Lensectomy as treatment for refractory or progressive retinopathy of prematurity narrow-angle glaucoma.

We present the case of a patient with a history of laser-treated retinopathy of prematurity (ROP) who developed narrow angles and intermittent angle closure. Despite laser peripheral iridotomy/iridoplasty, 1 year later, the patient had recurrent narrowing that resolved following clear lens extraction with intraocular lens placement. This case highlights the importance of continued monitoring for narrow angles in patients with ROP history.

A Review of Robotic and OCT-Aided Systems for Vitreoretinal Surgery.

The introduction of the intraocular vitrectomy instrument by Machemer et al. has led to remarkable advancements in vitreoretinal surgery enabling the limitations of human physiologic capabilities to be reached. To overcome the barriers of perception, tremor, and dexterity, robotic technologies have been investigated with current advancements nearing the feasibility for clinical use. There are four categories of robotic systems that have emerged through the research: (1) handheld instruments with intrinsic robotic assistance, (2) hand-on-hand robotic systems, (3) teleoperated robotic systems, and (4) magnetic guidance robots. This review covers the improvements and the remaining needs for safe, cost-effective clinical deployment of robotic systems in vitreoretinal surgery.

Surgical management of large bilateral epibulbar dermoids with autologous oral mucous membrane transplantation.

PURPOSE: To report the surgical management of extensive epibulbar dermoids with autologous oral mucous membrane transplantation. OBSERVATIONS: While rare, extensive dermoids that encroach upon the visual axis carry a poor prognosis. We report the case of a 7-week old premature male infant who presented with large bilateral epibulbar dermoids obscuring the visual axis. He was treated first with sequential bilateral optical iridectomies under the clearest corneal areas, followed several months later by sequential dermoid excision and amniotic membrane transplantation in each eye. He subsequently underwent autologous "simple" oral mucosal epithelial transplantation (SOMET) as well as strabismus surgery. Conclusions and Importance: Here we present the first case, to the best of our knowledge, of the use of SOMET in managing post-operative pseudopterygium following dermoid excision. To our knowledge it is the also the first application of this technique in a young pediatric patient. A good clinical outcome may be achieved with SOMET, which may offer a minimally invasive alternative to other traditional modalities.

Three-Year Findings on Intraocular Pressure Changes in The Prospective Retinal and Optic Nerve Vitrectomy Evaluation (PROVE) Study.

BACKGROUND AND OBJECTIVE: This paper reports 3-year intraocular pressure (IOP) outcomes of the Prospective Retinal and Optic Nerve Vitrectomy Evaluation (PROVE) study. PATIENTS AND METHODS: The prospective, controlled, observational study included 80 eyes of 40 participants undergoing routine pars plana vitrectomy. Study patients underwent preoperative evaluation and multimodal testing of the study (surgical) and fellow (control) eye. This testing was repeated at 3 months postoperatively and then annually for 3 years. RESULTS: Thirty-two of 40 patients (80%) completed 3-year follow-up. At 3 years postoperatively, there was no difference in IOP measurements in surgical eyes overall from baseline (P = .36). Subgroup analysis of pseudophakic eyes at baseline showed a significant elevation in IOP from 14.3 mm Hg ± 2.9 mm Hg at baseline to 16.8 mm Hg ± 3.2 mm Hg at 3-year follow-up (P < .029). Fellow eyes did not experience a significant change from baseline. CONCLUSION: The authors' 3-year results show that IOP is consistently and significantly elevated in pseudophakic eyes compared to baseline following routine vitrectomy. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:371-376.].

Short-term Optic Disc Cupping Reversal in a Patient With Mild Juvenile Open-angle Glaucoma Due to Early Idiopathic Intracranial Hypertension.

