Testing a novel device for accurate ultrasound delivery during crystalline lens phacoemulsification surgery

Purpose: To assess whether the use of a patented, novel feedback device intended to accurately control phacoemulsification tip elongation is effective under varying machine settings and material resistance. Methods: Sculpt mode phaco (550-mm Hg Venturi pump; elongations, 35 and 70 μm) and quadrant settings (550-mm Hg Venturi pump; elongations, 15, 30, and 60 μm) were used in agar gel of incremental density (1%, 2%, 3%, and 6% in demineralized water). Dispersed lens fragments were also simulated with 6% agar gel spherules (2–5 mm in diameter; 550-mm Hg vacuum, and 60-μm elongation). Actual phaco tip elongation was measured on voltage readings from the piezoelectric crystals and compared to nominal elongation with feedback control off and on. Results: Mismatch between nominal and actual elongation when feedback control was off in sculpt mode varied between –13.51 μm and –23.07 μm of nominal elongation; in quadrant mode, mismatch varied between –2.79 μm and –20.41 μm. When the feedback control system was switched on, mismatch varied between –0.02 μm and +0.43 μm (P < 0.001 for all matchings). When the feedback system was off, the elongation mismatch among the 1%, 3%, and 6% agar was also statistically significant (P < 0.001). Elongation was 44.72 ± 4.16 μm with feedback control off and 60.02 ± 1.63 μm with it on (nominal elongation 60 μm; P < 0.001) when emulsifying agar 6% gel fragments. Dispersion of elongation data was also significantly wider when feedback control was turned off. Conclusions: A novel feedback control system effectively controls elongation accuracy regardless of the resistance offered by incremental agar gel concentrations. Translational Relevance: Implementing feedback control in phaco handpieces dramatically improves surgical accuracy. The translational value of this research relies on its immediate applicability to routine cataract surgery, resulting in a more appropriate use of ultrasound energy

Silicone Oil Tamponade Removal: Which Technique Is More Effective? An X-Ray Photoemission Spectroscopy Study

Purpose: To compare the efficacy of two surgical techniques used to remove silicone oil (SiO) emulsion tamponade after pars plana vitrectomy: triple air–fluid exchange (AFX) and balanced salt solution lavage (BSSL). Methods: X-ray photoemission spectroscopy measured silicon content of the dry residue of fluid samples taken during AFX and BSSL. Ten patients underwent AFX and five BSSL. Three fluid samples were taken per patient, and the dry residue of 10 drops per sample were analyzed. A fluid sample from a patient who never received SiO tamponade was also analyzed to set a “blank” reference sample. Results: Patients’ demographics showed no significant difference. Sample 1 of the two groups contained comparable silicon content while samples 2 and 3 of the AFX group contained significantly more silicon than that of the BSSL group (15.0 ± 0.1 and 12.0 ± 0.9 for the AFX group vs. 10.7 ± 1.4 and 5.2 ± 0.6 for the BSSL group, respectively; P < 0.05). The cumulative amount of silicon in the three successive samples was also significantly higher for the AFX group (42.3 ± 1.6 vs. 32 ± 2; P < 0.0001). The average silicon content ratio of consecutive samples was significantly higher for the AFX group compared to the BSSL group (0.90 ± 0.01 vs. 0.58 ± 0.06; P = 0.006). Conclusions: Triple AFX removed more silicon than triple lavage. The eye wall actively interacts with silicon emulsion retaining silicon content rather than behaving as a neutral container. Translational Relevance: Triple air–fluid exchange removed more silicon than BSS lavage. Neither technique behaved as a well-mixed box dilution, suggesting the eye walls actively retain emulsion and a dynamic equilibrium is established between silicon dispersion and the eye wall surface

