Morphometric assessment of normal human ciliary body using ultrasound biomicroscopy

Cyclodestruction and cyclophotocoagulation: Where are we?

Cyclodestruction is a technique reserved for glaucomas not controlled with medical and surgical treatment and poor visual potential. During the last century, new cyclodestructive techniques were developed, including cyclophotocoagulation, and the use of continuous-wave diode laser transescleral cyclophotocoagulation (CW-TS-CPC) has become widespread. In recent decades, micropulse diode laser transescleral cyclophotocoagulation (MP-TS-CPC) was introduced. We review the cyclodestruction techniques since their origins and these two techniques of cyclophotocoagulation, which are currently the most widely used: how they are performed, their mechanisms of action and their effectiveness and efficacy. We also review the comparison between them and with other techniques.

Morphometric Assessment of Sclera and Ciliary Body in Patients with Noninfectious Anterior Scleritis: A Quantitative Study Using Ultrasound Biomicroscopy

BACKGROUND

At present, the severity and grade of anterior scleritis are judged mainly based on the area and location of involvement, whether there is necrosis, etc. Quantitative measurement of sclera and surrounding tissues will help to accurately assess the severity of scleritis and provide quantitative indicators for the choice of treatment.

METHODS

We retrospectively analyzed the thickness of sclera and ciliary bodies detected by ultrasound biological microscopy (UBM) in noninfectious anterior scleritis patients who subsequently were treated with topical or systemic treatment, and visited our hospital from March 2014 to March 2021. Age- and sex-matched normal individuals were used as controls.

RESULTS

A total of 185 patients (50 males and 135 females) with noninfectious anterior scleritis and 84 (31 males and 53 females) controls were included. In patients with noninfectious scleritis, the thickness of sclera and the ciliary body were significantly greater than those in the control group (p < 0.05). Before treatment, the thickness of sclera and the ciliary body in systemic treatment group was significantly higher than that in topical treatment group (p < 0.05). After treatment, both thicknesses of sclera and the ciliary body decreased significantly (p < 0.05). The ratio of ciliary body thickness from the site of inflammation to the normal position was significantly higher in the systemic treatment group than in the topical treatment group.

CONCLUSIONS

UBM quantitatively shows a decrease in AST/CBT in patients with anterior scleritis after treatment. The ratio of ciliary body thickness at the site of information to that at the normal position may be a reference for the choice of treatment.

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.

Characteristics of ciliary muscle profile in high myopes measured by swept-source anterior segment optical coherence tomography

OBJECTIVE

To characterize and compare the ciliary muscle thickness (CMT) between low and high myopes using swept-source anterior segment optical coherence tomography (AS-OCT).

METHODS

Forty visually healthy young Chinese adults aged 18-25 years were divided into two groups based on refractive errors: low myopia (n = 20, spherical-equivalent refractive error (SER) between -0.50 D to -3.00 D) and high myopia (n = 20, SER ≤ -6.00 D). Cycloplegic refractions were performed before axial length (AL) and CMT were measured using a partial coherence laser interferometer and an AS-OCT respectively. CMT was measured perpendicularly to the sclera-ciliary muscle interface at 1 mm (CMT_1), 2 mm (CMT_2), and 3 mm (CMT_3) posterior to the scleral spur, and at the location with maximal thickness (CMT_MAX).

RESULTS

High myopes demonstrated thicker CMT at 2 mm (CMT_2, p = 0.035) and 3 mm (CMT_3, p = 0.003) posterior to the scleral spur, but thinner maximal CMT (CMT_MAX, p = 0.005) than low myopes. The apical CMT_1 and CMT_MAX were also thinner in high myopes than in low myopes (both p< 0.001). CMT_MAX, apical CMT_1, and apical CMT_MAX correlated directly with SER and inversely with AL; in contrast, CMT_2 and CMT_3 showed inverse correlations with SER but direct correlations with AL.

