Image-guided navigation in posterior orbital tumour surgery: a comparative cohort study

ABSTRACT

Purpose

The posterior orbit is a confined space, harbouring neurovascular structures, frequently distorted by tumours. Image-guided navigation (IGN) has the potential to allow accurate localisation of these lesions and structures, reducing collateral damage whilst achieving surgical objectives.

Methods

We assessed the feasibility, effectiveness and safety of using an electromagnetic IGN for posterior orbital tumour surgery via a comparative cohort study. Outcomes from cases performed with IGN were compared with a retrospective cohort of similar cases performed without IGN, presenting a descriptive and statistical comparative analysis.

Results

Both groups were similar in mean age, gender and tumour characteristics. IGN set-up and registration were consistently achieved without significant workflow disruption. In the IGN group, fewer lateral orbitotomies (6.7% IGN, 46% non-IGN), and more transcutaneous lid and transconjunctival incisions (93% IGN, 53% non-IGN) were performed (p = .009). The surgical objective was achieved in 100% of IGN cases, with no need for revision surgery (vs 23% revision surgery in non-IGN, p = .005). There was no statistically significant difference in surgical complications.

Conclusion

The use of IGN was feasible and integrated into the orbital surgery workflow to achieve surgical objectives more consistently and allowed the use of minimal access approaches. Future multicentre comparative studies are needed to explore the potential of this technology further.

KEYWORDS:

• Orbital surgery
• orbit
• navigation
• image-guidance
• orbital tumours

Introduction

Orbital masses are challenging to treat due to the confined pyramid-shaped anatomy of the orbit, which contains tightly packed neurovascular structures and extraocular muscles, as well as their proximity to the anterior and middle cranial fossa.¹ Patients present with neuro-ophthalmic signs and symptoms due to direct pressure, damage or infiltration of orbital structures. This may result in optic nerve dysfunction, cranial nerve palsies, globe displacement, impaired ocular motility, and pupillary abnormalities. If untreated, these symptoms may become permanent and in extreme cases, the underlying diseases may be fatal.² Orbital tumours have to be approximately 1 cm in size before they cause any symptoms as the surrounding tissues expand to accommodate the slowly growing mass, potentially resulting in delayed diagnosis.^3–8 The displacement and infiltration of these tissues caused by space-occupying lesions, make the intraoperative identification of anatomical landmarks difficult, adding an extra layer of complexity to orbital surgery.^9,10

Half of orbital pathologies are neoplastic, and despite the majority being benign, they still require a biopsy for diagnostic purposes, and often require resection for symptom resolution. In adults above the age of 65, up to 58% of these lesions are malignant.^11–13 Therefore, surgical biopsy or resection is often necessary and intraoperative damage to the delicate intra-orbital structures and the globe itself, which can be as high as 12.4% in posterior orbital surgery, may lead to serious complications such as permanent vision loss, cranial nerve palsies and even cerebrospinal fluid leaks in some cases.^14,15

Currently, safe access to the posterior orbital space often necessitates orbitotomy with bone removal in order to access the space behind the eyeball. Lateral orbital bone removal, i.e. lateral orbitotomy, is often required to access space behind the eyeball and has been found to increase the risk of postoperative complications by 35%; these can range from injury to extraocular muscles, globe rupture, corneal anaesthesia, orbital haematoma and loss of vision.^16,17 The risk of blindness following orbital surgery is reported to be between 0.84% and 24% and it is more common with orbital apex tumours, with the highest incidence associated with vascular tumours.^14–17 This is reported to be due to direct nerve injury or ischemic damage to the optic nerve or retina, or due to central retinal artery occlusion secondary to excessive manipulation and bleeding in lateral orbitotomies.^14–17 One study, which included benign and malignant tumours, found the complication rate to be 12.4%, with the highest rates following lateral orbitotomy for posterior orbital and intraconal lesions.^14,15

When neurosurgeons were faced with similar challenges due to the complexity of the intracranial anatomy, they utilised a method known as stereotaxis. This is the principle behind modern image-guided systems, which use external reference markers to locate internal surgical landmarks by correlating a patient’s actual anatomy with preoperative scans through a navigation platform. In preoperative planning, this helps to assess the extent of the pathology and plan the safest approach, and intraoperatively it defines the change in position of normal structures, facilitating complete resection, and reducing collateral damage.^2,18–20 The anatomy of the orbit should lend to the benefits of similar technologies, but they have not yet been widely adopted by orbital surgeons.

