Measurement of orbital volume after enucleation and orbital implantation

Role of Structural, Metabolic, and Functional MRI in Monitoring Visual System Impairment and Recovery

The visual system, consisting of the eyes and the visual pathways of the brain, receives and interprets light from the environment so that we can perceive the world around us. A wide variety of disorders can affect human vision, ranging from ocular to neurologic to systemic in nature. While other noninvasive imaging techniques such as optical coherence tomography and ultrasound can image particular sections of the visual system, magnetic resonance imaging (MRI) offers high resolution without depth limitations. MRI also gives superior soft-tissue contrast throughout the entire pathway compared to computed tomography. By leveraging different imaging sequences, MRI is uniquely capable of unveiling the intricate processes of ocular anatomy, tissue physiology, and neurological function in the human visual system from the microscopic to macroscopic levels. In this review we discuss how structural, metabolic, and functional MRI can be used in the clinical assessment of normal and pathologic states in the anatomic structures of the visual system, including the eyes, optic nerves, optic chiasm, optic tracts, visual brain nuclei, optic radiations, and visual cortical areas. We detail a selection of recent clinical applications of MRI at each position along the visual pathways, including the evaluation of pathology, plasticity, and the potential for restoration, as well as its limitations and key areas of ongoing exploration. Our discussion of the current and future developments in MR ocular and neuroimaging highlights its potential impact on our ability to understand visual function in new detail and to improve our protection and treatment of anatomic structures that are integral to this fundamental sensory system. LEVEL OF EVIDENCE 3:   TECHNICAL EFFICACY STAGE 3:  .

Amplitude of movements with conical or spherical implants in anophthalmic socket

PURPOSE

To evaluate the amplitude of movement in anophthalmic sockets reconstructed with conical or spherical orbital implants with and without an external ocular prosthesis (EOP), and whether the fornix depth could play a role.

METHODS

Prospective observational study involving unilateral anophthalmic sockets evaluated the amplitude of movement with conical (20 subjects) or spherical (16) non-porous orbital implants, with and without an EOP, having the contralateral eye as the control group. Standardized photographs were obtained in the four gaze directions and measurements were performed using the Image J software. The upper and lower fornix depths were measured using rulers.

RESULTS

Compared to the contralateral eye, the median movement amplitude without EOP was smaller with conical implants in supraduction (-0.88 mm, p=0.008), abduction (-2.26 mm, p<0.001) and adduction (-0.91 mm, p=0.008). Spherical implants had reduced movement only in abduction (-2.63 mm, p<0.001). Conical and spherical implants had similar amplitudes of movement in all versions, and were always smaller compared to the control. The median movement amplitude with the EOP was -3.05 mm (p=0.001) than without the EOP in abduction and -2.07 mm (p=0.020) in adduction, regardless of implant format. The fornix depth did not affect the orbital implants or EOP movement amplitude's median.

CONCLUSION

Conical and spherical implants provide similar amplitude of movement and fornix depth did not have an influence on it. The amplitude of movement was significantly limited compared to the contralateral eye and was even more reduced if the EOP was in place with conical or spherical implant formats.

Conical Biosilicate Implant for Volume Augmentation in Anophthalmic Sockets

The ideal implant for anophthalmic socket reconstruction has yet to be developed. Biosilicate, a highly bioactive glass-ceramic, has been used in the composition of conical implants, which were initially tested in rabbit orbits with excellent results. However, the use of this material and the conical shape of the implants require further study in the human anophthalmic socket. Thus, we propose the use of a new conical implant composed of Biosilicate for orbital volume augmentation in anophthalmic sockets. This prospective, randomized study included 45 patients receiving conical implants composed of either Biosilicate or polymethylmethacrylate (control). Patients were evaluated clinically before and 7, 30, 60, 120, and 180 days after implantation. Systemic evaluations, laboratory tests, and computed tomography of the orbits were performed preoperatively and 180 days postoperatively. Both groups had good outcomes with no significant infectious or inflammatory processes. Only 1 patient, in the Biosilicate group, had early implant extrusion. Laboratory tests were normal in both groups. Computed tomography scans showed that the implants in both groups were well positioned. The new conical implant composed of Biosilicate was successfully used for anophthalmic socket reconstruction. This implant may provide a good alternative to the only conical implant currently available on the market, which is composed of porous polyethylene.