CONCLUSION

Our findings revealed significant differences in CMT between low and high myopes, with high myopes showing thicker CMT at 2 mm and 3 mm posterior to the scleral spur, but thinner maximal CMT. These results provide new evidence of the potential structural differences in ciliary muscles during myopia development and progression.

Evaluating spatial dependency of the spectral efficiency in trans-palpebral illumination for widefield fundus photography

Multi-spectral widefield fundus photography is valuable for the clinical diagnosis and management of ocular conditions that may impact both central and peripheral regions of the retina and choroid. Trans-palpebral illumination has been demonstrated as an alternative to transpupillary illumination for widefield fundus photography without requiring pupil dilation. However, spectral efficiency can be complicated due to the spatial variance of the light property through the palpebra and sclera. This study aims to investigate the effect of light delivery location on spectral efficiency in trans-palpebral illumination. Four narrow-band light sources, covering both visible and near infrared (NIR) wavelengths, were used to evaluate spatial dependency of spectral illumination efficiency. Comparative analysis indicated a significant dependence of visible light efficiency on spatial location, while NIR light efficiency is only slightly affected by the illumination location. This study confirmed the pars plana as the optimal location for delivering visible light to achieve color imaging of the retina. Conversely, spatial location is not critical for NIR light imaging of the choroid.

Morphometric assessment of the ciliary body in patients with Marfan syndrome and ectopia lentis: A quantitative study using ultrasound biomicroscopy: Ciliary body morphology in Marfan syndrome and ectopia lentis

PURPOSE

To explore the biometric characteristics of the ciliary body in patients with Marfan syndrome (MFS) and ectopia lentis (EL).

DESIGN

Cross-sectional study.

METHODS

Seventy-two consecutive MFS patients with EL and 72 non-disease controls were recruited. Ciliary body biometric parameters such as ciliary muscle cross-sectional area at 2000 μm from the scleral spur (CMA2000), ciliary muscle thickness at 1000 μm from the scleral spur (CMT1000), and maximum ciliary body thickness (CBTmax) were measured from multiple directions with ultrasound biomicroscopy (UBM). The relationship between ciliary body parameters and other ocular characteristics was also evaluated.

RESULTS

Average CMA2000, CMT1000, and CBTmax were 0.692 ± 0.015 mm², 0.405 ± 0.010 mm, and 0.855±0.023 mm in MFS eyes, respectively, and were significantly smaller than controls (all p < 0.001). The prevalence of ciliary body thinning was 22.2% in the MFS group versus 0 in controls (p < 0.001); eyes with more severe EL had smaller CMA2000 (p = 0.050), thinner CMT1000 (p = 0.022) and shorter CBTmax (p = 0.015). Patients with microspherophakia (MSP) had even smaller CMA2000 (p = 0.033) and CMT1000 (p = 0.044) than those without MSP. The most common subluxation direction was in the superonasal quadrant (25, 39.7%), which probably correlates with the thinnest CMT1000 in the inferotemporal quadrant (p = 0.005).

CONCLUSIONS

MFS patients with EL had thinner ciliary muscles, shorter ciliary processes, and a higher prevalence of ciliary body thinning, especially those with MSP. Both the extent and direction of subluxation were associated with ciliary body biometry.

Characteristics of the Ciliary Body in Healthy Chinese Subjects Evaluated by Radial and Transverse Imaging of Ultrasound Biometric Microscopy

