Shape analysis of rectus extraocular muscles with age and axial length using anterior segment optical coherence tomography

Abstract

Purpose This study aimed to evaluate the shape of the extraocular muscles (EOMs) in normal subjects using the en-face images of anterior segment optical coherence tomography (AS-OCT). The EOM insertion and the direction of the muscle fibers were investigated. Subjects and methods A total of 97 healthy normal subjects (194 eyes) at Okayama University Hospital (age, 47.1±21.5 years; range, 8–79 years) participated in the study. A series of 256 tomographic images of the rectus EOMs were captured using the C-scan function of the AS-OCT (CASIA2, TOMEY Co., Japan), and the images were converted to en-face images in multi-TIFF format. The anterior chamber angle to EOM insertion distance (AID) and the angle of the muscle fibers from the insertion site (angle of muscles) were measured from the images. The correlations of AID and angle of muscles with age and axial length were investigated and evaluated. Results AID and angle of muscles were significantly correlated with age or axial length in some EOMs. The AIDs of medial rectus (MR) (P = 0.000) and superior rectus (SR) (P = 0.005) shortened with age. The AIDs of MR (P = 0.001) and inferior rectus (IR) (P = 0.035) elongated with axial length, whereas lateral rectus (LR) (P = 0.013) shortened. The angles of MR (P = 0.001) and LR (P = 0.000) were found to have a more downward direction toward the posterior in older subjects. Conclusion En-face images can be created by AS-OCT, and the shape of the EOMs in normal subjects using these image measurements was available. With the ability to assess the EOMs, AID and angle of muscles are expected give useful information for treating and diagnosing strabismus-related diseases.

Do rectus muscle parameters vary between emmetropes and myopes?

“…[19][20][21][22][23][24][25][26][27][28] The paucity in the literature in exploring the association of medial (MR) and lateral rectus (LR) muscle parameters with varying degrees of myopia warrants investigation to understand this relationship, especially considering that the biomechanical properties of the eye, similar to structural properties, may also differ between emmetropes and myopes. 24,25,27,29,30 With this background on the significant role of EOMs during convergence, and in turn the association of prolonged nearwork with myopia, it is of interest to explore whether the EOM parameters show any association with myopia akin to thinning/atrophy of various ocular structures with ocular stretching. We aimed to examine the thickness, area and insertion site of the horizontal recti muscles in individuals with emmetropia and different degrees of myopia using a high-resolution, swept-source, optical coherence tomography (SS-OCT).…”

“…While previous studies investigated EOM parameters (especially muscle insertion distance and thickness) using instruments such as Vernier callipers, ultrasound B‐scan, magnetic resonance imaging and optical coherence tomography (OCT), these either estimated the distances in cadaveric eyes or did not involve humans with varying degrees of myopia 19–28 . The paucity in the literature in exploring the association of medial (MR) and lateral rectus (LR) muscle parameters with varying degrees of myopia warrants investigation to understand this relationship, especially considering that the biomechanical properties of the eye, similar to structural properties, may also differ between emmetropes and myopes 24, 25,27,29,30 …”

Clinical Role of Swept Source Anterior Segment Optical Coherence Tomography in Strabismus Re-Operation with Lost Surgical Details

“…Nevertheless, we feel that futuristic concepts such as shape analysis of extra ocular muscle can benefit our understandings immensely in identifying operated muscle details as compared to current cross-sectional imaging techniques. 13 …”

Defining the Clinical Role of Swept-Source Anterior Segment Optical Coherence Tomography in Eyes Undergoing Strabismus Surgery

“…In fact, in some cases, the muscle presence and its rough estimations were more important than the perfect readings. 4) As the current technology is only limited to cross-sectional imaging, the actual enface mappings 14 were genuinely lacking in our study.…”