Reliability of orbital volume measurements based on computed tomography segmentation: Validation of different algorithms in orbital trauma patients

PURPOSE

To compare the most common methods of segmentation for evaluation of the bony orbit in orbital trauma patients.

MATERIALS AND METHODS

Computed tomography scans (before and after treatment) from 15 patients with unilateral blowout fractures and who underwent orbital reconstructions were randomly selected for this study. Orbital volume measurements, volume difference measurements, prolapsed soft tissue volumes, and bony defect areas were made using manual, semi-automated, and automated segmentation methods.

RESULTS

Volume difference values between intact and damaged orbits after surgery using the manual mode were 0.5 ± 0.3 cm³, 0.5 ± 0.4 cm³ applying semi-automated method, and 0.76 ± 0.5 cm³, determined by automated segmentation (р = 0.216); the mean volumes (MVs) for prolapsed tissues were 3.0 ± 1.9 cm³, 3.0 ± 2.3 cm³, and 2.8 ± 3.9 cm³ (p = 0.152); and orbital wall defect areas were 4.7 ± 2.8 cm², 4.75 ± 3.1 cm², and 4.9 ± 3.3 cm² (p = 0.674), respectively.

CONCLUSIONS

The analyzed segmentation methods had the same accuracy in evaluation of volume differences between two orbits of the same patient, defect areas, and prolapsed soft tissue volumes but not in absolute values of the orbital volume due to the existing diversity in determination of anterior closing. The automated method is recommended for common clinical cases, as it is less time-consuming with high precision and reproducibility.

Radiological evaluation of sphenozygomatic suture fixation for restoration of orbital volume: A retrospective study

PURPOSE

Lateral displacement of fracture zygomaticomaxillary complex (ZMC) can cause significant increase in orbital volume leading to enophthalmos. The aim of this study was to radiologically evaluate the efficacy of sphenozygomatic (SZ) suture fixation for restoration of orbital volume after elevation of the temporalis in cases of fracture ZMC where the fixation of zygomatic arch (ZA) was deemed necessary through latero-posterior approach.

MATERIALS & METHODS

43 operated cases of fracture ZMC using 4-point fixation were divided into two groups. Group I (n = 24) cases had undergone reduction and fixation of SZ suture as fourth point of fixation by elevating temporalis muscle using hemicoronal approach. Group II (n = 19) cases had undergone reduction and fixation of Infraorbital (IO) rim as fourth point of fixation using preseptal transconjunctival approach. Both the groups were analyzed separately and compared for restoring the increased orbital volume on CT.

RESULTS

Difference in the pre-surgical orbital volume of both the groups was found to be statistically insignificant [p = .678]. In group I, the average bony orbital volume significantly reduced by 3.6 cc from 25.5 cc to 21.9 cc [p = .000] post-surgically. In group II, the average bony orbital volume reduced by 1.5 cc from 25.6 cc to 24.1 cc post-surgically There was a significant difference in the reduction of the increased orbital volume among the 2 groups (Group I: 3.6 cc, group II: 1.5 cc). The amount of reduction was more and statistically significant [p = .000] in the group I than group II.

CONCLUSION

SZ suture fixation is reliable in reducing fractures ZMC and restoring the increased orbital volume where the fixation of zygomatic arch (ZA) was deemed necessary through latero-posterior approach.

Three-Dimensional Cephalometric Analysis of Orbital Morphology Modification for Midface Correction Surgery

OBJECTIVES

The aim of this study was to create an evidence-based three-dimensional cephalometric analysis of orbits in order to perform time-efficient measurements of postoperative orbital morphology changes.