In recent years, innovations such as endoscopy and CT navigation have been explored in orbital surgery to enhance procedural accuracy and minimize surgical damage.^21,22 Numerous studies have explored the use of IGN for a range of orbital pathologies.^21,23–35 However, these studies have been limited by small sample sizes and lack of a control group.^21,23–35 Previously studied versions of the technology required additional imaging and the use of head clamps (e.g. using optical IGN, instead of electromagnetic IGN) – limiting scalability and practicality in orbital surgery.^23,28 Therefore, we sought to perform a comparative study of state-of-the-art electromagnetic IGN in contemporary posterior orbital tumour surgery – exploring its feasibility, effectiveness and safety.

Materials and methods

Overview

We conducted a comparative cohort study involving the application of a surface-based head clamp-free electromagnetic (EM) IGN system in consecutive posterior orbital tumour surgeries, and we compared the outcomes with a similar retrospective cohort of orbital tumours resected without the use of IGN, to assess the feasibility, effectiveness and safety of IGN in orbital tumour surgery. The study was approved by our institutional review board (RV054/2022).

Primary outcomes

1. Feasibility was assessed by the recording of set-up time, and ability to attain accurate registration consistently.

2. Effectiveness was evaluated by the ability to achieve the surgical objective (maximum resection with margin clearance or to retrieve a diagnostic histologic specimen) with a single procedure (without the need for revision surgery), and whilst using minimal access surgical approaches.

3. Safety was evaluated by the occurrence of surgical complications.

Secondary outcomes

1. Visual outcomes on follow-up – including best correct visual acuity (BCVA) via logMAR (logarithm of minimal angle of resolution); colour vision, visual fields, and optical coherence tomography (OCT).

2. Other ocular outcomes on follow-up – including globe displacement, proptosis, lid position and extra-ocular movements.

IGN system set-up and feasibility assessment

We used the StealthStation^TM S8 (Medtronic, Dublin, Ireland) IGN system for this study, utilising its electromagnetic navigation system. This comprises a pillow-shaped flat emitter, which generates an electromagnetic field, a reference tracker (butterfly-shaped, attached to the patient’s forehead or temple), navigation probe which is used for registration and navigation. The system functions by creating a virtual 3D model of the patient’s imaging and then aligning this with the patient’s surface anatomy in a process called registration. The system localises the patient and registered model relative to the electromagnetic reference tracker. Therefore, the reference tracker must remain in the same location relative to the patient, otherwise the model and patient will become misaligned. As the reference tracker is connected to the patient’s forehead using an adhesive, when the patient’s head moves, the reference tracker moves with it as a single unit, and therefore a head clamp to keep the head still is not required for EM IGN. This is in contrast to optical IGN and older EM IGN systems where the reference tracker and patient are two separate units and therefore the head must be clamped so that the position relative to the reference tracker remains constant. After registration, intra-operative navigation occurs by tracking the electromagnetic navigation probe as it moves in relation to the reference tracker (and therefore the patient), which is mapped by the system to the pre-operative imaging in real time.

Figure 1 shows a simulated set-up at our centre, with the flat emitter placed under the standard gel ring, and the entire system therefore occupying little operative space. The field is prepped and draped in a standard fashion, and after satisfactory placement of the reference tracker, registration is completed. We used a surface-based registration, which can be done via either selecting static points around the orbits or via skin tracing. We used the skin tracing method of surface-based registration, which was more user-friendly and faster in our anecdotal experience. We trace the skin in a “sunglasses” pattern, over the bony anatomy of the orbital rim, extending medially across the glabella, and laterally along the zygomatic arch to the tragus. This method does not require additional fiducials (fixed reference markers in the form of electromagnetic skin stickers, which can be used for registration) to be placed pre-operatively during imaging.

