AXIAL ROTATION VITRECTOMY: Back to the Future? the Fluidics of a Prototype Vitreous Cutter Probe.

PURPOSE: To characterize the fluidics of axial rotating vitreous cutter probe (RT) compared with the standard guillotine (regular blade), when tested in Balanced Salt Solution (Alcon Laboratories, Forth Worth, TX). METHODS: RT and regular blade (RB) cutter probes connected to the same vitrectomy console used a peristaltic pump. The authors measured instantaneous flow through aspiration tubing proximal to the handpiece, fluid velocity, and acceleration at the port by means of particle image velocimetry. RESULTS: Average flow at aspiration tubing of RT and RB did not vary significantly. Regular blade probes produced higher instantaneous flow fluctuation than RT at any considered cut rate (RB 1,600 6.4 ± 5.3 mL/minute; RB 3,000 11.8 ± 6.3 mL/minute; RT 1,600 0.9 ± 0.7 mL/minute, and RT 3,000 1.8 ± 0.8 mL/minute, respectively. P < 0.001 in all cases). Regular blade also yield significantly higher fluid velocity at cutter port compared with RT (RB 1,600 85.8 ± 70.1 mm/second; RB 3,000 81.6 ± 66.4 mm/second; RT 1,600 71.9 ± 40.3 mm/second; and RT 3,000 32.9 ± 20.8 mm/second. P < 0.001 in all cases). Fluid acceleration at the cutter port was higher when the RB was used (RB 1,600 26.85 ± 30.18 mm/second; RB 3,000 33.76 ± 34.09 mm/second; RT 1,600 24.01 ± 21.94 mm/second; and RT 3,000 16.62 ± 17.87 mm/second. P < 0.001 in all cases). CONCLUSION: RT blade design causes less instantaneous flow fluctuation within the aspiration tubing, and also lower fluid velocity and lower acceleration at the cutter port. Fluidics suggests a safer cutting action and a reduced risk of retinal incarceration.

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.

Introducing new vitreous cutter blade shapes: a fluid dynamics study.

PURPOSE: To assess the efficacy of novel vitreous cutter blades compared with the regular guillotine by means of particle image velocimetry. Tested blades included a regular blade (RB) and newer designs where a circular (hole blade [HB]) or a slit aperture (slit blade [SB]) had been opened proximal to the cutting edge. METHODS: Twenty-three-gauge probes were immersed in BSS or egg albumen, and high-speed video (1,000 frames per second) was recorded. Duty cycle, flow rate, and acceleration generated by Venturi and peristaltic pumps were measured under cutter settings simulating "low-speed" vitrectomy (1600 cuts per minute, 200 mmHg vacuum) and "high speed" vitrectomy (3000 cuts per minute, 300 mmHg vacuum). RESULTS: The SB and HB had a significantly more favorable duty cycle than that of the RB (P < 0.01) and higher BSS flow rate regardless of the aspiration. The SB flow rate in albumen was significantly higher than that of the HB and RB only over 1,000 cuts per minute using a peristaltic pump and at any cut rate with Venturi pump (P < 0.001). The SB also yielded the lowest fluid acceleration than both the HB and SB (P < 0.001 in all cases). CONCLUSION: The HB and SB proved to be significantly more efficient than the RB, with better duty cycle and higher flow rate. The SB generated significantly less fluid acceleration than any other tested blade, regardless of the fluid viscosity and pump technology. The SB design is significantly more efficient and possibly safer than both HB and RB.

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.

Combined pars plana vitrectomy and artificial iris diaphragm implant after globe rupture.

