Rohan J. Shah

In vitro assessment of image-guided otologic surgery: Submillimeter accuracy within the region of the temporal bone

OBJECTIVES: Application of image-guided surgery to otology has been limited by the need for sub-millimeter accuracy via a fiducial system that is easily usable (noninvasive and nonobstructive). METHODS: A dental bite-block was fitted with a rigid frame with 7 fiducial markers surrounding each external ear. The temporal bones of 3 cadaveric skulls were removed and replaced with surgical targets arranged in a bulls-eye pattern about the centroid of each temporal bone. The surgical targets were identified both within CT scans and in physical space using an infrared optical tracking system. The difference between positions in CT space versus physical space was calculated as target registration error. RESULTS: A total of 234 independent target registration errors were calculated. Mean ± standard deviation = 0.73 mm ± 0.25 mm. CONCLUSIONS: These findings show that image-guided otologic surgery with submillimeter accuracy is achievable with a minimally invasive fiducial frame. SIGNIFICANCE: In vivo validation of the system is ongoing. With such validation, this system may facilitate clinically applicable image-guided otologic surgery. EBM rating: A.

Submillimetric target-registration error using a novel, non-invasive fiducial system for image-guided otologic surgery.

Objective: Otologic surgery is undertaken to treat ailments of the ear, including persistent infections, hearing loss, vertigo, and cancer. Typically performed on otherwise-healthy patients in outpatient facilities, the application of image-guided surgery (IGS) has been limited because accurate (<1 mm), non-invasive fiducial systems for otologic surgery have not been available. We now present such a fiducial system. Methods: A dental bite-block was fitted with a custom-designed rigid frame with 7 fiducial markers surrounding each external ear. The bones containing the ear (i.e., the temporal bones) of 3 cadaveric skulls were removed and replaced with discs containing 13 surgical targets arranged in a cross-hair pattern about the centroid of each ear. The surgical targets (26/skull) and fiducial markers (14/skull) were identified both within CT scans using a published algorithm and in physical space using an infrared optical tracking system. Fiducial registration error (FRE), fiducial localization error (FLE), and target registration error (TRE) were calculated. Results: For all trials, root mean square FRE=0.66, FLE=0.72, and TRE=0.77mm. The mean TRE for n=234 independent targets was 0.73 with a standard deviation of 0.25mm. Conclusions: Using a novel, non-invasive fiducial system (the EarMark™), submillimetric accuracy was repeatably achieved. This system will facilitate image-guided otologic surgery.

Evaluation of microsurgical tasks with OCT-guided and/or robot-assisted ophthalmic forceps

Real-time intraocular optical coherence tomography (OCT) visualization of tissues with surgical feedback can enhance retinal surgery. An intraocular 23-gauge B-mode forward-imaging co-planar OCT-forceps, coupling connectors and algorithms were developed to form a unique ophthalmic surgical robotic system. Approach to the surface of a phantom or goat retina by a manual or robotic-controlled forceps, with and without real-time OCT guidance, was performed. Efficiency of lifting phantom membranes was examined. Placing the co-planar OCT imaging probe internal to the surgical tool reduced instrument shadowing and permitted constant tracking. Robotic assistance together with real-time OCT feedback improved depth perception accuracy. The first-generation integrated OCT-forceps was capable of peeling membrane phantoms despite smooth tips.

Prospective Retinal and Optic Nerve Vitrectomy Evaluation (PROVE) Study: Twelve-Month Findings