Figure 1. StealthStation^TM S8 electromagnetic image-guided navigation system illustrative set-up. (A) represents the placement of the flat emitter under standard supportive headrests, with the display console at the head end. (B) displays the adhesive reference tracker on the patient’s forehead, and the use of the navigation pointer to complete surface-based registration. (C) demonstrates a side view of this low-profile ergonomic system.

Preoperative imaging used for registration and navigation comprised of CT orbits, acquired using a 64-slice CT Siemens Somatom, 0.625 m with contrast, and reconstructed in three planes with 1 mm slices. The field of view initially included the tip of the nose based on sinus navigation protocols, but feedback from progressive orbital navigation surgeries indicated that a field of view encompassing the supraorbital ridge and tragus was sufficient for effective navigation intraoperatively. Preoperative MRI orbits were performed on a Siemens Sola 1.5T MRI system, including coronal STIR, coronal T1 without fat saturation, coronal T1 with fat saturation, with and without contrast (3 mm slice thickness). Additionally, higher resolution coronal T2 weighted sequences were acquired (2 mm slice thickness) to aid navigation. These CT and MR images were fused using the Stealth console, before registration.

The system’s feasibility was assessed by measuring the time required to complete registration and to achieve a navigation accuracy of 1.2 mm or less. This intraoperative navigation accuracy was ascertained by placing the navigation pointer on defined visible anatomical landmarks of the orbit and comparing the actual position of the pointer to the computed pointer position displayed on the reference image (in axial, coronal, and sagittal radiological planes). The difference (if present) between the actual pointer position and computed pointer position was measured by sterile callipers. Landmarks used were the lateral canthus, medial canthus, and nasion, and once the lesion was exposed, its anterior surface.

IGN cohort – sampling and data collection

Included in this study were orbital tumour resections and biopsies from patients of all ages, carried out by a single consultant surgeon in a dedicated tertiary referral hospital for ophthalmology between October 2018 and December 2022. Tumours included were posterior to the globe (both intraconal and extraconal lesions). In each case, the surgical objective was either a) safe maximum resection and debulking or b) diagnostic biopsy. Excluded from the study were tumours located solely anterior to the globe and cases requiring a joint neurosurgical approach with craniotomy, as well as non-tumour orbital surgery.

Data collection included patient demographics (age, sex), tumour characteristics (tumour type, laterality), operative details (surgical goal, approach used and need for orbital bone removal) and post-operative outcomes (need for revision surgery, complications, and ophthalmic outcomes). In cases where the surgical goal was total resection, the completeness of excision was assessed based on the alleviation of neuro-ophthalmological symptoms, proptosis, globe displacement and radiologically via MRI.

In terms of ophthalmic outcomes, data collected pre-operatively and follow-up (at 12–24 months) included pre- and post-operative log MAR visual acuity, colour vision assessment (using Ishihara test plates) and kinetic and central static visual field assessment (Octopus perimeter). Extra-ocular motility was recorded and where required a Hess test was performed. Assessment of lid position and globe displacement (including proptosis, measured with Hertel’s exophthalmometer) was also recorded. A complete anterior (pupillary responses, intraocular pressure) and posterior segment examination followed. Finally, OCT (Zeiss) was also recorded assessing the integrity of ganglion and retinal nerve fibre layers.

Non-IGN control cohort – sampling and data collection

In this group, patient data from 2002 onwards was screened from medical charts or records of the Hospital Inpatient Enquiry (HIPE) reporting database, which is the official source used by the Department of Health in Ireland for collecting patient demographic, clinical and administrative data. The data was then coded by trained clinical coders using the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, Australian Modification (ICD-10-AM), Australian Classification of Health Interventions (ACHI), and Australian Coding Standards (ACS), 8th Edition. Multiple codes were used to ensure the comprehensive inclusion of female and male patients of all ages treated for orbital tumours. Following an identical inclusion and exclusion criteria to the contemporary cohort, only patients with posterior orbital tumours (posterior to the globe, extraconal and intraconal) were included. All historical control cases were performed by a different single senior orbital surgeon, in their final 15 years of practice. Retrospective collection of the same data points as the IGN cohort was performed. Owing to the historical nature of the dataset, OCT and Octopus visual field data were not consistently available. Visual acuity was assessed via Snellen chart rather than log MAR.