BACKGROUND: Retinal detachment (RD) associated with aniridia due to globe rupture (GR) is an uncommon condition with a severe prognosis. Surgical technique must address anterior and posterior segment issues secondary to the altered compartmentalization and increased risk for corneal toxicity. The purpose of this paper is to report a series of GR patients undergoing combined pars plana vitrectomy (PPV) and artificial iris diaphragm (AID) implant for the repair of RD associated to aniridia. METHODS: The authors retrospectively reviewed 12 consecutive patients operated on by a single surgeon. Surgery consisted of a standard three-port PPV with extensive bimanual dissection of vitreous base and ciliary body membrane and combined AID implant. Office visits included Snellen visual acuity (VA), intraocular pressure measurement, biomicroscopy and indirect ophthalmoscopy. AID prosthesis included aniridic IOLs, Heimann's PMMA and silicone diaphragm. RESULTS: Mean age was 53 years and mean follow-up was 19 months. At the end of follow-up, seven patients gained more than two lines (58.3%), two lost their vision (16.6%) and three were unchanged (25%). Seven patients (58.3%) had a VA better than 20/400 and one (8%) 20/40 vision. Eight patients (66.6%) retained a clear cornea, two (16.6%) had minimal corneal oedema and two (16.6%) corneal decompensation. Implanted prosthesis included two silicone diaphragms, four PMMA diaphragms and six aniridic IOLs. After an average 1.6 operations, the retina was completely attached in six patients (50%), partially attached in four (33.3%) and detached in two (16.6%). CONCLUSION: RD associated to GR carries a guarded prognosis both due to RD complexity and hypotony. The combined repair of RD and aniridia after GR offers the advantage of addressing all issues at one time allowing correct eye compartmentalization and better tamponade effect. Successful anatomical and functional results can be achieved although multiple surgeries are often needed.

Scleral buckle removal associated with pars plana vitrectomy for recurrent retinal detachment.

PURPOSE: Scleral buckle (SB) removal is rarely performed due to extrusion, infection, or diplopia. We report a series of patients with recurrent retinal detachment (RRD) after primary SB due to new breaks occurring at sites where the presence of a pre-existing SB was judged counterproductive. All patients were treated by means of pars plana vitrectomy (PPV) and SB removal with the sole purpose of achieving a more favorable retinal profile. METHODS: We retrospectively reviewed all patients undergoing PPV and SB removal for RRD due to new breaks occurring at sites hidden by pre-existing exoplants. RESULTS: Mean age was 52 years and VA on presentation was 20/620 and 20/216 at latest visit (p<0.01), 23 months of follow-up. On presentation, 3/11 (27%) had a VA better than 20/400 and 1/11 (9%) better than 20/40. At the end of follow-up, 9/11 (81%) and 3/11 (27%) saw better than 20/400 and 20/40 (p<0.05). At the end of follow-up, 8/11 (72%) had an attached retina, 2/11 (18%) had a partially attached retina, and 1/11 (9%) had a total RD. Explanted buckles included 5 silicone sponges and 6 solid silicone rubber elements. CONCLUSIONS: Although occasionally cumbersome and time-consuming, SB removal may provide a more favorable retinal profile and improve retina-tamponade contact. Larger series are needed to assess if this translates into a significant benefit in the treatment of selected RRD.

Instantaneous flow rate of vitreous cutter probes.

PURPOSE: We report on instantaneous volumetric flow rate of vitreous cutters measured by means of particle image velocimetry (PIV). METHODS: In an in vitro experimental study, vitreous cutters mounting a regular blade (RB) or modified Twedge blade (TB) engineered for higher flow were connected to a console machine equipped with a double peristaltic and Venturi pump, and immersed in balanced salt solution (BSS). Instantaneous flow was measured on aspiration tubing sections proximal to the cutter hand piece. Measures settings were as follows: (1) regular functioning at 3000 and 6000 cuts per minute (cpm) with 300 mm Hg aspiration with both pumps, (2) aspiration tubing clamped proximal to pump cassette, and (3) aspiration tubing clamped proximal to hand piece, and (4) flow fluctuation as a function of cut rate also was calculated. For main outcome measures, instantaneous volumetric flow rate in mL/min and flow fluctuation measured as the standard deviation of flow rate were measured. RESULTS: Regular functioning shows sinusoidal flow oscillating at cut rate frequency, with amplitude between ±50 mL/min at 3000 cpm and ±35 mL/min at 6000 cpm. The TB always determined a bimodal wave and neither blade nor pump type influenced the sinusoidal pattern of flow. Clamping aspiration tubing zeroes flow, but does not influence fluctuation frequency or amplitude. Clamping at the hand piece determined a significantly higher oscillation. Oscillation amplitude retain a typical resonance pattern with significant changes in function of cut rate and resonance occurs at approximately 4000 cpm. CONCLUSIONS: Cutter blade action determines instantaneous flow rate fluctuation that interferes significantly with cutter suction and hampers a steady suction through cutter port. In a surgical scenario, this translates into a higher risk of inadvertent retinal entrapment and lower predictability of cutter behavior, especially at frequency approaching resonance.