PURPOSE To report 1-year outcomes of the Prospective Retinal and Optic Nerve Vitrectomy Evaluation study. DESIGN Prospective, controlled, observational study. PARTICIPANTS Eighty eyes of 40 participants undergoing pars plana vitrectomy for epiretinal membrane (ERM), macular hole (MH), or vitreous opacities. METHODS Enrolled participants underwent baseline evaluation of the study (surgical) and fellow (control) eyes by a masked fellowship-trained glaucoma specialist; evaluation included intraocular pressure (IOP; Goldmann applanation and Tono-Pen), central corneal thickness, gonioscopy, and cup-to-disc ratio measurement. Baseline testing included bilateral color fundus and optic disc photography, fundus autofluorescence, automated perimetry, and optical coherence tomography (OCT) of the macula and optic nerve. Evaluations were repeated at 3 months and 1 year after surgery. MAIN OUTCOME MEASURES The primary outcome measure was changes in peripapillary retinal nerve fiber layer (pRNFL) thickness. Secondary outcomes included changes in macular thickness and IOP. RESULTS Thirty-eight of 40 patients completed 1 year of follow-up. Mean visual acuity (VA) improved in study eyes from baseline (P = 0.003) but remained worse than fellow eyes (P<0.001). Study eyes had thinner inferior pRNFL thickness (114±16.8 μm) compared with fellow eyes (123±14.7 μm; P = 0.004). Mean IOP difference between study eyes and fellow eyes increased from baseline to 1 year. At 1 year, MH study eyes had higher mean IOP (16.0±3.7 mmHg) compared with fellow eyes (14.8±3.4 mmHg; P = 0.08). Mean IOP for pseudophakic study eyes increased from 14.5±3.2 mmHg at baseline to 16.0±2.8 mmHg at 1 year (P = 0.04). Central subfield thickness (CST) and cube volume decreased in study eyes at 1 year but remained greater than that of fellow eyes (P<0.05). Reduction in CST from baseline correlated with degree of VA improvement (P<0.05). Mean deviation (MD) improved in ERM study eyes at 1 year when compared with baseline (-2.2 vs. -4.0; P = 0.02) but remained worse than fellow eyes (-1.2; P = 0.002). CONCLUSIONS One year after vitrectomy, VA, CST, and MD improved in study eyes but not to the level of fellow eyes. Inferior pRNFL thickness decreased in study eyes. Reduction in CST from baseline correlated with degree of VA improvement. Pseudophakic study eyes demonstrated increased IOP when compared with baseline.

The Safety, Pharmacokinetics, and Efficacy of Intraocular Celecoxib

PURPOSE To determine safety, pharmacokinetics, and anti-inflammatory effects of intraocular celecoxib. METHODS The right eye of animals was injected with 1.5, 3, or 6 mg celecoxib prepared in dimethyl sulfoxide (DMSO). Left eyes served as controls and received 0.1 mL DMSO. Electroretinograms (ERG) were obtained at baseline and at 1, 4, and 12 weeks, and eyes were enucleated afterward for histopathologic analysis. For pharmacokinetics, 3 mg celecoxib was injected, and vitreous and retina/choroid drug levels were then analyzed at specific time points. For efficacy, 1 μg lipopolysaccharide was injected to induce inflammation; the right eye was then injected with 3 mg celecoxib (six eyes) or 2 mg triamcinolone acetonide (six eyes) and the left eye with saline. Twenty-four hours later, aqueous fluid was removed, and total leukocyte concentration and prostaglandin E2 (PGE2) concentration were determined. RESULTS Histologic and ERG studies demonstrated no signs of retinal or optic nerve toxicity. After a single 3-mg injection, vitreous (0.06 μg/mL) and retina/choroid (132.31 μg/g) celecoxib concentrations at 8 weeks exceeded median inhibitory concentration. Treatment with celecoxib and triamcinolone significantly reduced total leukocyte count by 40% (P = 0.02) and 31% (P = 0.01), respectively. Reduction in PGE2 levels paralleled reduction in leukocyte counts (P < 0.05). There was no increase in intraocular pressure, but cataract formation was observed at higher concentrations. CONCLUSIONS Intraocular injection of celecoxib appeared to be nontoxic and demonstrated excellent penetration into the retina/choroid and sustained drug levels out to 8 weeks. Celecoxib demonstrated potent anti-inflammatory effects, but there was an association with cataract formation at higher doses.