Background: The imaging and analysis of the ciliary body (CB) are valuable in many potential clinical applications. This study aims to demonstrate the anatomy characteristics of CB using radial and transverse imaging of ultrasound biometric microscopy (UBM) in healthy Chinese subjects, and to explore the determining factors. Methods: Fifty-four eyes of 30 healthy Chinese subjects were evaluated. Clinical data, including age, body mass index (BMI), intraocular pressure (IOP), axial length (AL), and lens thickness (LT), were collected. Radial and transverse UBM measurements of the ciliary body were performed. Anterior chamber depth (ACD), ciliary sulcus diameter (CSD), ciliary process length (CPL), ciliary process density (CPD), ciliary process area (CPA), ciliary muscle area (CMA), ciliary body area (CBA), ciliary body thickness (CBT0, CBT1, and CBTmax), anterior placement of ciliary body (APCB), and trabecular-ciliary angle (TCA) of four (superior, nasal, inferior, and temporal) quadrants were measured. Results: The average CPL was 0.513 ± 0.074 mm, and the average CPA was 0.890 ± 0.141 mm2. CPL and CPA tended to be longer and larger in the superior quadrant (p < 0.001) than in the other three quadrants. Average CPL was significantly correlated with AL (r = 0.535, p < 0.001), ACD (r = 0.511, p < 0.001), and LT (r = −0.512, p < 0.001). Intraclass correlation coefficient (ICC) scores were high for CPL (0.979), CPD (0.992), CPA (0.966), CMA (0.963), and CBA (0.951). Conclusions: In healthy Chinese subjects, CPL was greatest in the superior quadrant, followed by the inferior, temporal, and nasal quadrants, and CPA was largest in the superior quadrant, followed by the tempdoral, inferior, and nasal quadrants. Transverse UBM images can be used to measure the anatomy of the ciliary process with relatively good repeatability and reliability.

Imaging of the Ciliary Body: A Major Review

PURPOSE

We conducted a systematic search of literature to understand the various methods of imaging of the ciliary body.

METHODS

PubMed, Science Direct, Cochrane Library and Google Scholar were searched comprehensively and systematically to find studies related to the various modalities of ciliary body imaging.

RESULTS

The various ciliary body parameters that have been described are Ciliary body thickness, Ciliary body length, ciliary muscle thickness, ciliary process length, ciliary muscle length, ciliary muscle anterior length, trabecular ciliary process distance and Iris ciliary process distance. The various angles which have been measured, which mostly have a significance in Primary angle closure glaucoma (PACG) are Iris ciliary angle, Trabecular ciliary angle, scleral ciliary process angle. Various authors have defined them in various ways with subtle differences. Plateau iris and PACG mechanisms, not forgetting malignant glaucoma are better understood with imaging of the ciliary body using the ultrasound biomicroscopy (UBM). The anterior segment optical coherence tomography (ASOCT) imaging of the ciliary body has been described albeit with its own disadvantages. A few other fields dependant on the importance of ciliary body imaging are intravitreal injections, pars plana vitrectomy, measurements for implantable collamer lens (ICL) and of utmost importance, the differentiating features of ciliary body masses.

CONCLUSION

The UBM is still preferred over the ASOCT for imaging of the ciliary body. A lot of lacunae of knowledge still exists and consensus has to be reached on defining all the parameters universally. Future studies will be able to shed more light on the role of the ciliary body in the many ocular disorders mentioned in this review.

Changes After a Month Following Micropulse Cyclophotocoagulation in Normal Porcine Eyes

Purpose

To analyze the effects on the uvea, including the pars plicata and ciliary muscle, and retina in normal porcine eyes after performing micropulse transslceral cyclophotocoagulation (MP-TSCPC) with the different energy levels, and conventional continuous wave transslceral cyclophotocoagulation.

Methods

MP-TSCPC was performed in a total of 15 eyes at the different energy levels of 60 J, 120 J, 180 J, 240 J, and 300 J, respectively. Continuous wave transslceral cyclophotocoagulation was performed in three eyes and the other three eyes were controls. The eyes were enucleated after a month following the laser treatment and the uvea and retina were analyzed using hematoxylin and eosin staining and immunohistochemistry staining.

Results

After MP-TSCPC 60 J, the expression of α-smooth muscle actin (α-SMA) and glial fibrillary acidic protein in the ciliary muscle was increased, although there was no structural change in pars plicata. After MP-TSCPC 120 J, partial destruction of the ciliary epithelium was observed in pars plicata, and the retinal thickness was increased. After MP-TSCPC 240 J and 300 J, the structural destruction of the pars plicata and ciliary muscle was observed, and the expression of α-SMA and glial fibrillary acidic protein in pars plicata and the expression of α-SMA in ciliary muscle were increased.