Data analysis

Statistical analyses were guided by a statistician and included the one-sample t-test and Pearson’s chi-square test for comparing baseline variables, and McNemar’s test with Edward’s correction and Wilcoxon Signed-Ranked test for comparing outcomes.

Results

Overview and baseline characteristics

In the IGN cohort, there were 30 patients with posterior orbital tumours operated on between October 2018 and August 2022, whilst in the historical cohort, 26 patients were identified from 2000 to 2015. The two groups were similar (Table 1), and the only statistically significant difference was mean age – with the IGN group having a higher mean age (47 years, vs 34 years in non-IGN cohort, p = .02). The two cohorts were not significantly different in gender (p = .57), laterality (p = .47), prevalence of benign (p = .11) and malignant tumours (p = .62).

Table 1. Baseline characteristics and statistical comparison between the two cohorts. Percentages for each variable are reported with the total number of cases in the respective cohort as the denominator. *Statistical comparison was performed using Pearson’s chi-square test of independence for all variables except for comparing mean age (where a one-sample t-test was used).

	Control cohort without IGN (n = 26)	IGN cohort (n = 30)	*p value
Demographics
Mean Age (range)	34 years (4–70)	47 years (4–81)	.016
Female : Male	11:15	15:15	.565
Tumour Laterality
Right	12 (46.2%)	11 (36.7%)	.472
Left	14 (53.8%)	19 (63.3%)	.472
Benign Tumours	13 (50.0%)	16 (53.3%)	.111
Intraconal:extraconal	5:8	7:9
Arteriovenous malformations	1 (3.8%)	3 (10.0%)	.373
Intraconal:extraconal	1:0	2:1
Cavernous malformations	3 (11.5%)	3 (10.0%)	.849
Intraconal:extraconal	2:1	3:0
Dermoid cysts	3 (11.5%)	0 (0.0%)	.560
Intraconal:extraconal	0:3	0:0
Idiopathic orbital inflammatory disease	1 (3.8%)	4 (13.3%)	.215
Intraconal:extraconal	0:1	2:2
Schwannomas	3 (11.5%)	1 (3.3%)	.234
Intraconal:extraconal	2:1	0:1
Meningiomas	1 (3.8%)	0 (0.0%)	.280
Intraconal:extraconal	0:1	0:0
Encephaloceles	1 (3.8%)	0 (0.0%)	.280
Intraconal:extraconal	0:1	0:0
Granulomatosis with polyangiitis	0 (0%)	2 (6.7%)	.180
Intraconal:extraconal	0:0	0:2
IgG4 disease	0 (0%)	2 (6.7%)	.180
Intraconal:extraconal	0:0	0:2
Solitary fibrous tumours	0 (0%)	1 (3.3%)	.347
Intraconal:extraconal	0:0	0:1
Malignant Tumours	13 (50%)	14 (46.7%)	.615
Intraconal:extraconal	3:10	6:8
Lymphoproliferative tumours	6 (23.1%)	6 (20.0%)	.779
Intraconal:extraconal	1:5	2:4
Rhabdomyosarcoma	3 (11.5%)	2 (6.7%)	.522
Intraconal:extraconal	1:2	1:1
Metastatic	2 (7.7%)	3 (10.0%)	.764
Intraconal:extraconal	0:2	1:2
Astrocytoma	1 (3.8%)	0 (0.0%)	.280
Intraconal:extraconal	1:0	0:0
Adenoid cystic carcinoma	1 (3.8%)	0 (0.0%)	.280
Intraconal:extraconal	0:1	0:0
Glioma	0 (0%)	1 (3.3%)	.347
Intraconal:extraconal	0:0	1:0
Neuroblastoma	0 (0%)	1 (3.3%)	.347
Intraconal:extraconal	0:0	1:0
Myofibroblastic tumour	0 (0%)	1 (3.3%)	.347
Intraconal:extraconal	0:0	0:1

Primary outcomes

In terms of feasibility, registration accuracy of <1.2 mm was consistently achieved in every IGN case. Time to achieve this registration accuracy was progressively reduced, particularly after five cases, reflecting a short learning curve (Figure 2). In each case, verification of navigational accuracy using intra-operative landmarks revealed precise localisation of structures with no macroscopic error. This was maintained throughout all cases, and therefore no intra-operative re-registration or calibration was required in our case series. We did, however, experience interference during navigation from nearby mobile phones (within approximately a metre radius) but not from our standard stainless steel surgical instruments.