PURPOSE: The purpose of this study was to report a case of optic disc cupping reversal in an adult without significant intraocular pressure-lowering treatment. PATIENT: A 20-year-old female with a history of mild juvenile open-angle glaucoma who developed subjective blurred vision and a decrease in cupping of her optic discs. RESULTS: Dilated examination demonstrated decreased cup-to-disc ratios in both eyes with a slight blurring of the disc margin in the right eye. The appearance of both optic discs returned to baseline after weight loss therapy. CONCLUSIONS: An unexplained reduction of optic nerve cup-to-disc ratio should prompt a workup for other etiologies, such as increased intracranial pressure. Baseline photographs not subjected to computerized scan obsolescence are extremely useful in monitoring the long-term appearance of asymmetric optic discs as an adjunct to the clinical examination.

Optic nerve sheath fenestration using a Raman-shifted alexandrite laser.

BACKGROUND AND OBJECTIVE: Optic nerve sheath fenestration is an established procedure for relief of potentially damaging overpressure on the optic nerve resulting from idiopathic intracranial hypertension. Prior work showed that a mid-IR free-electron laser could be delivered endoscopically and used to produce an effective fenestration. This study evaluates the efficacy of fenestration using a table-top mid-IR source based on a Raman-shifted alexandrite (RSA) laser. STUDY DESIGN/MATERIALS AND METHODS: Porcine optic nerves were ablated using light from an RSA laser at wavelengths of 6.09, 6.27, and 6.43 µm and pulse energies up to 3 mJ using both free-space and endoscopic beam delivery through 250-µm I.D. hollow-glass waveguides. Waveguide transmission was characterized, ablation thresholds and etch rates were measured, and the efficacy of endoscopic fenestration was evaluated for ex vivo exposures using both optical coherence tomography and histological analysis. RESULTS: Using endoscopic delivery, the RSA laser can effectively fenestrate porcine optic nerves. Performance was optimized at a wavelength of 6.09 µm and delivered pulse energies of 0.5-0.8 mJ (requiring 1.5-2.5 mJ to be incident on the waveguide). Under these conditions, the ablation threshold fluence was 0.8 ± 0.2 J/cm(2) , the ablation rate was 1-4 µm/pulse, and the margins of ablation craters showed little evidence of thermal or mechanical damage. Nonetheless, nominally identical exposures yielded highly variable ablation rates. This led to fenestrations that ranged from too deep to too shallow-either damaging the underlying optic nerve or requiring additional exposure to cut fully through the sheath. Of 48 excised nerves subjected to fenestration at 6.09 µm, 16 ex vivo fenestrations were judged as good, 23 as too deep, and 9 as too shallow. CONCLUSIONS: Mid-IR pulses from the RSA laser, propagated through a flexible hollow waveguide, are capable of cutting through porcine optic nerve sheaths in surgically relevant times with reasonable accuracy and low collateral damage. This can be accomplished at wavelengths of 6.09 or 6.27 µm, with 6.09 µm slightly preferred. The depth of ex vivo fenestrations was difficult to control, but excised nerves lack a sufficient layer of cerebrospinal fluid that would provide an additional margin of safety in actual patients.

Efficacy and predictability of soft tissue ablation using a prototype Raman-shifted alexandrite laser.

Previous research showed that mid-infrared free-electron lasers could reproducibly ablate soft tissue with little collateral damage. The potential for surgical applications motivated searches for alternative tabletop lasers providing thermally confined pulses in the 6- to-7-µm wavelength range with sufficient pulse energy, stability, and reliability. Here, we evaluate a prototype Raman-shifted alexandrite laser. We measure ablation thresholds, etch rates, and collateral damage in gelatin and cornea as a function of laser wavelength (6.09, 6.27, or 6.43 µm), pulse energy (up to 3 mJ/pulse), and spot diameter (100 to 600 µm). We find modest wavelength dependence for ablation thresholds and collateral damage, with the lowest thresholds and least damage for 6.09 µm. We find a strong spot-size dependence for all metrics. When the beam is tightly focused (~100-µm diameter), ablation requires more energy, is highly variable and less efficient, and can yield large zones of mechanical damage (for pulse energies>1 mJ). When the beam is softly focused (~300-µm diameter), ablation proceeded at surgically relevant etch rates, with reasonable reproducibility (5% to 12% within a single sample), and little collateral damage. With improvements in pulse-energy stability, this prototype laser may have significant potential for soft-tissue surgical applications.

