A force measurement platform for a vitreoretinal surgical simulator using an artificial eye module integrated with a quartz crystal resonator.

To provide quantitative feedback on surgical progress to ophthalmologists practicing inner limiting membrane (ILM) peeling, we developed an artificial eye module comprising a quartz crystal resonator (QCR) force sensor and a strain body that serves as a uniform force transmitter beneath a retinal model. Although a sufficiently large initial force must be loaded onto the QCR force sensor assembly to achieve stable contact with the strain body, the highly sensitive and wide dynamic-range property of this sensor enables the eye module to detect the slight forceps contact force. A parallel-plate strain body is used to achieve a uniform force sensitivity over the 4-mm-diameter ILM peeling region. Combining these two components allowed for a measurable force range of 0.22 mN to 29.6 N with a sensitivity error within -11.3 to 4.2% over the ILM peeling area. Using this eye module, we measured the applied force during a simulation involving artificial ILM peeling by an untrained individual and compensated for the long-term drift of the obtained force data using a newly developed algorithm. The compensated force data clearly captured the characteristics of several types of motion sequences observed from video recordings of the eye bottom using an ophthalmological microscope. As a result, we succeeded in extracting feature values that can be potentially related to trainee skill level, such as the mean and standard deviation of the pushing and peeling forces, corresponding, in the case of an untrained operator, to 122.6 ± 95.2 and 20.4 ± 13.2 mN, respectively.

Bionic eye system mimicking microfluidic structure and intraocular pressure for glaucoma surgery training.

Among increasing eye diseases, glaucoma may hurt the optic nerves and lead to vision loss, the treatment of which is to reduce intraocular pressure (IOP). In this research, we introduce a new concept of the surgery simulator for Minimally Invasive Glaucoma Surgery (MIGS). The concept is comprised of an anterior eye model and a fluidic circulatory system. The model made of flexible material includes a channel like the Schlemm's canal (SC) and a membrane like the trabecular meshwork (TM) covering the SC. The system can monitor IOP in the model by a pressure sensor. In one of the MIGS procedures, the TM is cleaved to reduce the IOP. Using the simulator, ophthalmologists can practice the procedure and measure the IOP. First, considering the characteristics of human eyes, we defined requirements and target performances for the simulator. Next, we designed and manufactured the prototype. Using the prototype, we measured the IOP change before and after cleaving the TM. Finally, we demonstrated the availability by comparing experimental results and target performances. This simulator is also expected to be used for evaluations and developments of new MIGS instruments and ophthalmic surgery robots in addition to the surgical training of ophthalmologists.

Recent trends in vitreoretinal surgery: a nationwide database study in Japan, 2010-2017.

PURPOSE: We clarified recent trends in vitreoretinal surgery in Japan, which is a rapidly aging country. STUDY DESIGN: Retrospective cohort study. METHODS: We used the Diagnostic Procedure Combination database (2010-2017), a national inpatient database in Japan. Patients undergoing vitreoretinal surgery were included. We measured the number of surgeries stratified by procedures, diagnoses, age categories, and combined cases of cataract surgery per fiscal year. We also considered changes in the Japanese population. RESULTS: From 2010 to 2017, the total number of vitreoretinal surgeries per fiscal year increased by 7.8% (from 36,988 to 39,873). Among the diagnoses categories, epiretinal membrane (ERM) increased by 71%, rhegmatogenous retinal detachment (RRD) with pars plana vitrectomy (PPV) by 50%, and macular hole (MH) by 12% throughout the observed period. Diabetic retinopathy (DR) decreased by 20%, RRD with scleral buckling (SB) by 40%, and vitreous hemorrhage (VH) by 10%. We observed remarkable increases in ERM among patients in their 60s and 70s, in MH in their 70s and 80s, and in RRD with PPV in their 50s and 60s. We observed remarkable decreases in RRD with SB in patients in their 20s-70s, in DR in their 60s, and in VH in their 60s and 70s. These findings did not change greatly when population changes were considered. All age groups from the 30 to 80s showed significant increases in the proportions of combined vitreoretinal and cataract surgery. CONCLUSION: The total number of cases of vitreoretinal surgery per fiscal year increased throughout the period. The increases in ERM and RRD with PPV and the decreases in DR and RRD with SB were remarkable.

Visual outcomes and prognostic factors of vitrectomy for lamellar macular holes and epiretinal membrane foveoschisis.

PURPOSE: To evaluate the visual outcomes of vitrectomy for lamellar macular hole (LMH) and epiretinal membrane (ERM) foveoschisis and to investigate the prognostic factor for postoperative visual acuity. METHODS: We retrospectively reviewed 15 LMH and 17 ERM foveoschisis eyes that had undergone a standard three-port pars plana vitrectomy with (12 eyes) or without (20 eyes) cataract surgery. Best-corrected visual acuity (BCVA) at postoperative three months and the final visit were compared to the preoperative measurements. We investigated the relationship between BCVA at the final visit and baseline parameters (age, preoperative BCVA, the presence of epiretinal proliferation [EP] and ellipsoid zone [EZ] disruption). The best explanatory variables for the final BCVA were investigated using the corrected Akaike information criterion (AICc) model selection. RESULTS: The mean age was 67.2 years. The mean follow-up duration was 30.7 months. Fifteen of 32 examined eyes were diagnosed as LMH and 17 eyes as ERM foveoschisis. Twelve eyes in LMH had EP and 13 eyes showed the disruption of EZ integrity. In total, BCVA significantly improved at 3 months postoperatively (p = 0.0013). A significant improvement was observed in ERM foveoschisis (p = 0.0085) but not in LMH group (p = 0.071). Comparing the BCVA between the baseline and the final visit, significant improvements were observed in total, ERM foveoschisis and LMH group (p<0.001, p<0.001 and p = 0.026, respectively). The optimal model for BCVA at the final visit included preoperative BCVA and the presence of EZ disruption (p<0.001 and p<0.001, respectively). CONCLUSION: Our results suggested that the final BCVA was dependent on preoperative BCVA and the presence of EZ disruption. Surgical indications might be warranted for LMHs with EZ disruption.