Two-Year Anatomical and Functional Outcomes After Macular Hole Surgery: A Prospective, Controlled Study

BACKGROUND AND OBJECTIVE To determine 2-year anatomical and functional outcomes after macular hole (MH) surgery. PATIENTS AND METHODS The surgical eye (SE) and fellow eye (FE) of 10 patients undergoing MH surgery were examined preoperatively and at 3, 12, and 24 months postoperatively. Retinal nerve fiber layer (RNFL), external limiting membrane (ELM), inner segment/outer segment (IS/OS) junction, cone outer-segment tips (COST) line, and ganglion cell inner plexiform layer (GCIPL) thickness were analyzed on spectral-domain optical coherence tomography. RESULTS Inferior peripapillary RNFL was thinner in the SE at 110 ± 12.2 versus 123 ± 9.82 for FE (P < .05). Defect size in ELM (r = 0.61; P < .001), IS/ OS (r = 0.67; P < .001) junction, and COST (r = .67; P < .001) line correlated with visual recovery. Average GCIPL was thinner in SE compared to FE (P < .05). CONCLUSION Eyes after MH repair demonstrated inferior RNFL and GCIPL thinning. Defect size in ELM, IS/OS junction, and COST line predicted visual recovery.

Ocular findings at initial pan retinal photocoagulation for proliferative diabetic retinopathy predict the need for future pars plana vitrectomy.

Purpose: To determine the 1-year and 2-year likelihood of vitrectomy in diabetic patients undergoing initial pan retinal photocoagulation (PRP). Methods: Diabetic eyes receiving initial PRP for proliferative diabetic retinopathy (PDR) were analyzed to determine their risk for vitrectomy based on clinical findings. Results: In total, 374 eyes of 272 patients were analyzed. The percentage of eyes undergoing vitrectomy 1 year and 2 years following initial PRP was 19.1% and 26.2%, respectively. Of the eyes in Group 1 (PDR alone), Group 2 (PDR and vitreous hemorrhage), and Group 3 (PDR and iris neovascularization, vitreous hemorrhage with traction or fibrosis, or fibrosis alone), the percentage receiving pars plana vitrectomy at 1 year and 2 years was 9.73% (18/185) and 15.7% (29/185), 26.9% (43/160) and 34.4% (55/160), and 37.9% (11/29) and 48.3% (14/29), respectively. Eyes in Group 2 had 2.78 times greater likelihood (P < 0.0001) and eyes in Group 3 had 3.54 times higher likelihood (P < 0.0001) of requiring pars plana vitrectomy within 2 years than those with PDR alone. Conclusion: Eyes receiving PRP for PDR with associated hemorrhage or traction were more likely to undergo pars plana vitrectomy within 1 year and 2 years following initial PRP compared with eyes with only PDR, providing important prognostic information for PRP-naive patients.

Endoscopic-approach development for minimally invasive orbital surgery

Purpose: Orbital tumors and pseudotumor cerebri are sometimes treated with surgical approaches. Our previous studies suggest that potentially endoscopy may be useful for minimally invasive orbital surgery. This study proposed to improve the approach technique for accessing the posterior orbital space via endoscopy, as well as assess visibility improvements with CO2 insufflation to posterior orbital tissues. Methods: An inferior transconjunctival approach accessed the posterior orbital space in non-survival pigs. Various guidance tubes were compared to assess ability to guide the endoscope to the posterior orbit with the greatest ease and visibility. FEL energy application (6.1 &mgr;m, 2.7 ± 0.5 mJ, 30 Hz, delivered via glass-hollow waveguide) was attempted via endoscopy. The effect of CO2 gas insufflation was assessed by analyzing visibility of the stuctures before and after CO2 application. Results: The posterior orbit was accessed via endoscopy in all except the first attempted eye. A beveled transparent butyrate tube provided the best guidance for the endoscope and an opaque metal tube provided the worst guidance. The optic nerve was encountered and FEL energy was applied with the butyrate tube in 8 orbits. Visibility was adequate without CO2 insufflation, and did not improve with CO2. Conclusions: The posterior orbit was successfully accessed using endoscopy. The optic nerve was exposed and treated with FEL energy. CO2 insufflation did not further enhance visibility in this study. Application of endoscopy for posterior orbital procedures is feasible, but extreme surgical care is required and further study with human cadaveric eyes is needed.