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.

Primary cilia signaling mediates intraocular pressure sensation.

Lowe syndrome is a rare X-linked congenital disease that presents with congenital cataracts and glaucoma, as well as renal and cerebral dysfunction. OCRL, an inositol polyphosphate 5-phosphatase, is mutated in Lowe syndrome. We previously showed that OCRL is involved in vesicular trafficking to the primary cilium. Primary cilia are sensory organelles on the surface of eukaryotic cells that mediate mechanotransduction in the kidney, brain, and bone. However, their potential role in the trabecular meshwork (TM) in the eye, which regulates intraocular pressure, is unknown. Here, we show that TM cells, which are defective in glaucoma, have primary cilia that are critical for response to pressure changes. Primary cilia in TM cells shorten in response to fluid flow and elevated hydrostatic pressure, and promote increased transcription of TNF-α, TGF-ß, and GLI1 genes. Furthermore, OCRL is found to be required for primary cilia to respond to pressure stimulation. The interaction of OCRL with transient receptor potential vanilloid 4 (TRPV4), a ciliary mechanosensory channel, suggests that OCRL may act through regulation of this channel. A novel disease-causing OCRL allele prevents TRPV4-mediated calcium signaling. In addition, TRPV4 agonist GSK 1016790A treatment reduced intraocular pressure in mice; TRPV4 knockout animals exhibited elevated intraocular pressure and shortened cilia. Thus, mechanotransduction by primary cilia in TM cells is implicated in how the eye senses pressure changes and highlights OCRL and TRPV4 as attractive therapeutic targets for the treatment of glaucoma. Implications of OCRL and TRPV4 in primary cilia function may also shed light on mechanosensation in other organ systems.

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.

Miniature forward-imaging B-scan optical coherence tomography probe to guide real-time laser ablation.

BACKGROUND AND OBJECTIVE: Investigations have shown that pulsed lasers tuned to 6.1 µm in wavelength are capable of ablating ocular and neural tissue with minimal collateral damage. This study investigated whether a miniature B-scan forward-imaging optical coherence tomography (OCT) probe can be combined with the laser to provide real-time visual feedback during laser incisions. STUDY DESIGN/METHODS AND MATERIALS: A miniature 25-gauge B-scan forward-imaging OCT probe was developed and combined with a 250 µm hollow-glass waveguide to permit delivery of 6.1 µm laser energy. A gelatin mixture and both porcine corneal and retinal tissues were simultaneously imaged and lased (6.1 µm, 10 Hz, 0.4-0.7 mJ) through air. The ablation studies were observed and recorded in real time. The crater dimensions were measured using OCT imaging software (Bioptigen, Durham, NC). Histological analysis was performed on the ocular tissues. RESULTS: The combined miniature forward-imaging OCT and mid-infrared laser-delivery probe successfully imaged real-time tissue ablation in gelatin, corneal tissue, and retinal tissue. Application of a constant number of 60 pulses at 0.5 mJ/pulse to the gelatin resulted in a mean crater depth of 123 ± 15 µm. For the corneal tissue, there was a significant correlation between the number of pulses used and depth of the lased hole (Pearson correlation coefficient = 0.82; P = 0.0002). Histological analysis of the cornea and retina tissues showed discrete holes with minimal thermal damage. CONCLUSIONS: A combined miniature OCT and laser-delivery probe can monitor real-time tissue laser ablation. With additional testing and improvements, this novel instrument has the future possibility of effectively guiding surgeries by simultaneously imaging and ablating tissue.