Conclusions

Histologic changes in the uvea and peripheral retina were different based on the energy levels of MP-TSCPC. In particular, MP-TSCPC with low energy levels mainly affected the ciliary muscle, while MP-TSCPC with high energy levels affected both the ciliary muscle and pars plicata. Our results may imply a possibility of intraocular damage with MP-TSCPC in humans.

Translational Relevance

Based on our research, it is possible to infer the possibility of intraocular damage in humans according to the different levels of energy in the clinic.

Efficacy, Safety, and Retreatment Benefit of Micropulse Transscleral Cyclophotocoagulation in Glaucoma

PRECIS

Micropulse transscleral cyclophotocoagulation (MP-TSCPC) with a 120-second setting reduces intraocular pressure (IOP) with a 6-month success of 45.5%. Only late (>6 mo) failure seem to present a benefit for retreatment.

PURPOSE

The purpose of this study was to assess MP-TSCPC efficacy, safety, factors of success, and retreatment benefit in open-angle glaucoma.

PATIENTS AND METHODS

A retrospective consecutive case series study. We included patients with open-angle glaucoma who were naive of a cycloablative procedure and underwent MP-TSCPC at 2000 mW for 120 seconds between May 1, 2017, and October 31, 2019. Success was defined as IOP >5 and ≤21 mm Hg with IOP reduction ≥20% from baseline, without any retreatment and visual acuity better than negative light perception. MP-TSCPC retreatment was early and late, before and after 6 months postoperatively, respectively.

RESULTS

We included 94 eyes in 94 patients [mean (SD) age: 67.2 (13.4) y; 47.9% women]. The mean preoperative IOP was 24.9 (7.1) mm Hg and was reduced to 18.9 (6.3) at month 6 (P<0.0001). The success rate decreased progressively over time and reached 45.5% at 6 months. Patients with 6-month surgical success had lower mean axial length than others [24.1 (1.5) vs. 25.5 (2.1) mm, P=0.05]. In patients with early and late MP-TSCPC retreatment, the 6-month success rate was 16.7% and 63.6%, respectively.

CONCLUSIONS

MP-TSCPC performed with a 120-second setting reduced IOP, with 45.5% success at month 6 and few complications. Axial length was newly described as affecting success, probably linked to the ciliary-body position. Retreatment seemed to be of little benefit in nonresponders or those with early failure. Further studies on laser settings and ciliary-body location are required to find the best risk-benefit protocol.

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.

Clinical 3D Imaging of the Anterior Segment With Ultrasound Biomicroscopy

Purpose

Ultrasound biomicroscopy (UBM) is an important ophthalmic imaging modality due to its ability to see behind pigmented iris and to visualize anterior chamber when the eye's transparency is compromised. We created a three-dimensional UBM (3D-UBM) system and acquired example images to illustrate its potential.

Methods

A commercial 50-MHz two-dimensional UBM (2D-UBM) system was attached to a precision translation stage and translated across the eye to acquire an image volume. The stage was mounted on a surgical microscope, which enabled safe, stable positioning. Image processing steps included image alignment, noise reduction, and calibration. 3D visualization included alignment of the optic axis, multiplanar reformatting at arbitrary orientations, and volume rendering with optimized transfer functions. Scans were performed on cadaver and rabbit eyes.

Results

3D-UBM allowed visualization of the anterior segment tissues within a 3D anatomical context, unlike 2D-UBM. En face views and interactive slicer operations suggested an ability to plan and assess treatments, including lens placement and microcatheter cannulation of Schlemm's canal. Interactive software allowed us to make accurate measurements of tissue structures (e.g., iridocorneal angles, cyst volumes). In addition, unique measurements of ciliary tissues included single ciliary process volumes of 0.234 ± 0.093 mm³ with surface areas of 3.02 ± 1.07 mm² and ciliary muscle volume of 67.87 mm³.

