Traction Force Mapping of Tractional Retinal Detachments with Optical Coherence Tomography

Background: The aim of this study is to better understand the mechanical response of the retina to the tractional forces that result in a tractional retinal detachment (TRD) by creating a traction force map using a computational model. Study Design: A three-dimensional computational model of the retinal-subretinal segment was constructed based on anatomic knowledge and optical coherence tomography (OCT). The traction force map was represented in terms of von Mises stress distribution. Internal review board approval was obtained. Medical records were reviewed by one investigator to limit patient information exposure. Only deidentified OCT images were used in analysis. Results: Peak stress occurred in the detached retinal layer with the greatest curvature. The highest change in stress occurred at the margin of detachment. Conclusions: Traction force mapping can be used to quantify the stress occurring in the detached retina. This may be used to improve surgical approach.

of these competing forces is a tractional retinal detachment (TRD) and is, ultimately, a consequence of uncontrolled diabetes mellitus.
TRDs can involve the macula or involve only the periphery. There are multiple different grading systems for TRDs, including the Kroll et al. and Zarbin et al. grading systems [1]. Most surgeons will perform surgery when the TRD involves the macula or is highly likely to progress and cause damage to the macula.
The current preoperative workup can include many modalities of imaging and examination: intra-venous fluorescein angiography (IVFA), optical coherence tomography (OCT), B scan ultrasound, and a detailed binocular dilated examination with an indirect ophthalmoscope [1]. Examination with indirect ophthalmoscope gives the surgeon valuable preoperative data in relation to margins and height of the TRD. However, the view of the TRD can be obscured by vitreous hemorrhage and this makes ophthalmoscopy difficult to impossible.
Release of TRD membranes can have many complications that can be time consuming for the surgeon and be detrimental to the patient's visual outcome. Vitrectomy was required for the treatment of diabetic retinopathy in 5.6% of the patients in the Early Treatment Diabetic Retinopathy Study, and about half of the vitrectomies were preformed secondary to TRD [1,5]. Retinal injury due to iatrogenic causes occurs in 20-60% of cases during TRD operations [1]. One of the intra-operative complications of TRD release is iatrogenic tears, which are thought to be due to detachment propagations. This occurs when traction released in one vector by a sub-optimal cut leaves another vector unopposed and creates a tearing force along the retina.

Materials and Methods
Internal Review Board approval was obtained for a retrospective chart review of patients with a diagnosis of tractional retinal detachment (TRD). Medical records were reviewed by one investigator to limit patient information exposure. Only deidentified OCT images were used in analysis. A total of 50 Charts were reviewed for inclusion. Of those 50 charts, 5 were selected based on the amount of the TRD that was captured by the OCT. The retrospective nature of the study dictated that central involving TRDs be used, as peripheral TRDs are usually not captured by routine OCT. A single final image was selected for final stress analysis based on appropriateness of the OCT scan of the TRD.
A three-dimensional computational model of the retinal-sclera segment was constructed based on anatomic knowledge and the OCT shown in Figure 1. The radius of the retinal layer was 12 mm, with the thickness of 0.25 mm. A scope of 2 mm × 2.5 mm was selected with the attached sclera. The material properties of the tissue were adopted from our previous work [6]. A three-dimensional reconstruction of an OCT analysis using Zeiss Cirrus 5000 image derived from a patient-specific OCT scan, a traction force was ap-

Discussion
The highest stress values were found at the peak of the detachment. This was expected, as the retinal tissue at the peak of the detachment has the greatest curvature induced by the contract-

Future Directions
This study represents the preliminary stage of force traction mapping and will need more data to assess the validity of the analysis. Utilization of this technique for preoperative or intraoperative planning could improve outcomes of TRD release by optimizing the surgical approach and reducing iatrogenic tears. Force traction maps could also be used as visual aids to improved patient education. This is because they are more visually simplistic than a standard OCT scan of a TRD.