Preliminary Design and Evaluation of a B-Scan OCT-Guided Needle.

Real-time intraoperative B-scan optical coherence tomography (OCT) visualization of intraocular tissues is a desired ophthalmic feature during retinal procedures. A novel intraocular 25-gauge B-mode forward-imaging OCT probe was combined with a 36-gauge needle into a prototype instrument. Imaging of the needle tip itself and the effects of saline injection into a gelatin phantom were performed. A combined B-scan forward-imaging OCT-needle prototype was capable of real-time-imaging of saline injection into a gelatin phantom. Additional future miniaturization may permit this instrument to be an adjunctive realtime imaging and procedure tool for vitreoretinal surgery.

Prospective Retinal and Optic Nerve Vitrectomy Evaluation (PROVE) study: findings at 3 months.

BACKGROUND: The purpose of this paper is to report the 3-month findings of the Prospective Retinal and Optic Nerve Vitrectomy Evaluation (PROVE) study. METHODS: Eighty eyes of 40 participants undergoing vitrectomy were enrolled. Participants underwent baseline evaluation of the study (surgical) and fellow (control) eye that included: intraocular pressure, central corneal thickness, gonioscopy, cup-to-disc ratio measurement, color fundus and optic disc photography, automated perimetry, and optical coherence tomography of the macula and optic nerve. Evaluation was repeated at 3 months. Main outcome measures were changes in macula and retinal nerve fiber layer (RNFL) thickness and intraocular pressure. RESULTS: All participants completed follow-up. Mean cup-to-disc ratio of study and fellow eyes at baseline was 0.43 ± 0.2 and 0.46 ± 0.2, respectively, and 13% of participants had undiagnosed narrow angles. There was no significant change in intraocular pressure, cup-to-disc ratio, or pattern standard deviation in study eyes compared with baseline or fellow eyes at 3 months. Vision improved in all study eyes at 3 months compared with baseline (P = 0.013), but remained significantly worse than fellow eyes (P < 0.001). Central subfield and temporal peripapillary RNFL thickness were significantly greater in eyes with epiretinal membrane (P < 0.05), and resolution after surgery correlated with visual improvement (P < 0.05). CONCLUSION: The 3-month results do not indicate any increased risk for open-angle glaucoma but suggest that a relatively high percentage of eyes may be at risk of angle closure glaucoma. Temporal RNFL thickness and central subfield were increased in eyes with epiretinal membrane, and resolution correlated with degree of visual recovery.

Miniature real-time intraoperative forward-imaging optical coherence tomography probe.

Optical coherence tomography (OCT) has a tremendous global impact upon the ability to diagnose, treat, and monitor eye diseases. A miniature 25-gauge forward-imaging OCT probe with a disposable tip was developed for real-time intraoperative ocular imaging of posterior pole and peripheral structures to improve vitreoretinal surgery. The scanning range was 2 mm when the probe tip was held 3-4 mm from the tissue surface. The axial resolution was 4-6 µm and the lateral resolution was 25-35 µm. The probe was used to image cellophane tape and multiple ocular structures.

Long-term results of combined endoscope-assisted pars plana vitrectomy and glaucoma tube shunt surgery.

