness was also assessed. An autorefractor was used to determine cycloplegic spherical equivalent refractive error (SPHEQ). Apical ciliary muscle fibers were obtained by subtracting corresponding CMT2 values from CMT1 and CMTMAX. Multilevel regression models were used to determine the relationship between ciliary muscle thickness in various regions of the muscle and refractive error.

RESULTS

Subjects included 269 children with a mean age of 8.71 ± 1.51 years and a mean refractive error of +0.41 ± 1.29 diopters. In linear models with ciliary muscle thicknesses and SPHEQ, SPHEQ was significantly associated only with CMT2 (β = -11.34, P = 0.0008) and CMT 3 (β = -6.97, P = 0.007). When corresponding values of CMT2 were subtracted from CMT1 and CMTMAX, apical fibers at CMT1 (β = 14.75, P < 0.0001) and CMTMAX (β = 18.16, P < 0.0001) had a significant relationship with SPHEQ.

CONCLUSIONS

These data indicated that in children the posterior ciliary muscle fibers are thicker in myopia (CMT2 and CMT3), but paradoxically, the apical ciliary muscle fibers are thicker in hyperopia (CMTMAX and CMT1). This may be the first evidence that hyperopia is associated with a thicker apical ciliary muscle region.

The effect of phenylephrine on the ciliary muscle and accommodation

PURPOSE

To objectively measure changes in the human ciliary muscle dimensions in vivo after instillation of topical phenylephrine, a mydriatic and vasodilating agent.

METHODS

A cross-sectional study of 25 healthy young adults was conducted. Measurements of pupil size, accommodation, and ciliary muscle thickness were made both before and 30 min after instillation of 1% proparacaine and 2.5% phenylephrine. Accommodation was measured in three ways: subjectively using a push-up technique and Royal Air Force (RAF) rule, and objectively using both the Grand Seiko autorefractor and PowerRefractor. Images of the temporal ciliary muscle were acquired using the Visante Anterior Segment Optical Coherence Tomographer (OCT). Ciliary muscle images were objectively analyzed using a computer-based segmentation technique.

RESULTS

Amplitude of accommodation using the push-up test was reduced by about 1 D with phenylephrine (p < 0.001). Phenylephrine did not change the accommodative response to a 4 D Badal target as measured by either autorefraction or photorefraction (p > 0.30). There was statistically significant thickening of the anterior region and thinning of the posterior region of the ciliary muscle with accommodation (p < 0.001, all locations). Phenylephrine did not affect either baseline ciliary muscle thickness or the accommodative contraction of the muscle (p > 0.09).

CONCLUSIONS

Low-dose phenylephrine does not affect ciliary muscle dimensions, ciliary muscle contractility, or accommodative response to a 4 D near target.

Quantification of age-related and per diopter accommodative changes of the lens and ciliary muscle in the emmetropic human eye

PURPOSE

To calculate age-related and per diopter (D) accommodative changes in crystalline lens and ciliary muscle dimensions in vivo in a single cohort of emmetropic human adults ages 30 to 50 years.

METHODS

The right eyes of 26 emmetropic adults were examined using ultrasonography, phakometry, anterior segment optical coherence tomography, and high resolution magnetic resonance imaging. Accommodation was measured both subjectively and objectively.

RESULTS

In agreement with previous research, older age was linearly correlated with a thicker lens, steeper anterior lens curvature, shallower anterior chamber, and lower lens equivalent refractive index (all P < 0.01). Age was not related to ciliary muscle ring diameter (CMRD) or lens equatorial diameter (LED). With accommodation, lens thickness increased (+0.064 mm/D, P < 0.001), LED decreased (-0.075 mm/D, P < 0.001), CMRD decreased (-0.105 mm/D, P < 0.001), and the ciliary muscle thickened anteriorly (+0.013 to +0.026 mm/D, P < 0.001) and thinned posteriorly (-0.011 to -0.015, P < 0.01). The changes per diopter of accommodation in LED, CMRD, and ciliary muscle thickness were not related to subject age.