Figure 2. Line chart of time to accurate registration over consecutive cases.

In terms of effectiveness, there was a significant reduction in the use of lateral orbitotomy in the IGN group (p = .001), with comparatively higher use of more minimal non-bony access approaches like transconjunctival, transcutaneous lid crease, medial Lynch and vertical medial 1/3^rd and lateral 2/3^rd incision (Table 2). The surgical objective in IGN cases was resection in 18 cases (18/30, 60%) and diagnostic biopsy in 12 cases (12/30, 40%). This was achieved in all 30 IGN cases, with no revision surgeries during follow-up. In the non-IGN group, the surgical goal was resection in 12 cases (12/26, 46.1%) and diagnostic biopsy in 14 cases (14/31, 53.8%). In this cohort, six cases (three biopsy and three resection cases) required revision surgery due to failure of the surgical goal. Therefore, the surgical goal was achieved more consistently in the IGN cohort (p = .005).

Table 2. Primary outcomes and statistical comparison between the two cohorts. *Statistical comparison was performed using Pearson’s chi-square test of independence for all variables.

Variables	Control cohort without IGN (n = 26)	IGN cohort (n = 30)	*p value
Surgical approach			.009
Lateral orbitotomy	12 (46.2%)	2 (6.7%)	.001
Transconjunctival	4 (15.4%)	6 (20.0%)	.653
Transcutaneous lid crease	10 (38.5%)	18 (60.0%)	.107
Medial Lynch	0 (0.0%)	3 (10.0%)	.097
Vertical (medial or lateral) incision	0 (0.0%)	1 (3.3%)	.347
Need for Reoperation			.005
Single attempt	20 (76.9%)	30 (100.0%)	.005
Second attempt	6 (23.1%)	0 (0.0%)	.005
Other surgical complications			.302
New visual deficit	1 (3.8%)	0 (0.0%)	.280
Diplopia requiring strabismus surgery	1 (3.8%)	0 (0.0%)	.280
No complications	24 (92.3%)	30 (100.0%)	.121

From a safety perspective, in the non-IGN group, one patient suffered permanent total visual loss post-operatively. This was after the excision of an orbital apex cavernous haemangioma via lateral orbitotomy, with the visual loss attributed to central retinal artery occlusion secondary to excessive manipulation and bleeding, causing intraoperative vasospasm. Additionally, one patient suffered from postoperative strabismus requiring surgery in the non-IGN group (Table 2). In the IGN group, none of the patients had any visual deficit nor any other surgical complications postoperatively; however, these differences were not statistically significant (postoperative visual deficits p = .280; complications p = .302).

Secondary outcomes

Upon follow-up of the IGN group, there was a statistically significant improvement in visual fields, colour vision and OCT GNFL when comparing the preoperative measurements with the postoperative outcomes (Table 3). There was a significant reduction in globe displacement from a median of 3 mm (interquartile range [IQR] 2–4 mm) pre-op to a median of 1 mm (IQR 1–2 mm) post-op (p < .001 via Wilcoxon Signed-Ranked test; z −4.015). Furthermore, there was a statistically significant reduction in the extent of proptosis (median 2 mm, IQR 1–3 mm; p < .001 via Wilcoxon Signed-Ranked test; z −4.217).

Table 3. Visual outcomes in the IGN cohort, pre- and post-operatively. Statistical analysis was performed via McNemar’s test, with Edward’s correction.

Outcome	Pre-operative deficit	Post-operative deficit	% Improved	p Value
BCVA	18	15	16.7% (3/18)	.700
Visual field	7	2	71.4% (5/7)	<.001
Colour vision	6	2	66.7% (4/6)	<.001
OCT GNFL	10	2	80% (8/10)	<.001
Extra-ocular movements	17	13	23.5% (4/17)	.844
Lid position	16	6	62.5% (10/16)	.034

These outcomes reflected a wide variety of pathology and surgical goals with subgroups too small for meaningful stratified analysis. There was a high proportion of missing data and data recorded using older measurement techniques in the historic control (non-IGN) cohort group, and therefore they are not reported.

