Identification and biometry of horizontal extraocular muscle tendons using optical coherence tomography.

PURPOSE: To purpose if this study was to determine whether the horizontal rectus muscle tendons (HRMTs) can be observed using anterior segment optical coherence tomography (AS-OCT) and to determine the repeatability of its measurements. Also, this study aimed to observe and measure the different external ocular structures at the level of the horizontal rectus muscle (HRM) insertion. METHODS: This was a retrospective, observational, descriptive and comparative study. Images were obtained utilizing the RTVue 100 CAM system. Eyes were analyzed at the three and nine o'clock position. Scans were performed for three different locations: the limbus, the ciliary body and the equator. All scans were analyzed by two graders, separately and blinded. Measurements were performed for: HRMT length; HRM thickness; conjunctival epithelium thickness; conjunctiva and Tenon's capsule thickness; scleral thickness; and external ocular thickness. RESULTS: Results were obtained from twenty eyes of ten volunteers. The conjunctival epithelium thickness was 52.33 µm, the total conjunctiva/Tenon's capsule thickness was 313.54 µm, the medial rectus (MR) thickness was 136.63 µm and the lateral rectus (LR) thickness was 181.65 µm. The MR tendon length was 1,426.88 µm, the LR tendon length was 1,433.65 µm, the scleral thickness was 489.91 µm and the total external ocular structure thickness was 785.17 µm. Intra-observer reproducibility (intraclass correlation coefficient [ICC]) for tendon length was 0.993 for grader #1, 0.989 for grader #2; the muscle thickness ICC was 0.990 for grader #1 and 0.981 for grader #2. The inter-observer reproducibility ICC for tendon length was 0.557; the ICC for muscle thickness was 0.834. CONCLUSIONS: It is possible to visualize and measure HRMTs using AS-OCT. Measurements of the HRM, as well as the surrounding external ocular tissues, can be achieved.

Anterior segment optical coherence tomography for imaging the sub-Tenon space.

In this study, we report the ability of anterior segment optical coherence tomography (AS OCT) in imaging the sub-Tenon space and its clinical application. High-speed AS OCT (Carl Zeiss Meditec, Dublin, Calif., USA) was used to visualize the sub-Tenon space during sub-Tenon injection. The sub-Tenon spaces, Tenon thickness, conjunctiva-Tenon thickness, injecting cannula position in relation to the sub-Tenon space and drug localization/distribution in the sub-Tenon space were analyzed. The sub-Tenon spaces of 12 of 11 patients were visualized with OCT during sub-Tenon injection up to 10-13 mm from the limbus. The mean conjunctiva-Tenon and Tenon thickness were 0.38 ± 0.08 and 0.21 ± 0.07 mm, respectively. The drug was tracked as bright white fluid. There was no conjunctival chemosis, subconjunctival drug or scleral perforation. Anterior segment OCT can be used for imaging the sub-Tenon space, especially during depot injections for confirmation of drug localization.

Anatomy of Tenons capsule.

BACKGROUND: The microscopic and macroscopic anatomy of the anterior and posterior Tenons capsule is described. METHODS: An observational anatomic study of twelve orbits of 6 cadavers (mean age 79.5 years) were examined microscopically and 8 orbits of 4 cadavers (mean age 76.8 years) were examined macroscopically. After orbital exenteration, an X-shaped incision was made in the specimens to include the posterior part of the globe. The sections were divided into four parts: superomedial; inferomedial; superolateral; and inferolateral. In the macroscopically examined specimens, the eyelids and globes were removed from the exenterated tissues and the appearance of Tenons capsule was studied. RESULTS: In the microscopic study, Tenons capsule covered the sclera beneath the conjunctiva and contained smooth muscle fibres in the anterior area. This anterior fascia, which had a thick appearance, reached the globe equator. From there, the capsule of the orbital fat, which contained no smooth muscle fibres, enveloped the sclera and reached the optic nerve. This was defined as the posterior capsule. In the macroscopic specimens, Tenons capsule had a thick and fibrous white appearance in the anterior area. More posteriorly, the capsule was thinner and more translucent. This thin capsular part was generally larger in the lateral area than in the medial area. CONCLUSIONS: Tenons capsule is composed of an anterior thick fibrous tissue comprising the orbital smooth muscle network and the posterior thin fibrous capsule of the orbital fat.