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

Assessment of the ciliary muscle and scleral anterior thickness in high myopia by optical coherence tomography

PURPOSE

To assess ciliary muscle (CM) and anterior scleral thickness (AST) dimensions in vivo in high myopia using swept-source optical coherence tomography (SS-OCT) and to compare with emmetropic and hyperopic subjects.

METHODS

Cross-sectional study that included 34 high myopic patients (≥ -6 diopters [D]), 90 emmetropes (-1 to +1 D) and 38 hyperopic patients (≥ +3.5 D). CM thickness (CMT) and AST were measured in the temporal and nasal quadrants at 1, 2, and 3 mm from the scleral spur using SS-OCT. In addition, the length of the CM (CML) was evaluated.

RESULTS

The dimensions of the CML and the CMT at any of their measurement points were greater in high myopes and emmetropes than in hyperopes, both in the nasal and temporal quadrants (P < .001). However, there were no differences between high myopes and emmetropes for any of the parameters (P ≥ .076) except for the CMT at 3 mm in the temporal quadrant (P < .001). There were no differences in the AST between high myopes, emmetropes and hyperopes, in any of the measurement points or quadrants studied (P > .05).

CONCLUSIONS

The SS-OCT allows to measure the CM in vivo, not observing differences in its dimensions between high myopes and emmetropes, but they were smaller in hyperopes. In the measurement of the anterior sclera, no differences were observed between the three groups analyzed according to refraction.

Comparison in conjunctival-Tenon's capsule thickness, anterior scleral thickness and ciliary muscle dimensions between Caucasians and Hispanic by optical coherence tomography

PURPOSE

To investigate the differences in the dimensions of the anterior ocular segment, and specifically in conjunctival-Tenon's capsule thickness (CTT), anterior scleral thickness (AST) and ciliary muscle thickness (CMT), between Caucasian and Hispanic subjects using swept-source optical coherence tomography (SS-OCT).

METHODS

Cross-sectional study including 53 Hispanic and 60 Caucasian healthy participants, matched by age, sex and refractive error, who underwent a complete ophthalmological examination. CTT, AST and CMT were manually measured in the temporal and nasal quadrants at 0, 1, 2 and 3 mm from the scleral spur using SS-OCT.

RESULTS

Mean age and refractive error were 38.7 ± 12.3 years and -1.05 ± 2.6 diopters, and 41.8 ± 11.7 years and -0.50 ± 2.6 diopters for the Hispanic and Caucasians, respectively (p = 0.165 and p = 0.244). The CTT was increased in the temporal quadrant in the Hispanic group in the three studied regions (CTT1, CTT2 and CTT3; being the means 223.0 ± 68.4, 215.3 ± 66.4 and 203.8 ± 67.1 µm versus 190.8 ± 51.0, 189.4 ± 53.2 and 187.4 ± 55.3 µm respectively; p < 0.001). Larger AST values were observed in the temporal quadrant in the Hispanic group (AST2: 559.8 ± 80.8 µm and AST3: 591.6 ± 83.0 µm) compared to the Caucasian group (520.7 ± 50.1 and 558.9 ± 54.7 respectively; p ≤ 0.022). No differences were observed in the nasal quadrant for CTT, AST1 and AST3 (p ≥ 0.076). No differences emerged in the CM dimensions (p ≥ 0.055).

CONCLUSION

CTT and AST measurements were thicker in the temporal quadrant of Hispanic patients compared to Caucasians. This could have implications for the pathogenesis of different ocular diseases.

New technology using crystalline lens autofluorescence for presbyopia and cataract grading

PURPOSE

To investigate  whether fundus autofluorescence (FAF) obtained using an ultra-wide field (UWF) fundus camera with an artificial opacity pattern can grade the degree of presbyopia and nuclear cataract.

METHODS

Sixty eyes of 30 patients were enrolled in this prospective diagnostic study. The nuclear cataract (nuclear color/opalescence (NC/NO)) was graded according to the Lens Opacity Classification System III. The monocular near point of accommodation (NPA) was measured in eyes with NC3/NO3 or less. The mean gray value difference between the central 8 artificial opacity lesions and peripheral 8 artificial opacity lesions in the retinal AF was measured. The correlation between the mean gray value difference, NPA, and nuclear cataract grade was analyzed.