Discussion

Principal findings

In this comparative study, we have demonstrated the feasibility of integrating EM IGN technology into a contemporary orbital tumour surgery workflow. This has allowed us to achieve surgical objectives more consistently, using less invasive approaches, without an increase in surgical complications.

Comparing the IGN intervention group with a similar historical cohort, the former group showed more transcutaneous incisions without the need for orbital bone removal, demonstrated by the statistically significant reduction in lateral orbitotomies. We attribute this difference to the assistance of precise lesion localisation using navigation, obviating the need for larger incisions with bone removal. The use of more extensive approaches such as lateral orbitotomies not only increases operative time but has also been associated with a higher complication profile due to a higher risk of collateral damage to surrounding tissues.¹⁵ Despite the use of more minimal access approaches in the IGN cohort, the surgical objective (whether it was biopsy or total resection) was consistently achieved, and again our anecdotal experience is that this is due to the improved lesion localisation offered by navigation assistance. Several studies have shown that the benefits of image-guided navigation include improved anatomical localisation and thus procedure success and operative time (potentially translating into beneficial outcomes). The benefits of this include avoiding unnecessary exploration and dissection (avoids collateral damage to surrounding structures), and expedited access/localising to the index pathology – resulting in decreased operating time and minimally invasive procedures.^18,33,36 Furthermore, repeat surgery either for incomplete excision, negative biopsy or recurrence was reported in 23% of the non-IGN cases, with these revision surgeries associated with a further increased risk of complications.^14,15 This further contextualises the potential benefits to be gained from using technological adjuncts such as IGN.

For any surgical innovation, its potential benefits must be balanced against its feasibility and potential risks. Using a modern EM IGN system (Stealth S8, Medtronic), we were able to achieve an ergonomic setup which did not interfere with positioning or surgical access. This is unlike previous studies, which used systems requiring Mayfield head clamps, pre-operative fiducials and other large pieces of equipment.^23,33,36 There was a short learning curve to learning the set-up and registering the patient to their pre-operative images, and otherwise, there were minimal deviations from our centre’s standard of care protocols. After five cases, our set-up time was less than 5 minutes. We did not experience any issues with navigational accuracy after successful registration.^28,37 However, in general, there are inherent limits to the navigation provided by IGN systems based on pre-operative imaging alone, as they are not sensitive to major intra-operative tissue shifts.²⁰

Findings in the context of the literature

In surgical practice, across all disciplines, the overarching aim is to continuously improve the surgical outcomes of our patients. Technological innovation is a frequent medium for this improvement, but these must be carefully and systemically evaluated for their safety and feasibility, prior to widespread adoption. Orbital surgery presents unique challenges anatomically due to the abundance of intricate anatomy and delicate structures in a tight space, and this is particularly challenging when dealing with the posterior aspect of the orbit. Traditionally, accessing these challenging areas has necessitated extensive incisions and the removal of orbital bone. Therefore, it becomes imperative to explore techniques that can render such surgeries more precise – to allow localization of lesions and protection of surrounding structures from collateral damage.

Computer-assisted navigational surgery has been accessible for nearly two decades and has undergone progressive development. It was pioneered in neuro-oncological surgery – to enhance precision in surgical planning, tumour localization, and post-resection margin assessment – and is now the gold standard across neurosurgical subspecialties. It has also become an integral part of the pre- and intra-operative setup in some otorhinolaryngology centres for endoscopic sinus surgery and skull-based procedures.^2,19,38–41