Conclusions

3D-UBM imaging of the anterior segment can be used to enable unique visualization and quantification of anterior segment structures.

Translational Relevance

3D-UBM provides informative 3D imaging of tissues in the eye that are invisible to light to potentially provide physicians with improved diagnosis, treatment planning, and treatment assessment as compared to conventional 2D-UBM.

Anterior scleral thickness dimensions by swept-source optical coherence tomography

Clinical relevance: Given the association of scleral characteristics with many ophthalmological diseases, there is an important need to measure the anterior scleral thickness (AST).Background: This study examined the AST by swept-source optical coherence tomography (SS-OCT) in a large healthy population, assessing also the reproducibility of AST measurements and the correlation with different parameters.Methods: Cross-sectional study in 605 eyes of 605 subjects. AST measurements were made in the temporal and nasal quadrants at 1 (AST1) and 3 mm (AST3) from the scleral spur using SS-OCT. These dimensions were then assessed for associations in a multivariate model with the factors age, sex, refractive error, conjunctival-Tenon capsule thickness (CTT), anterior chamber angle (ACA), intraocular pressure (IOP), iris thickness (IT), limbus-sulcus distance (LSD), and ciliary muscle thickness (CMT). The reproducibility of the AST measurements was determined in 30 of the participants.Results: The mean age was 42.6 ± 17.3 years (range 5 to 86 years). The following means were recorded: AST1 was 522.3 ± 65.7 µm (355 to 761) and 558.4 ± 71.5 µm (357 to 889); AST2 was 513.3 ± 67.3 µm (343 to 732) and 574.4 ± 71.6 µm (389 to 789), and AST3 548.8 ± 71.9 µm (356 to 762) and 590.1 ± 76.6 µm (414 to 873) in the temporal and nasal quadrants respectively, being thicker the nasal quadrant (all p < 0.001). A positive correlation was detected between AST and age, sex, temporal ACA and LSD (all p ≤ 0.043), being negative the correlation with CMT (p ≤ 0.044). No correlation was observed between AST measurements and refractive error, CTT and IT (p ≥ 0.064). The reproducibility of AST measurements was excellent (intraclass correlation coefficient ≥0.951).Conclusions: SS-OCT allows for in vivo AST measurements. Our data contained a wide range of measurements, showing an association between AST and age, sex, ACA, LSD and CMT.

Modeling of the increased intraocular pressure effect on changes in the stress state of the eyeball’s internal structures

The aim of the study was creating a model and evaluating the effect of elevated IOP in the anterior chamber during phacoemulsification on the changes in the stress state of various ocular structures. Materials and methods.A simplified axial symmetrical anatomical model of the eyeball was created using the finite element method. Using the Deform software package, the deformation problem was worked out by calculating the redistribution of the excess pressure in the anterior chamber during phacoemulsification, on the changes in the stress state of different ocular structures.Results. At processing of modeling results, data were obtained on redistribution of the excess pressure delivered to the anterior chamber towards its decrease in the posterior pole area. The pressure level amounted to 0.85 % of excess pressure applied. The findings are supported by few animal experiments. Conclusions.Proposed model of the increased IOP level effect on changes in the stressed state of various ocular structures demonstrates that the autoregulation mechanism maintaining ocular blood flow at a constant level includes a compensating mechanism for a steep IOP increase due to elastic properties of the vitreous body. This model allows calculating the redistribution of pressure in different parts of the eyeball, depending on the state of resilient-elastic properties of the vitreous, as well as on avitreal eyes, and in patients with silicone oil tamponade.

Does anisometropia affect the ciliary muscle thickness? An ultrasound biomicroscopy study

PURPOSE

To compare the ciliary muscle thickness (CMT) of the normal fellow eye to that of the amblyopic eye using ultrasound biomicroscopy (UBM) in patients with unilateral anisometropic amblyopia.