Human Vitreous Collagen Fragments Dimension As a Function of Vitrectomy Cut Rate

Purpose: To study the dimensions and distribution of human vitreous collagen type II fragments collected after vitrectomy performed at varying cut rates and to evaluate if increasing the cut rate produces smaller collagen fragments, thus reducing retinal traction and/or viscosity. Methods: Fluid was collected during core vitrectomies performed for macular surgery at cut rates from 1000 to 16,000 cuts per minute (CPM) and immediately refrigerated. Protein fractions were separated by molecular weight (MW; >100 kDa, 50–100 kDa, 50– 30 kDa, 30–10 kDa, and <10 kDa) through centrifugal filters. The Human Collagen II ELISA Kit colorimetric assay was then used to measure the COL2A1 in unfiltered and filtered samples. Results: Vitreous samples collected after vitrectomy performed at 16,000 CPM contained a higher concentration of protein with MW over 100 kDa than at any other cutting frequency (P < 0.01). No significant differences were found in fractions collected with a MW between 50 and 100 kDa. Collagen type II fragments over 100 kDa were significantly more represented than smaller fragments at each cut rate. The proportion of smaller (50–100 kDa) collagen fragments compared with those over 100 kDa was higher at 2000 CPM than at higher cut rates. Conclusions: Vitreous samples collected at different cut rates do not contain a significantly different proportion of collagen type II fragments of the tested MW. The extreme variability of vitreous flowthrough the cutter port may explain the uncertain predictability of collagen fragment MWs. Translational Relevance: Increasing the cut rate does not produce vitreous fragments of proportionally smaller dimension. It is necessary to achieve an invariant instantaneous flow through the cutter port in order to decrease retinal traction during vitrectomy

Hydraulic resistance of vitreous cutters: The impact of blade design and cut rate

Purpose: To measure the hydraulic resistance (HR) of vitreous cutters equipped with a Regular guillotine Blade (RB) or double edge blade (DEB) at cut rates comprised between 0 and 12,000 cuts per minute (CPM) and compare it with vitreous fragment size. This was an in vitro experimental study; in vivo HR measure and vitreous sampling. Methods: HR, defined as aspiration pressure/flow rate, was measured in balanced salt solution (BSS; Alcon, Fort Worth, TX) (in vitro) and during pars plana vitrectomy of 20 consecutive patients aged 18 to 65, undergoing macular surgery. HR was recorded at increasing cut rates (500-6000 CPM for the RB and 500-12,000 CPM for the DEB; 5 mL/ min flow). Vitreous samples were withdrawn and analyzed with Western and collagen type II and IX immunostaining to evaluate protein size. The main outcome measures were hydraulic resistance (mm Hg/ml/min [±SD]) and optic density for Western blot and immunostaining. Results: RB and DEB showed identical HR in BSS between 0 and 3000 CPM. Above 3000 CPM, RB HR steadily increased, and was significantly higher than DEB HR. Vitreous HR was also similar for the two blades between 0 and 1500 CPM. Above1500 CPM, RB offered a significantly higher resistance. Western blot and immunostaining of vitreous samples did not yield a significant difference in size, regardless of blade type and cut rate. Conclusions: DEB is more efficient, offering a lower HR than RB over 1500 CPM in human vitreous. There is no viscosity reduction as a function of cut-rate between 1500 and 12,000 CPM, as HR does not vary. Translational Relevance: Future vitreous cutters will benefit of a DEB; optimal cut rate needs to be defined, and the simple increase of cut rate does not provide benefits after a certain limit to be assessed

Phacoemulsification Tip Elongation Under Standardized Resistance: An Objective Measure of Human Crystalline Lens Hardness

Purpose: To establish a correlation between phacoemulsification tip normalized driving voltage (NDV) and crystalline lens hardness and use it as an objective measure of lens hardness. The study used a phaco tip equipped with previously validated elongation control adjusting the driving voltage (DV) to produce invariant elongation regardless of resistance. Methods: The laboratory study measured the mean and maximum DV of the phaco tip immersed in glycerol–balanced salt solution and correlated the DV with the kinematic viscosity at 25, 50, and 75 μm tip elongation. The NDV were obtained by dividing the DV in glycerol by the DV in the balanced salt solution. The clinical arm of the study recorded DV of 20 consecutive cataract surgeries. The correlation of mean and maximum NDV to Lens Opacities Classification System (LOCS) III classification, patient’s age and effective phaco time were evaluated. Results: The mean and maximum NDV correlated with the kinematic viscosity of the glycerol solution (P < 0.001 in all cases). Mean and maximum NDV during cataract surgery correlated with patients’ age, effective phaco time, LOCS III nuclear color, and nuclear opalescence (P < 0.001 in all cases). Conclusions: When a feedback algorithm is running, DV variation strictly correlates with encountered resistance in glycerol solutions and real-life surgery. NDV significantly correlates with the LOCS classification. Future developments might include sensing tips that react to lens hardness in real time. Translational Relevance: The study correlates for the first time phaco tip DV and crystalline lens mechanical properties, establishing an objective and reliable measure of lens hardness. This may lead to smart phaco tips reacting to cataract hardness change in real time and sparing ultrasound dispersion