CONCLUSIONS

The per diopter ciliary muscle contraction is age independent, even as total accommodative amplitude declines. Quantifying normal biometric dimensions of the accommodative structures and changes with age and accommodative effort will further the development of new IOLs designed to harness ciliary muscle forces.

Changes in ciliary muscle thickness during accommodation in children

PURPOSE

To investigate the morphology of the ciliary muscle during the act of accommodation in a population of children.

METHODS

Thirty children aged 6 to 12 years were enrolled. Accommodative response was measured through habitual correction. Height was measured as a control variable. Central axial length was measured with the IOLMaster. Four images of the temporal ciliary muscle were taken with the Visante Optical Coherence Tomographer at three different stimulus levels (0, 4, and 6 D) while accommodative response was monitored concurrently with the PowerRefractor. Accommodative response monitoring was time-matched to ciliary muscle image capture, and the mean was calculated for 5 s surrounding this time point. Four cycloplegic images of the temporal ciliary muscle were also taken. Ciliary muscle thickness measurements were made at the point of maximum thickness (CMTMAX) and at 1 mm (CMT1), 2 mm (CMT2) and 3 mm (CMT3) posterior to the sclera spur.

RESULTS

Increasing accommodative response was correlated with increases in the thickness of CMTMAX (p = <0.001) and CMT1 (p = <0.001) and decreases in the thickness of CMT3 (p = <0.001). Thicker values of CMTMAX under cycloplegic conditions were significantly correlated with values of CMTMAX (p = <0.001) and CMT1 (p = 0.001) while accommodating and approached significance in modeling CMT3 (p = 0.06). Mean axial length was correlated with the amount of thinning at CMT3 with accommodation (p = 0.002). Axial length was not significantly correlated with thickness values at CMTMAX (p = 0.7) or CMT1 (p = 0.6).

CONCLUSIONS

In a manner similar to previous adult studies, ciliary muscle thickness at CMTMAX and CMT1 increased with accommodation and CMT3 thinned with accommodation. Further investigation is necessary to determine whether CMT2 is a "fulcrum" point along the length of the ciliary muscle where the net change with accommodation is always zero or whether that point varies across subjects or with varying levels of accommodative effort.

Measuring changes in ciliary muscle thickness with accommodation in young adults

PURPOSE

To develop a measurement protocol for changes in the shape and size of the ciliary muscle with accommodation using the Zeiss Visante™ anterior segment optical coherence tomography (AS-OCT) and to determine the test-retest repeatability of these measurements.

METHODS

Subjects were 25 adults aged 23 to 28 years. The ciliary muscle was imaged at two visits with the Visante™ while accommodative response was monitored during imaging using the PowerRefractor. Ciliary muscle thickness (CMT) was measured at 1 mm (CMT1), 2 mm (CMT2), and 3 mm (CMT3) posterior to the scleral spur and at the point of maximal thickness (CMTMAX). Thickness was measured at these locations while subjects viewed a target at distance and at a 4.00 D accommodative stimulus. Outcome measures were the change in thickness between distance and the 4.00 D stimulus and the change in thickness per diopter of accommodative response (PowerRefractor). Finally, the repeatability measurements between visit 1 and visit 2 were determined with a Bland-Altman analysis.

RESULTS

The statistically significant modeled changes in CMT were as follows: CMTMAX = 69.2 μm (4.00 D stimulus) and 18.1 μm (per diopter of accommodation); CMT1 = 45.2 μm (4.00 D stimulus) and 12.3 μm (per diopter of accommodation); and CMT3 = -45.9 μm (4.00 D stimulus) and -12.0 μm (per diopter of accommodation); p < 0.0001 for all.

CONCLUSIONS

The combination of the Visante™ and the PowerRefractor is a feasible tool for measuring thickening of ciliary muscle at more anterior locations and thinning at more posterior locations during accommodation. We noted a wide range of accommodative responses during the time of image capture in this study indicating that the most accurate estimates of the change in ciliary muscle dimensions with accommodation may be obtained by using accommodative response rather than stimulus values and by using measurements taken simultaneously with image capture.