METHODS

Thirty patients with unilateral anisometropic amblyopia were involved. The patients were divided into two groups: 19 hyperopic and 11 myopic. Axial length (AL) was measured with optic biometry and anterior chamber depth (ACD), iris area, and CMT were measured with UBM.

RESULTS

The mean age was 34.10 ± 6.61 years. The mean spherical difference between two eyes was 2.59 diopter (D) in hyperopic patients and 3.77D in myopic patients. In the hyperopic patients, nasal CMT1(nCMT), temporal CMT1(tCMT), tCMT2, and tCMT3 values were statistically thinner in amblyopic eyes than healthy eyes (p = 0.036, p = 0.003, p = 0.023, p = 0.005, respectively). ACD values were statistically lower in amblyopic eyes (2.78 ± 0.26 mm) than healthy eyes (2.90 ± 0.21 mm) (p < 0.001). In the myopic patients, nCMT1, nCMT2, nCMT3, tCMT1, tCMT2, and tCMT3 values were statistically thicker in amblyopic eyes than healthy eyes (p = 0.003, p = 0.003, p = 0.005, p = 0.003, p = 0.003, p = 0.019, respectively). ACD values were statistically higher in amblyopic eyes (3.20 ± 0.30 mm) than healthy eyes (3.06 ± 0.29 mm) (p = 0.004). Also, there was no significant difference in the iris area between the amblyopic and normal eyes of the myopic and hyperopic patients (p > 0.05).

CONCLUSIONS

Amblyopic eyes in patients with unilateral myopic anisometropia have thicker CMT and deeper ACD than healthy eyes. Conversely, amblyopic eyes in patients with unilateral hyperopic anisometropia have thinner CMT and shorter ACD than healthy eyes. There is a positive correlation between AL and CMT.

Ciliary body length revisited by anterior segment optical coherence tomography: implications for safe access to the pars plana for intravitreal injections

Purpose

To investigate the dependence of the ciliary body length (CBL) on the axial length (AL) and to draw conclusions on implications regarding safe pars plana access for intravitreal injections and vitreoretinal surgery.

Methods

A total of 200 individuals (mean age 42 years, SD ± 15.4) were enrolled in the study. Objective refraction and AL were obtained. Spherical equivalent (SE) was calculated. Anterior segment optical coherence tomography (ASOCT) was used to image and measure the CBL.

Results

The mean SE was − 1.64 diopters (SD ± 3.15, range − 14.5 to + 9 diopters) and the mean AL was 24.19 mm (SD ± 1.65, range 19.8–32.2 mm). There was a significant correlation between SE and AL (r² = 0.62, p < 0.0001). Mean CBL correlated significantly with age (r² = 0.11, p < 0.0001), AL (r² = 0.23, p < 0.0001) and SE (r² = 0.25, p < 0.0001). The mean CBL was 3351 μm (SD ± 459, range 2184–4451 μm). Three separate groups were defined by their AL with a normal AL group (AL 22.5 to 25 mm), a short AL group (AL < 22.5 mm) and a long AL group (AL > 25 mm). The mean CBL in the normal AL group was 3311 μm (SD ± 427), in the short AL group 2936 μm (SD ± 335) and in the long AL group 3715 μm (SD ± 365), and differed significantly (p < 0.0001) when compared.

Conclusion

For interventions requiring pars plana access (as an intravitreal injection or vitreoretinal surgery), an incision distance of 3.5–4.0 mm posterior to the limbus is recommended. In our research, however, a difference of 0.77 mm in mean CBL between the group with short AL and the group with long AL is demonstrated, implying that the mean CBL in very short and very long eyes differs significantly. These findings suggest that the AL should be taken into account for pars plana access and that it would be advisable to prefer the shorter or longer recommended distance (3.5 and 4.0 mm, respectively) from the limbus, which correlates with the AL. If AL is > 25 mm, a distance of 4.0 mm from the limbus should be chosen; and if AL is < 22.5 mm, a distance of 3.5 mm seems adequate.

Trial registration number and date

NCT00564291, 27 Nov 2007

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.