Hypotensive effect of pilocarpine after argon laser trabeculoplasty

The exact mechanism of action of argon laser trabeculoplasty (ALT) has only been presumptively proposed. There are two hypotheses of action of ALT: the first is the mechanical theory and the second is centered on the possibility of laser-induced modifications of trabecular cells. The goal of our investigation was to verify if pilocarpine determines a decrease of intraocular pressure mainly by a mechanical stretching of the meshwork; if pilocarpine could lower intraocular pressure after ALT; and thus if the mechanism of action of laser treatment could mainly be attributable to a mechanical strain of the trabecular meshwork. Twenty-one patients affected with primary open angle glaucoma had been recruited for the study. Twenty-one eyes underwent trabeculoplasty. All the patients were followed for 6 months. Statistical analysis of the data revealed that pilocarpine was not able to induce a further decrease of intraocular pressure after trabeculoplasty. Moreover, the maximum decrease of intraocular pressure induced by pilocarpine before laser treatment was not statistically different from the tensional values after ALT. The results of the present investigation suggest that the mechanism of action of trabeculoplasty is probably attributable to a mechanical stretching of the trabecular meshwork and the results show the inefficacy of pilocarpine after laser treatment in the management of glaucomatous patients

Hypotensive effect of pilocarpine after argon laser trabeculoplasty

The exact mechanism of action of argon laser trabeculoplasty (ALT) has only been presumptively proposed. There are two hypotheses of action of ALT: the first is the mechanical theory and the second is centered on the possibility of laser-induced modifications of trabecular cells. The goal of our investigation was to verify if pilocarpine determines a decrease of intraocular pressure mainly by a mechanical stretching of the meshwork; if pilocarpine could lower intraocular pressure after ALT; and thus if the mechanism of action of laser treatment could mainly be attributable to a mechanical strain of the trabecular meshwork. Twenty-one patients affected with primary open angle glaucoma had been recruited for the study. Twenty-one eyes underwent trabeculoplasty. All the patients were followed for 6 months. Statistical analysis of the data revealed that pilocarpine was not able to induce a further decrease of intraocular pressure after trabeculoplasty. Moreover, the maximum decrease of intraocular pressure induced by pilocarpine before laser treatment was not statistically different from the tensional values after ALT. The results of the present investigation suggest that the mechanism of action of trabeculoplasty is probably attributable to a mechanical stretching of the trabecular meshwork and the results show the inefficacy of pilocarpine after laser treatment in the management of glaucomatous patients

Computational fluid dynamics of intraocular silicone oil tamponade

Purpose: To investigate the behavior of silicone oil (SiO) at the steady equilibrium and during saccades and calculate SiO-retina contact, shear stress (SS), and shear rate (SR). Methods: A 24mmphakic eye mesh model underwent 50°/0.137s saccade. The vitreous chamber compartment was divided into superior and inferior 180° sectors: Lens, preequator, postequator, and macula. SiO-retina contact was evaluated as a function of fill percentages between 80% and 90% for a standing patient, 45° upward gaze, and supine. SS and SR for 1000mPa-s (SiO1000) and 5000mPa-s (SiO5000) silicon oilwere calculated. Results: SiO fill between 80% to 90% allowed 55% to 78% retinal contact. The superior retina always kept better contact with SiO, regardless of the fill percentage (P < 0.01). SiO interface thoroughly contacted the macula only in standing position. SS followed a bimodal behavior and was always significantly higher for SiO5000 compared to SiO1000 (P < 0.01) throughout the saccade. The macula suffered the highest mean SS in standing position, while throughout the saccade the average SS was maximum at the SiO-aqueous interface. SR was significantly higher for SiO1000 compared to SiO5000 (P < 0.001). Conclusions: SS on the retinal surface may instantaneously exceed reported retinal adhesiveness values especially at the SiO-aqueous interface and possibly favor redetachment. Despite 90% SiO fill the inferior retina remains extremely difficult to tamponade. Translational Relevance: Accurate assessment of retina-tamponade interaction may explain recurrent inferior retinal redetachment, silicone oil emulsification, and help to develop better vitreous substitutes