PURPOSE: To assess outcomes after endoscope-assisted pars plana vitrectomy with concurrent pars plana tube shunt placement. METHODS: Records of 18 adult patients (19 eyes) with uncontrolled chronic angle-closure glaucoma associated with corneal opacification or fibrosed pupils were retrospectively reviewed. All eyes underwent endoscope-assisted pars plana vitrectomy with Baerveldt tube shunt placement into the vitreous cavity between 1997 and 2005. Intraocular pressure reduction, glaucoma medication reduction, complications, and visual acuity were analyzed. RESULTS: Mean follow-up duration was 62 months (range, 10-106 months). Mean preoperative intraocular pressure was 31.3 ± 10.5 mmHg on 3.4 ± 1.0 glaucoma medications. Intraocular pressure was significantly reduced at each postoperative time point examined. In the 17 eyes without phthisis, intraocular pressure was significantly reduced at the final follow-up examination to a mean of 11.4 ± 2.9 mmHg (P < 0.0001) on 1.3 ± 1.2 medications (P < 0.0001). No complications occurred in 14 of 19 eyes. Postoperatively, best-attained visual acuity improved in 14 of 19 eyes, remained unchanged in 4 of 19 eyes, and was reduced in 1 of 19 eyes. CONCLUSION: Combined endoscope-assisted pars plana vitrectomy with placement of a Baerveldt tube shunt into the vitreous cavity is a useful intervention in patients with uncontrolled chronic angle-closure glaucoma, media opacities, and limited surgical options.

Endoscopic free electron laser technique development for minimally invasive optic nerve sheath fenestration.

PURPOSE: This study proposed to develop a technique for efficiently accessing the posterior orbital space using endoscopy and attempted application of free electron laser (FEL) energy, biopsy forceps, electrocautery, and CO(2) insufflation to posterior orbital tissues. METHODS: Through an inferior transconjunctival incision, access to the posterior orbital space was attempted in 14 eyes of 7 non-survival pigs. FEL energy (6.1 microm, 30 Hz, delivered via 250 microm hollow-glass waveguide), biopsy forceps, and monopolar electrocautery application were endoscopically attempted in the posterior orbit. CO(2) gas insufflation effects were assessed by analyzing arterial blood gases at 30-minute intervals for 1.5 hours. RESULTS: The posterior orbit was accessed in 13 of 14 eyes, the optic nerve was encountered, and FEL energy was applied in 8 of 14 eyes. Use of biopsy forceps and electrocautery were successful. Although ANOVA results for arterial blood gas changes were not statistically significant, visibility was adequate without CO(2) insufflation. CONCLUSIONS: The posterior orbit was endoscopically accessed and the optic nerve was exposed and successfully treated with FEL energy. CO(2) insufflation did not alter blood gases, but did not further enhance visibility in this study.

Mid infrared optical parametric oscillator (OPO) as a viable alternative to tissue ablation with the free electron laser (FEL).

BACKGROUND AND OBJECTIVES: Investigations with a Mark-III free electron laser, tuned to 6.45 microm in wavelength have demonstrated minimal collateral damage and high ablation yield in ocular and neural tissues. While the use of mid-IR light produced by the free electron laser (FEL) has shown much promise for surgical applications, further advances are limited due the high costs of its use. Further investigation and widespread clinical use of six-micron radiation requires the development of an alternative laser source. In this research, we compared a Mark-III FEL and an Er:YAG pumped ZGP-OPO with respect to the effect of pulse duration on ablation efficiency and thermal damage on porcine cornea. STUDY DESIGN/MATERIALS AND METHODS: A five by seven grid of craters was made about the center of each cornea. Craters were made with a 60-microm spotsize with a 500-microm spacing. Ablation craters were made using 50 pulses per crater at approximately three times the ablation threshold (for water). Histological analysis was used to determine crater depth and thermal damage. RESULTS: The average zone of thermal damage at 6.1 microm was found to be 4.1 microm for the optical parametric oscillator (OPO) and 5.4 microm for the FEL. At 6.45 microm, the damaged zone was 7.2 microm for the OPO and 7.2 microm for the FEL. At 6.73 microm, the damaged zone was 6.3 microm for the OPO and 7.6 microm+/-0.3 microm for the FEL. CONCLUSIONS: The OPO caused similar or significantly less thermal damage in porcine cornea when compared with the FEL while generating significantly deeper craters. We determined that the ZGP-OPO has much promise as a bench-top replacement for the FEL for soft tissue ablation.

Optic nerve sheath fenestration with endoscopic accessory instruments versus the free electron laser (FEL).