MATERIALS AND METHODS

The authors used 23 (11 bilateral and 1 unilateral) anatomical landmarks. Based on these, 6 planes, 12 angular and 16 linear measurements were determined. A three dimensional analysis was performed twice by two observers on pre and post-operative computed tomography scans of six patients who had undergone midface advancement. The mean, minimal and maximal difference, as well as standard deviation (SD) and intraclass correlation coefficient (ICC) for the inter- and intra-observer landmark selection reliability were calculated. Additionally, the mean, minimal, maximal difference and standard deviation between pre- and post-operative angular and linear measurements were calculated to examine a connection between the established measurements and any morphological change.

RESULTS

The inter and intra-examiner accuracy of all landmarks for three axes was >0.9 ICC. Despite excellent inter and intra-examiner agreement (<2.49 mm ± 2.05 mm SD) for the landmark selection, linear and angular measurements showed a mismatch, the mean SD for angular measurements was found to be 8.2° and the linear 3.04 mm.

DISCUSSION

The possible causes of linear and angular measurement discrepancies are discussed and the future direction for the development of three-dimensional cephalometric analysis of orbits proposed.

3D-assisted quantitative assessment of orbital volume using an open-source software platform in a Taiwanese population

Orbital volume evaluation is an important part of pre-operative assessments in orbital trauma and congenital deformity patients. The availability of the affordable, open-source software, OsiriX, as a tool for preoperative planning increased the popularity of radiological assessments by the surgeon. A volume calculation method based on 3D volume rendering-assisted region-of-interest computation was used to determine the normal orbital volume in Taiwanese patients after reorientation to the Frankfurt plane. Method one utilized 3D points for intuitive orbital rim outlining. The mean normal orbital volume for left and right orbits was 24.3±1.51 ml and 24.7±1.17 ml in male and 21.0±1.21 ml and 21.1±1.30 ml in female subjects. Another method (method two) based on the bilateral orbital lateral rim was also used to calculate orbital volume and compared with method one. The mean normal orbital volume for left and right orbits was 19.0±1.68 ml and 19.1±1.45 ml in male and 16.0±1.01 ml and 16.1±0.92 ml in female subjects. The inter-rater reliability and intra-rater measurement accuracy between users for both methods was found to be acceptable for orbital volume calculations. 3D-assisted quantification of orbital volume is a feasible technique for orbital volume assessment. The normal orbital volume can be used as controls in cases of unilateral orbital reconstruction with a mean size discrepancy of less than 3.1±2.03% in females and 2.7±1.32% in males. The OsiriX software can be used reliably by the individual surgeon as a comprehensive preoperative planning and imaging tool for orbital volume measurement and computed tomography reorientation.

Measurements of Orbital Volume using Cone-Beam Computed Tomography in Eye Movement Abnormalities

Purpose

To measure the orbital volume in adult patients with unilateral eye movement abnormalities originating in childhood.

Methods

Cone-beam computed tomography was performed in 2 patients with eye movement abnormalities. A 28-year-old woman was treated because of right divergent squint originating at 8 years of age after penetrating corneal trauma. A 38-year-old man was examined because of abnormal head posture caused by left superior oblique underaction originating at 6 years of age. Orbital scans were analyzed with Cranioviewer 3D craniofacial cephalometric program. We measured bony orbital area in 6 slices (in ventro-dorsal direction per 4.8 mm) in every orbit on coronal scans.

Results

The volume was more in the orbit with unilateral divergent squint and less in the orbit with unilateral superior oblique underaction compared to the contralateral orbital volume measurements.

Conclusions

Cranioviewer 3D craniofacial cephalometric program is suitable for volumetric analysis of the bony orbit on cone-beam computed tomography files. The development of the orbit can be influenced by extraocular muscle movements.