In the current literature, the majority of studies assessing the application of IGN in orbital tumour surgery are small non-comparative case series.^{22,24,27,32,36} Our findings are in line with many of these studies, which generally suggest that image-guided techniques are feasible, accurate and may improve outcomes compared with traditional techniques.^23,29,30,35 For example, Karcioglu et al. demonstrated the benefit of IGN in three cases of orbital tumour resection.²⁷ They reported that the interactive nature of image guidance was useful in orbital surgery to orient the surgeon to the exact location within the surgical field and to determine the tumour margins. Enchev et al. had successful surgical outcomes in four cases of orbital tumour removal undertaken with the help of navigation.¹⁸ Furthermore, Terpolilli et al. also looked at 23 cases of skull-based tumours with orbital involvement and found that intraoperative navigation allowed control of resection in cases of uncertainty and can help to improve the extent of maximal safe resection, especially in the case of osseous tumour parts and masses within the orbit.²² Similarly, Campbell et al. documented the use of CT navigation in orbital apex lesions where the approach was multidisciplinary and consisted of an orbital surgeon, neurosurgeon and ENT surgeon combined.²¹ In a later study, Campbell et al. used optical IGN requiring bony fiducials in 23 orbital tumour (anterior and posterior) cases, noting its utility in bony orbitotomy planning and anatomical structure recognition.²³ Finally, many of these studies used navigation systems which required fiducials and head clamps (e.g. optical navigation) or were older generations – unlike the newer, electromagnetic (head clamp free), system which does not require pre-operative fiducials and has integrated seamlessly into our orbital surgery practice.^23,27,32,36

Finally, the surgeon’s perspective is crucial in the adoption of new technology. Hussain et al. undertook a study which involved sending a questionnaire to surgeons regarding the feasibility and user experience with image-guided navigation. It was observed that the majority of orbital surgeons had superficial or no experience with computer-assisted surgery. The proportion of IGN-assisted orbital surgery performed in practice was significantly associated with the surgeon’s experience with the technique, and this response was varied and was based on the cost and availability of the technology.⁴² This confirmed an expected variation in the perception and use of navigation in orbital surgery, but they did demonstrate that patient benefit and integration of refined and cost-effective systems into operating room environments might influence its future role.⁴²

Strengths and limitations

The strengths of this study are its use of a state-of-the-art and ergonomic IGN system, integrated into a varied tertiary orbital surgery environment, with a comparative assessment. Therefore, to our knowledge, this is the first study of its kind. There are, however, numerous limitations to this study, including the moderate sample size and single-centre nature. The retrospective control cohort was retrospectively sampled, resulting in difficulties in attaining a complete visual outcome dataset per case, compounded by the difference in measurement instruments used during that period (e.g. lack of logMAR, and routine OCT). However, surgical data (objectives, outcomes, and complications) were consistently available. The comparatively lower volume of the retrospective control cohort may be explained by the limitations of retrospective sampling in a largely paper-based healthcare system, as well as a genuinely lower volume of posterior orbital surgery tumours. The latter is explained by increased detection of posterior orbital tumours in the present day due to increased imaging availability, and the increased consolidation of orbital tumour services into specialised centres in more recent years. Furthermore, although both cohorts had different lead surgeons, they were at a similar level of experience. There have ,of course, been numerous other changes in wider healthcare delivery and medical technology availability between these periods which are difficult to quantify. Future studies should therefore perform prospective comparative analysis, in a multicentre fashion, and eventually via a randomised controlled trial (e.g. cluster RCT) to assess the generalisability and reproducibility of our results, further explore the benefits of this technology, and assess its cost-effectiveness.

Conclusions

The orbit is a densely packed and complex anatomical space. Posterior orbital tumours may distort the structures within and are compounded by small and narrow surgical corridors; this makes the surgical management of these tumours challenging. In other fields facing similar challenges, for example, neurosurgery and otolaryngology, image-guided surgery has been adopted to assist with safe surgical access, whilst minimising collateral damage. This is particularly important in orbital tumour surgery, where a large proportion of these tumours may be malignant, and the surrounding neurovascular structures are responsible for critical functions (e.g. vision). In this single-centre comparative study of the use of IGN in contemporary posterior orbital surgery, we found its integration was feasible and offered significant benefits in more consistent surgical objective success and more minimal access approaches. We attribute this to the improved lesion localisation it offered. Future studies should be multicentre, and build into randomised comparative studies to further explore the potential benefits of this technology across healthcare contexts, and its cost-effectiveness.

Acknowledgements

The StealthStation^TM S8 Electromagnetic image-guided navigation system used in this study was loaned by Medtronic to the Royal Victoria Eye and Ear Hospital.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.