BACKGROUND AND OBJECTIVE: The free electron laser (FEL) can efficiently produce an optic nerve sheath fenestration using an endoscopic approach. To develop a surgical protocol, this study compared effectiveness of available accessory endoscopic instruments to endoscopic FEL delivery effectiveness in producing optic nerve sheath fenestrations. STUDY DESIGN/MATERIALS AND METHODS: An endoscope was used to perform optic nerve sheath fenestrations on goat optic nerves. Accessory endoscopic instruments and glass-hollow waveguides (250 and 320 microm in diameter) were inserted into the instrument channel for comparison. FEL energy (6.45 microm, 30 Hz) was delivered to the tissue through the waveguides and histological analysis was performed. RESULTS: The endoscopic instruments alone were unable to incise the optic nerve sheath. The FEL successfully incised the sheath and the biopsy forceps extricated the circular flap. CONCLUSIONS: Endoscopic optic nerve sheath fenestration using FEL energy followed by biopsy forceps for sheath extrication produced good results, thereby creating a feasible protocol for optic nerve sheath fenestration.

The effect of free-electron laser pulse structure on mid-infrared soft-tissue ablation: biological effects.

Previous studies have shown that changing the pulse structure of the free electron laser (FEL) from 1 to 200 ps and thus reducing the peak irradiance of the micropulse by 200 times had little or no effect on both the ablation threshold radiant exposure and the ablated crater depth for a defined radiant exposure. This study focuses on the ablation mechanism at 6.1 and 6.45 microm with an emphasis on the role of the FEL pulse structure. Three different experiments were performed to gain insight into this mechanism. The first was an analysis of the ablation plume dynamics observed for a 1 ps micropulse compared with a 200 ps micropulse as seen through bright-field analysis. Negligible differences are seen in the size, but not the dynamics of ablation, as a result of this imaging. The second experiment was a histological analysis of corneal and dermal tissue to determine whether there is less thermal damage associated with one micropulse duration versus another. No significant difference was seen in the extent of thermal damage on either canine cornea or mouse dermis for the micropulse durations studied at either wavelength. The final set of experiments involved the use of mass spectrometry to determine whether amide bond breakage could occur in the proteins present in tissue as a result of direct absorptions of mid-infrared light into the amide I and amide II absorption bands. This analysis showed that there was no amide bond breakage due to irradiation at 6.45 microm on protein.

Development of an orbital endoscope for use with the free electron laser.

PURPOSE: To explore the feasibility of designing, constructing, and testing an orbital endoscope for use with the free electron laser (FEL). METHODS: An experimental study with an author-designed laser delivery system through an endoscope was conducted. Two adult pig cadavers and 6 fresh human cadavers had orbital endoscopy performed to develop a method of optic nerve sheath fenestration (ONSF) with the FEL. Twelve orbits were used to develop the surgical procedure by comparing visualization media and surgical technique. In the first 7 trials, a different variable was changed; the procedure was then refined in the human cadaver experiments. An ONSF was performed with the FEL (6.45 microm, 30 Hz, 2 to 3 mJ, 250-microm spot size) through a glass hollow wave guide introduced through an endoscope in 4 human cadaver orbits. RESULTS: Visualization of the orbital structures was clearest with carbon dioxide; sodium hyaluronate did not displace the fat, and saline hydrated the orbital fat. Biopsy forceps alone did not produce a dural window in the four trials that used the forceps. A dural window was made by using the FEL through a glass hollow wave guide adapted to the Olympus HYF-XP endoscope in the second, third, fifth, and sixth human trials with the FEL. Histologic evidence of the ONSF was produced. CONCLUSIONS: A hollow wave guide capable of transmitting the FEL through an endoscope was successfully constructed. ONSF with the FEL applied through an endoscope is technically feasible. Additional studies are currently examining techniques to improve intraorbital endoscopy.