Mario Iossa

The Pathogenesis of Retinal Damage in Blunt Eye Trauma: Finite Element Modeling

PURPOSE To test the hypothesis that blunt trauma shockwave propagation may cause macular and peripheral retinal lesions, regardless of the presence of vitreous. The study was prompted by the observation of macular hole after an inadvertent BB shot in a previously vitrectomized eye. METHODS The computational model was generated from generic eye geometry. Numeric simulations were performed with explicit finite element code. Simple constitutive modeling for soft tissues was used, and model parameters were calibrated on available experimental data by means of a reverse-engineering approach. Pressure, strain, and strain rates were calculated in vitreous- and aqueous-filled eyes. The paired t-test was used for statistical analysis with a 0.05 significance level. RESULTS Pressure at the retinal surface ranged between -1 and +1.8 MPa at the macula. Vitreous-filled eyes showed significantly lower pressures at the macula during the compression phase (P < 0.0001) and at the vitreous base during the rebound phase (P = 0.04). Multiaxial strain reached 20% and 25% at the macula and vitreous base, whereas the strain rate reached 40,000 and 50,000 seconds(-1), respectively. Both strain and strain rates at the macula, vitreous base, and equator reached lower values in the vitreous- compared with the aqueous-filled eyes (P < 0.001). Calculated pressures, strain, and strain rate levels were several orders of magnitude higher than the retina tensile strength and load-carrying capability reported in the literature. CONCLUSIONS Vitreous traction may not be responsible for blunt trauma-associated retinal lesions and can actually damp shockwaves significantly. Negative pressures associated with multiaxial strain and high strain rates can tear and detach the retina. Differential retinal elasticity may explain the higher tendency toward tearing the macula and vitreous base.

Primary blast injury to the eye and orbit: finite element modeling

PURPOSE Primary blast injury (PBI) mostly affects air-filled organs, although it is sporadically reported in fluid-filled organs, including the eye. The purpose of the present paper is to explain orbit blast injury mechanisms through finite element modeling (FEM). METHODS FEM meshes of the eye, orbit, and skull were generated. Pressure, strain, and strain rates were calculated at the cornea, vitreous base, equator, macula, and orbit apex for pressures known to cause tympanic rupture, lung damage, and 50% chance of mortality. RESULTS Pressures within the orbit ranged between +0.25 and -1.4 MegaPascal (MPa) for tympanic rupture, +3 and -1 MPa for lung damage, and +20 and -6 MPa for 50% mortality. Higher trinitrotoluene (TNT) quantity and closer explosion caused significantly higher pressures, and the impact angle significantly influenced pressure at all locations. Pressure waves reflected and amplified to create steady waves resonating within the orbit. Strain reached 20% along multiple axes, and strain rates exceeded 30,000 s(-1) at all locations even for the smallest amount of TNT. CONCLUSIONS The orbits pyramidlike shape with bony walls and the mechanical impedance mismatch between fluidlike content and anterior air-tissue interface determine pressure wave reflection and amplification. The resulting steady wave resonates within the orbit and can explain both macular holes and optic nerve damage after ocular PBI.

Ultrasound imaging velocimetry of the human vitreous

Knowledge of vitreous motion in response to saccades is a prerequisite for understanding vitreous rheology. Purpose of present paper is to introduce Ultrasound Image Velocimetry of the human eye, measure scleral and vitreous velocity fields and test the reproducibility of the proposed technique. Twelve patients with varying diagnosis underwent Ocular Dynamic Ultrasound; scleral angular velocity (V(S)) was measured by 2 different operators and reproducibility calculated. Squared velocity of the vitreous (E), which is representative of kinetic energy per unit mass, was computed from velocity. The time evolution of the energy of the vitreous was described by its spatial average (E(S)), whereas spatial distribution was described by its time average (E(T)). Peak and average E(S), the ratio K(p) of the peak of the spatially averaged kinetic energy per unit mass to the maximum squared scleral angular velocity, vitreous motion onset time (T(O)) and vitreous motion decay time (T(D)) were also defined. Inter-operator reproducibility coefficient was 0.043 and correlation between operators was significant. V(S), peak and average E(S), K(p) ratio and T(D) differed among patients but not among operators. V(S) correlated with E(S) and T(D). E(S) and T(D) but not V(S), were significantly different in patients with Posterior Vitreous Detachment. Patients with retinal detachment showed significantly higher V(S) and E(S). K(p) was inversely correlated to age and refraction. Measures proved accurate and reproducible. E is related to V(S), retinal traction and mechanical stimulation. Identified variables varied with age, refraction pathologic conditions.