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.

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 orbit's 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.

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.

Intracoital subfoveal hemorrhage after tadalafil (cialis) premedication: a case report.

PURPOSE: The purpose of this study is to report the first case, to our knowledge, of intracoital subfoveal hemorrhage occurring 1 hour after tadalafil premedication in a patient with previously undiagnosed retinal angiomatous proliferation and erectile dysfunction. METHODS: This is an interventional case report. The patient underwent Snellen vision acuity measurement, anterior and posterior segment biomicroscopy, and indirect ophthalmoscopy. Optical coherence tomography, fluorescein angiography, and indocyanine green angiography were also performed as needed. Recombinant tissue plasminogen activator 100 µg/0.1 mL and 0.3 mL pure SF6 gas were injected in the vitreous on presentation. Four days later, the patient received 1.25 mg/0.1 mL of intravitreal bevacizumab. RESULTS: One day after recombinant tissue plasminogen activator and gas injection, visual acuity rose to 20/60-2. A week later, visual acuity was unchanged, and the subretinal hemorrhage displaced from the foveola. Optical coherence tomography showed a marked regression of submacular thickening. CONCLUSION: Despite strict time correlation, the submacular hemorrhage cannot be unequivocally attributed to tadalafil assumption because many other risk factors are to be considered: the Valsalva maneuver above all. Nonetheless, a suspicion should be raised, at least as a cofactor, given the drug mechanism of action and the report of vascular abnormalities bleeding in the literature, including cerebral arterovenous malformation and epistaxis. Caution should be exercised in the prescription of phosphodiesterase type 5 inhibitors to patients with known vascular abnormalities including retinal and choroidal abnormalities: retinal angiomatous proliferation, classic and occult neovascularization of any origin, and also, possibly, hemangioma.

Intraocular cilium masquerading as a parasite.

BACKGROUND: Among the many different intraocular foreign bodies (IOFBs), eyelashes represent an uncommon finding almost invariably associated with a history of penetrating trauma. The authors describe a woman who had no signs and denied any history of trauma with an odd-looking, whitish, worm-like IOFB eventually identified by pathologic analysis as a cilium. CASE REPORT: A 58-year-old lady complaining of floaters with mild loss of vision and redness presented to our institution. Slit-lamp examination revealed trace cells, while the fundus showed 1+ vitreous cells and the presence of a 3- to 4-mm-long, 0.3-mm-wide bright white "fluffy" wormlike object in the anterior vitreous. Medical history was unremarkable. The patient underwent pars plana vitrectomy with IOFB removal, and the specimen was sent for pathologic analysis that revealed the presence of a cilium encased in collagen fibers and mature adipose tissue. Vitreous cultures did not yield any pathogen. DISCUSSION: Eyelashes as IOFBs have been described in several reports and are invariably associated with penetrating trauma. Intraocular cilia with no apparent history of trauma have been rarely reported. Our patient had a very peculiar presentation because of the "fluffy" bright white "capsule" that although readily visible resembled a parasite more than a cilium. The presence of adipose tissue at the base of the cilium that may have been dragged with the eyelash at the time of penetration is also a matter of speculation.