RESULTS

The mean nuclear cataract grade of 60 eyes was 3.2 ± 1.6 and mean NPA of 37 eyes was 45.3 ± 16.1 cm. The mean gray value differences increased with increasing nuclear cataract grade (eyes with NC/NO grade 1, 53.3 ± 11.4; 2, 78.3 ± 13.6; 3, 95.2 ± 12.2; 4, 101.6 ± 11.9; 5, 109.0 ± 22.9; and 6, 121.1 ± 12.0; p < 0.001). The mean gray value difference was positively correlated with both the monocular NPA (R² = 0.637; β coefficient = 1.009; 95% CI, 0.748 to 1.271; p < 0.001) and nuclear cataract grade (R² = 0.661; β coefficient = 12.437; 95% CI, 10.097 to 14.778; p < 0.001).

CONCLUSIONS

The FAF camera with an artificial opacity pattern attached can be used to effectively diagnose the degree of presbyopia and nuclear cataract.

Pharmacological Treatments for Presbyopia

Accommodation is the change in dioptric power of the eye. It is a dynamic process that allows focusing on an object at all distances. In order to focus sharply, three physiological responses, known as the triad of accommodation, are produced by a change in pupil size, a change in shape and position of the lens, and ocular convergence. This is modulated by the autonomic nervous system, mainly the parasympathetic nervous system. Presbyopia is a refractive condition that occurs with aging, usually manifesting around 40-50 years of age, and is a result of the loss of accommodation in the eye, causing loss of visual performance when focusing on objects placed at different distances, starting with near vision. Glasses, contact lenses, surgical approaches and now pharmacological treatments are accepted methods of treating presbyopia. Pharmacological treatment is a promising new noninvasive option for treating presbyopia. Currently there are three pharmacological approaches to the treatment of presbyopia. The first one aims to produce miosis and, from a pinhole effect, increase depth of focus, and therefore improve uncorrected near visual acuity (UNVA). The second one addresses rehabilitating accommodation in a binocular way, allowing good vision at all distances. Finally, the third strategy uses lipoic acid to restore the lost elasticity of the lens. All of these pharmacological treatments are topical non-invasive eyedrops, with no serious adverse effects having been reported with any of the strategies, and require the right patient selection process to fulfill expectations and needs. The aim of this article is to provide an update on recent advances in this field.

Design of an Automatically Controlled Multi-Axis Stretching Device for Mechanical Evaluations of the Anterior Eye Segment

The young eye has an accommodative ability involving lens shape changes to focus over different distances. This function gradually decreases with age, resulting in presbyopia. Greater insights into the mechanical properties of anterior eye structures can improve understanding of the causes of presbyopia. The present study aims to develop a multi-axis stretching device for evaluating the mechanical properties of the intact eye lens. A stretching device integrating the mechanical stretcher, motor, torque sensor and data transmission mechanism was designed and developed by 3D printing. The mechanical stretcher can convert rotation into radial movement, both at constant speeds, according to the spiral of Archimedes. The loading unit equipped with eight jaws can hold the eye sample tightly. The developed device was validated with a spring of known constant and was further tested with anterior porcine eye segments. The validation experiment using the spring resulted in stiffness values close to the theoretical spring constant. Findings from measurements with porcine eye samples indicated that the measured forces are within the ranges reported in the literature. The developed multi-axis stretching device has good repeatability during experiments with similar settings and can be reliably used for mechanical evaluations of the intact eye lens.

In vivo analysis of ciliary muscle in myopic Chinese young adults using ArcScan Insight® 100

OBJECTIVE

To analyse the morphological characteristics of the ciliary muscle (CM) and to explore its relationship with different ocular biometric parameters in myopic young Chinese adults.

METHODS

This observational, cross-sectional study included 50 right eyes from 50 myopic adults. The CM area (CMA), CM thickness (CMT) and CM length (CML) were measured using the ArcScan Insight^® 100. CMT was determined at three points: 1.0 mm (CMT-1), 2.0 mm (CMT-2) and 3.0 mm (CMT-3) posterior to the scleral spur. CML was measured on the scleral (CMLs) and vitreous (CMLv) aspects. The spherical equivalent refraction (SER), axial length (AL) and subfoveal choroidal thickness (SFCT) were examined to determine their associations with CM parameters (CMA, CML and CMT).