Effect of light on oxygen-induced retinopathy in the rat model

The purpose of this study was to establish whether exposure to intense lighting favors the development or aggravates experimental oxygen-induced retinopathy in the new-born rat. Five groups of Wistar rats were studied. The control group was maintained for the first 14 days of life under conditions of cyclical (12L∶12D) lighting at 12 Lx in room air. Two other groups were subjected, for the same amount of time, to semi-darkness (2 Lx; 12L∶12D), one with room air and the other with supplemental 80% oxygen. The final two groups were exposed to the same room air and hyperoxic treatments under intense lighting conditions (600 Lx; 12L∶12D).After the treatment period, four rats were randomly chosen from each group, sacrificed and their retinas examined under electron microscope. Marked structural changes were seen only in the photoreceptor outer segments of those rats exposed to intense light.In eighty-five of the remaining rats retinal vascular morphology was examined in retinal flat mounts after intracardiac injection of India ink. Retinopathy was observed in rats treated with hyperoxia but no significant differences could be attributed to the light conditions under which the retinopathic rats had been maintained.In the rest of the rats, axonal transport along the optical pathways was evaluated after intravitreal injection of (3H) taurine. In the two groups exposed to hyperoxia, axonal transport was altered, but less markedly in those exposed to intense lighting than in those exposed to semi-darnkess. Intense illumination under conditions of normoxia favors axonal transport. Exposure to intense lighting does not seem to aggravate oxygen induced retinopathy in the rat though it does produce structural lesions of the photoreceptors.

Fluid dynamics of vitrectomy probes

Purpose: To characterize the fluidics of vitreous cutter port in response to aspiration and blade motion using particle image velocimetry techniques. Diverse surgical scenarios and fluid characteristics were replicated. Methods: The 23-gauge vitreous cutters were immersed in seeded Balanced Salt Solution (BSS) (Alcon, Forth Worth, TX) or egg albumen, and high-speed video was recorded. Fluid velocity, kinetic energy (KE), and acceleration generated by Venturi and peristaltic pumps were measured in aspiration only (200 and 300 mmHg), low-speed vitrectomy (1,600 cuts per minute; 200 mmHg vacuum), and high-speed vitrectomy (3,000 cuts per minute; 300 mmHg vacuum) modes. Results: The Venturi pump generated significantly higher KE than peristaltic pump in BSS (P < 0.0001 for each pair), and aspiration only yielded significantly higher KE. Cutting activation generated significant acceleration (P < 0.001), and the peristaltic pump produced higher positive and negative acceleration peaks (P < 0.001) than the Venturi pump. In egg albumen, the peristaltic pump generated significantly more KE than the Venturi pump (P < 0.001) and perturbed a much wider area. Acceleration was higher for the peristaltic pump in low-speed mode (P < 0.001), whereas in high-speed modality, the Venturi pump produced the highest acceleration peaks (P < 0.001). Conclusion: Pump type and blade motion largely influence velocity, KE, and acceleration. In BSS, the Venturi pump induces higher KE and acceleration, although perturbing fluid less diffusely. In egg albumen, the peristaltic pump perturbed a much wider area and induced a higher KE and acceleration than the Venturi pump, even more so at lower cut rates. As a conclusion, particle image velocimetry allowed precise characterization of fluid velocity in response to cutter activation, suggesting a pragmatic approach to surgical scenarios.

A new vitreous cutter blade engineered for constant flow vitrectomy.

The standard guillotine-shaped vitreous cutter blade (hereafter named Regular Blade [RB]) did not substantially change over the past 40 years, because of its simple and robust design. The asynchronous suction and cutting action, typical of RB blades, determines complete port obstruction generating flow instability and fluid acceleration that results in limited efficiency and eventually retinal traction. Newer blade shapes allowing residual flow when the port is “closed,” have been recently described and shown to yield a more favorable duty cycle, fluid dynamics, and volumetric flow rate. We herein introduce a further improvement of blade design, named Constant Flow Blade (CFB; Twedge Cutter Blade; Optikon 2000 Inc, Rome, Italy), that maintains the amount of open port surface invariant throughout the duty cycle, achieving a much higher flow while doubling cut rate. Description

Triaging and coding ophthalmic emergency -The Rome Eye Scoring System for Urgency and Emergency (RESCUE) : A pilot study of 1000 eye-dedicated emergency room patients

Purpose. Ophthalmic emergency (OE) triage is essential for prompt recognition of urgent cases. To date, no formal eye-dedicated triaging system has been widely accepted. The purpose of the present study is to propose a fast, accurate, and reproducible coding scale called the Rome Eye System for Scoring Urgency and Emergency (Rescue). Methods. Phase 1 of the study is a retrospective analysis of electronic medical records (EMR); phase 2 is a prospective consecutive series. Phase 1 included 160,936 patients. Phase 2 included 1000 consecutive patients referred to the emergency department (ED) of our institution. In phase 1, the authors retrospectively analyzed EMRs of patients presenting to the ED, listing signs and symptoms most frequently associated with hospitalization. Redness, pain, loss of vision, and the risk for an open eye were identified and assigned a score ranging from 0 to 12. Color coding was assigned based on increasing scoring: 0–3 white, 4–7 green, 8–12 yellow code. In phase 2, 1000 consecutive ED patients were enrolled and prospectively coded according to RESCUE. After diagnosis and proper treatment, EMRs were retrospectively reviewed by a masked physician and patients recoded (Retro coding) according to clinical course. Correlation between Rescue and Retro coding was calculated. Main outcome measures: Prospective and retrospective ED color coding correlation. Results. A total of 160,936 EMR were retrospectively analyzed; 2407 (1.4%) patients required hospitalization. Loss of vision (90%), redness (76%), and pain (47%) were the most frequent complaints. Rescue significantly correlated to Retro coding (p<0.01): 841/1000 patients coded exactly the same color, 45/1000 were overestimated by one color class, none by two, 107/1000 underestimated by one, and 6/1000 by two classes. The 32/1000 hospitalized patients in the prospective cohort had a Rescue score significantly higher than non-admitted patients (p<0.01) and color coding among admitted and dismissed patients was significantly different as well (p<0.01). Conclusions. The Rescue system seems promising in terms of usefulness and ease of implementation. The high correlation between Rescue code assigned prospectively and the post-diagnosis coding, as well as the prompt discrimination of cases that eventually required hospitalization, may lead to a wider use of the Rescue system. Further testing on larger samples and different institutions is warranted.