Frequency of hypotonic maculopathy observed by spectral domain optical coherence tomography in post glaucoma filtration surgery eyes.

PURPOSE: To report the frequency of post glaucoma filtration surgery hypotonic maculopathy determined by spectral domain optical coherence tomography (SD-OCT). METHODS: A cross-sectional retrospective observational study. Post glaucoma filtration surgery patients whose intraocular pressures (IOP) achieved 30% reduction from baseline or was controlled to IOP <14 mm Hg and had SD-OCT images and fundus photographs were enrolled. Hypotonic maculopathy was diagnosed independently on SD-OCT images and on fundus photographs. RESULTS: 112 eyes of 88 patients were included in this study. 17 eyes of 14 patients were diagnosed with hypotonic maculopathy on SD-OCT images (17/112, 15.2%). Among these eyes, only 3 eyes were also diagnosed with hypotony maculopathy on fundus photography. Hypotonic maculopathy on SD-OCT was found only in eyes with IOP ≤10 mm Hg. (17.4% in eyes with IOPs between 7 and 10 mm Hg, and 22.7% in eyes with IOP ≤ 6 mm Hg). Associations with age, sex, central corneal thickness, refractive error, IOP reduction rate and interval between surgery and OCT acquisition were not significant (P > 0.05). CONCLUSION: In most cases, hypotonic maculopathy detected by SD-OCT were not recognizable on fundus photographs. Hypotonic maculopathy was detected not only in eyes with conventional ocular hypotony (IOP < 6 mm Hg) but also in eyes with IOP between 7 and 10 mm Hg.

Development of a Spherical Model with a 3D Microchannel: An Application to Glaucoma Surgery.

Three-dimensional (3D) microfluidic channels, which simulate human tissues such as blood vessels, are useful in surgical simulator models for evaluating surgical devices and training novice surgeons. However, animal models and current artificial models do not sufficiently mimic the anatomical and mechanical properties of human tissues. Therefore, we established a novel fabrication method to fabricate an eye model for use as a surgical simulator. For the glaucoma surgery task, the eye model consists of a sclera with a clear cornea; a 3D microchannel with a width of 200-500 µm, representing the Schlemm's canal (SC); and a thin membrane with a thickness of 40-132 µm, representing the trabecular meshwork (TM). The sclera model with a clear cornea and SC was fabricated by 3D molding. Blow molding was used to fabricate the TM to cover the inner surface of the sclera part. Soft materials with controllable mechanical behaviors were used to fabricate the sclera and TM parts to mimic the mechanical properties of human tissues. Additionally, to simulate the surgery with constraints similar to those in a real operation, the eye model was installed on a skull platform. Therefore, in this paper, we propose an integration method for fabricating an eye model that has a 3D microchannel representing the SC and a membrane representing the TM, to develop a glaucoma model for training novice surgeons.

Autonomous Positioning of Eye Surgical Robot Using the Tool Shadow and Kalman Filtering.

Vitreoretinal surgery is one of the most difficult surgical operations, even for experienced surgeons. Thus, a master-slave eye surgical robot has been developed to assist the surgeon in safely performing vitreoretinal surgeries; however, in the master-slave control, the robotic positioning accuracy depends on the surgeon's coordination skills. This paper proposes a new method of autonomous robotic positioning using the shadow of the surgical instrument. First, the microscope image is segmented into three regions-namely, a micropipette, its shadow, and the eye ground-using a Gaussian mixture model (GMM). The tips of the micropipette and its shadow are then extracted from the contour lines of the segmented regions. The micropipette is then autonomously moved down to the simulated eye ground until the distance between the tips of micropipette and its shadow in the microscopic image reaches a predefined threshold. To handle possible occlusions, the tip of the shadow is estimated using a Kalman filter. Experiments to evaluate the robotic positioning accuracy in the vertical direction were performed. The results show that the autonomous positioning using the Kalman filter enhanced the accuracy of robotic positioning.

A surgical simulator for peeling the inner limiting membrane during wet conditions.

The present study was performed to establish a novel ocular surgery simulator for training in peeling of the inner limited membrane (ILM). This simulator included a next-generation artificial ILM with mechanical properties similar to the natural ILM that could be peeled underwater in the same manner as in actual surgery. An artificial eye consisting of a fundus and eyeball parts was fabricated. The artificial eye was installed in the eye surgery simulator. The fundus part was mounted in the eyeball, which consisted of an artificial sclera, retina, and ILM. To measure the thickness of the fabricated ILM on the artificial retina, we calculated the distance of the step height as the thickness of the artificial ILM. Two experienced ophthalmologists then assessed the fabricated ILM by sensory evaluation. The minimum thickness of the artificial ILM was 1.9 ± 0.3 µm (n = 3). We were able to perform the peeling task with the ILM in water. Based on the sensory evaluation, an ILM with a minimum thickness and 1000 degrees of polymerization was suitable for training. We installed the eye model on an ocular surgery simulator, which allowed for the performance of a sequence of operations similar to ILM peeling. In conclusion, we developed a novel ocular surgery simulator for ILM peeling. The artificial ILM was peeled underwater in the same manner as in an actual operation.