RESULTS

The mean SER and AL were -4.39 ± 2.29 D and 25.61 ± 1.15 mm, respectively. Compared with the nasal CMA, CML and CMT (CMT-1, CMT-2 and CMT-3) findings, the temporal CM parameters (CMA, CMLs, CMLv, CMT-1, CMT-2 and CMT-3) were found to be significantly thicker (all p < 0.001, except CMLv and CMT-1; p < 0.01). The nasal CMA was associated with the average corneal curvature (r = 0.30, p = 0.03) and SER (r = -0.30, p = 0.04). Nasal and temporal CMT-2 were negatively correlated with SER (r = -0.33 and -0.32, respectively, both p < 0.05). There was no correlation between CM parameters (except nasal CMLs, r = 0.31, p = 0.03) and SFCT, or between CM parameters and either the AL or anterior chamber depth (all p > 0.05).

CONCLUSION

These results suggest that there is temporal versus nasal asymmetry of the CM. CMA, CMT or CML did not vary with axial growth of the eye. The CM is not simply stretched as the eye elongates in myopic young adults.

[Anatomical, morphological and biomechanical aspects of accommodation]

The article reviews the findings on the anatomy, morphological and biomechanical features of the accommodation apparatus. Modern methods of imaging and biometry confirm the validity of the Helmholtz lenticular theory of accommodation, according to which its mechanism involves three main components: the ciliary body, the zonular fibres and the lens capsule, the lens itself. Based on this, there is certain interest in studying the degree of participation of each of these components in the development of age-related changes in accommodation (presbyopia).

Assessing accommodative presbyopic biometric changes of the entire anterior segment using single swept-source OCT image acquisitions

BACKGROUND/OBJECTIVES

To evaluate biometric changes throughout the anterior chamber during accommodation and presbyopia using single image acquisition swept-source anterior-segment optical coherence tomography (AS-OCT).

SUBJECT/METHODS

Anterior-segment images were obtained using a new swept-source AS-OCT device (ANTERION, Heidelberg Engineering) from healthy volunteers (n = 71) across two centers in this prospective observational case series. In one image acquisition, cornea through posterior lens, including the ciliary muscle on both sides of the right eye, was imaged. Subjects undertook no accommodative effort and -1, -3, and -5 D of target vergence. Two-way repeated measures ANOVA modeling was performed for ciliary muscle measurements, lens parameters, aqueous depth (AD), and pupil diameter (PD). The first ANOVA factor was accommodative stimuli, and the second factor included age and refractive status.

RESULTS

Maximum ciliary muscle thickness increased with accommodative stimuli (p < 0.001), while the distance from the scleral spur to the maximal point on the ciliary muscle and posterior ciliary muscle thickness (CMT2) decreased (p < 0.001-0.002). Older individuals showed no accommodative changes for ciliary muscle parameters, lens thickness, lens vault, PD, and AD (p = 0.07-0.32). Younger- and middle-aged eyes showed statistically significant accommodative structural alterations for these endpoints (p < 0.001-0.002), but with different patterns, including early loss of CMT2 contraction in middle-aged eyes. Within the middle-aged group, myopic eyes maintained better capacity for accommodative structural change.

CONCLUSIONS

Swept-source AS-OCT demonstrated multiple simultaneous anterior-segment biometric alterations in single acquisition images, including early loss of posterior ciliary muscle function and better maintained capacity for anterior-segment structural change in myopia.

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.

Digitized mini optofluidic element and its application to ophthalmic lenses for presbyopia correction

Using the internally placed elastic membrane and multi-chamber configuration, we designed a digitized mini optofluidic element for fast switching between refractive and diffractive states of preset optical powers. Relief surface was used in the diffractive state. We applied finite element analysis to establish membrane mechanical characteristics for switching at the force level produced by the ocular elements such as ciliary muscle or lower eyelid at eye downgaze. The prototypes were made to demonstrate proof-of-concept. Membrane conformance to the diffractive grooves and imaging quality were demonstrated. The analysis supported switching under the force level exerted by the ocular elements supporting the digitized optofluidic element potential for presbyopia correction by ophthalmic lenses.

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.