Oxygen-induced retinopathy in newborn rats: Orthograde axonal transport changes in optic pathways

The aim of this study was to evaluate axonal transport along the optic pathways of neonatal rats in which oxygen-induced retinopathy had been experimentally produced. One group of 116 rats was exposed to an FiO2 of 80% for the first 5 days of life and then kept under room-air conditions for the following 10 days. A second group of 108 rats was maintained under room-air conditions for the first 15 days of life. On the 16th day of life, 1.5 microliter of [35S]taurine was injected into the vitreous of the right eye of each animal and radioactivity was measured, at various intervals from the injection, in the right optic nerve, the chiasma and the left optic tract. Statistically significant reductions in axonal transport were observed in all three segments of the optic pathways of the oxygen-supplemented animals compared with the control group. The authors discuss various explanations for their findings and hypothesize that the alterations observed in this study may have significant and more or less long-term effects on the normal maturation of the visual system.

Ocular perfusion pressure during pars plana vitrectomy: a pilot study.

PURPOSE Unexplained visual field loss after pars plana vitrectomy (PPV) has been reported in up to 14% of all uncomplicated cases with signs varying from visual field defect and disc pallor, to optic atrophy, loss of vision, and phthisis bulbi. Among the postulated pathogenic mechanism is ocular hypoperfusion due to insufficient blood pressure (NBP) and/or elevated IOP, or to their mismatch. The purpose of this study is to assess if, to what extent, and for how long the intraoperative simultaneous variation of IOP and NBP causes mean ocular perfusion pressure (MOPP) to drop below values considered safe, during PPV. METHODS An IOP sensor placed in the infusion cannula recorded 6 readings per second, while arm systolic and diastolic NBP were taken every 5 minutes throughout surgery and deemed stable in between readings. Supine MOPP was calculated as (115/130) mean arterial pressure--IOP. Surgical monitor video overlay displayed all data in real time and saved them for analysis. RESULTS Average IOP significantly increased during surgery, while NBP decreased, compared to baseline. As a result, intraoperative MOPP decreased an average 37.1% compared to baseline (range, 13.8%-58.6%; P < 0.05). Of 18 patients, 16 (88.8%) had a significant intraoperative MOPP decrease; 15/18 (83.3%) spent more than 20%, and 5/18 (27.7%) more than 50% of the entire surgery below 30 mm Hg MOPP. Surgical maneuvers, such as phacoemulsification, silicone oil removal, and fluid injection, were associated with significant MOPP decrease, while peeling and vitrectomy were not. CONCLUSIONS The MOPP may decrease significantly in course of PPV, acutely and for longer time. Surgical maneuvers, including silicone oil removal and combined phacoemulsification, pose a higher risk for MOPP reduction. Discretion should be exercised while administering deep sedation, since it may further lower MOPP through undue blood pressure reduction.

Choroidal hemorrhage drainage through 23-gauge vitrectomy cannulas.

Choroidal Hemorrhage Drainage Through 23-Gauge Vitrectomy Cannulas Choroidal effusion syndrome (CES) and suprachoroidal hemorrhage (SCH) are rare but dreaded complications of virtually every intraocular procedure,1 including cataract, glaucoma surgery, penetrating keratoplasty, scleral buckles, and vitrectomy.2 They may also spontaneously arise in hypertensive and/or vasculopathic patients.3 Treatment of CES and SCH is still largely debated and includes a more conservative pharmacologic approach and surgical drainage occasionally combined with pars plana vitrectomy (PPV) and tamponade.4 Small-gauge transconjunctival PPV was introduced in 20025 as a niche surgical technique devoted to “minimal surgery,” mostly macular puckers, macular holes, diagnostic vitrectomy, and other minor vitreal procedures.6 Ever since, small-gauge transconjunctival PPV indications have greatly expanded because of armamentarium refinement and surgical skill improvement. Today, small-gauge transconjunctival PPV encompasses the entire spectrum of vitreous surgery, from diabetic retinopathy to proliferative vitreoretinopathy and trauma cases.7 The purpose of this article was to report the cases of 3 consecutive patients with CES and/or SCH surgically drained by means of 23-gauge (23G) vitrectomy cannulas combined with 23G PPV and silicone oil (SiO) tamponade.