Numerical simulation of the fluid dynamics in vitreous cavity due to saccadic eye movement.

In this study, the flow dynamics of vitreous due to saccadic movements following vitreous liquefaction or in post-vitrectomy eyes is investigated. Using a dynamic mesh technique, the eye motion was modeled and unsteady three-dimensional forms of continuity and Navier-Stokes equations were solved numerically. Firstly, the numerical model was validated for a sphere as a model of vitreous chamber and agrees well with the results based on available analytic solutions and experimental data. Then, numerical simulation was performed based on a deformed sphere with an indentation representing the lens. This consists of a vitreous cavity filled with a liquid having the viscosity of liquefied vitreous and balanced salt solution. The wall shear stress on the retina was computed and compared for various saccade amplitudes. Also, the effect of variation in vitreous viscosity and the size of lens indentation are investigated. The results show that the secondary flow in the vertical direction in the vitreous cavity is much higher for the liquefied vitreous and balanced salt solution compared with that for silicone oil. The possible effect of shear stress on the retinal detachment for all studied cases is discussed. A semi-analytic correlation is also developed for maximum wall shear stress of the spherical domain that is subjected to sinusoidal rotations.

Supra-Descemet's Fluid Drainage with Simultaneous Air Injection: An Alternative Treatment for Descemet's Membrane Detachment.

In this report, we present an alternative technique to manage Descemet's membrane detachment (DMD). We call the technique supra-Descemet's fluid drainage with intracameral air injection. Under topical anesthesia, we injected air through the stab incision to fill 2/3 of the anterior chamber. Then we inserted the tip of a curved 10/0 needle through the corneal surface (entry angle at 45 degrees) into the supra-Descemet's area 3 times to drain this fluid. In our method, we neither injected expanding gas or viscoelastic nor used a suture. Consequently, there was little chance for suture-induced astigmatism or increased intraocular pressure. This technique may be considered a relatively safe and simple surgical method for the management of postoperative DMD.

Simulation of flow field during irrigation/aspiration in phacoemulsification using computational fluid dynamics.

PURPOSE: To provide the details of the flow field in the anterior chamber during irrigation/aspiration (I/A) in phacoemulsification using computational fluid-dynamics methods. SETTINGS: School of Mechanical Engineering, Shiraz University, Dr. Khodadoust Eye Hospital, Shiraz, Iran, and Clarkson University, Potsdam, New York, USA. DESIGN: Theoretical study. METHODS: A 3-dimensional model for the irrigating cannula, anterior chamber, capsular bag, and aspiration cannula was developed. The corresponding mathematic equations were solved numerically, and the details of the flow field were evaluated. The simulation was performed for coaxial and bimanual I/A systems with various flow rates. The pressure flow rate curve was evaluated, and the possibility of an unstable anterior chamber in different cases was assessed. RESULTS: The effects of flow turbulence on the corneal endothelium were lower for the coaxial handpiece. That is, inner placement of irrigation cannula tip lowered the effect of turbulence on the cornea. CONCLUSIONS: Assessment of the fluid dynamics of I/A using computational fluid dynamics provided details that cannot be obtained with the available experimental and analytic methods.

Fyodorov-Zuev keratoprosthesis implantation: long-term results in patients with multiple failed corneal grafts.

BACKGROUND: The long term results of the Fyodorov-Zuev keratoprosthesis are presented for ten patients with repeated graft failures. METHODS: The study took place at Dr Khodadoust Eye Hospital. The Fyodorov-Zuev keratoprosthesis was implanted in ten patients with repeated graft failures, including seven patients with old trachoma, two patients with chemical injury, and a patient with thermal injury. The outcome measures were visual acuity, retention, and complications of the keratoprosthesis. RESULTS: Preoperative best-uncorrected visual acuity (BUVA) ranged from counting fingers to light perception (median: light perception). The keratoprosthesis dramatically improved vision in most patients. Patients retained BUVA of 20/200-20/50 in 50%, 20/60-20/100 in 30%, 20/200 in 10% and 20/400 in 10%. Overall, 90% had 1 year postoperative vision of 20/200 or better. 70% of cases had BUVA of 20/200 or better at the last follow-up (average 52 months). Of ten keratoprosthesis implanted, three have been removed, and as a result, retention rate was 70% during average follow-up of 52 months .The most common postoperative complications were retroprosthetic membrane formation (40%), uveitis (20%), glaucoma (20%), tissue overgrowth (20%), early leakage (20%), late leakage (20%), aseptic necrosis (20%), retinal detachment (10%), endophthalmitis (10%), and granulation tissue growth (10%). CONCLUSIONS: Fyodorov-Zuev keratoprosthesis is an effective means of managing repeated corneal graft failure.

Brain-derived neurotrophic factor as a biomarker in primary open-angle glaucoma.

PURPOSE: To introduce a novel biomarker for screening of primary open-angle glaucoma (POAG) by detecting and measuring brain-derived neurotrophic factor (BDNF) in the serum of normal subjects and patients with early stage of glaucoma. METHODS: Twenty-five glaucoma patients as the case group and 25 age- and sex-matched normal persons as the control group were tested. The control group comprised 19 men and 6 women, with the mean age of 59.32 ± 11.8 years and without any apparent ocular or systemic diseases. The case group comprised 20 men and 5 women, with the mean age of 59.64 ± 11.56 years, who were assessed by routinely performed clinical and paraclinical investigations. BDNF levels in serum were determined by enzyme-linked immunosorbent assay using monoclonal antibodies specific for BDNF. RESULTS: The mean of BDNF levels in the serum was 27.16 ± 5.53 ng/mL in the control subjects and 18.42 ± 4.05 ng/mL in the subjects with the early stage glaucoma. A statistically significant difference was evident between the two groups (p < 0.05). We found no significant differences in serum BDNF levels according to the subjects' age, gender, duration of the glaucoma, mean intraocular pressure, and blood pressure (p > 0.05). Glaucoma patients who had lower serum BDNF concentration had disclosed a significant negative correlation with pattern standard deviations. CONCLUSIONS: We conclude that BDNF in the serum might be a useful biochemical marker for early detection of POAG. We also propose that this might be a reliable, time efficient, and cost-effective method for diagnosis, screening, and assessing the progression of POAG. However, more studies and trials are needed to investigate these factors in greater detail.

Novel materials to enhance corneal epithelial cell migration on keratoprosthesis.

PURPOSE: To introduce a new modification for silicone optical core Keratoprosthesis. METHODS: Using mixtures of 2-hydroxyethyl methacrylate and acrylic acid polydimethylsiloxane (PDMS) films were modified with two-step oxygen plasma treatment, and then type I collagen was immobilised onto this modified surfaces. Both the biocompatibility of the modified films and cell behaviour on the surface of these films were investigated by in vitro tests, and formation of epithelial cell layer was evaluated by implantation of the modified films in the corneas of 10 rabbits. RESULTS: In vitro studies indicated that the number of attached and proliferated cells onto modified PDMS in comparison with the unmodified PDMS significantly increased. Histological studies showed that corneal epithelial cells migrated on the anterior surface of the modified films after 1week. The corneal epithelial cell formed an incomplete monolayer cellular sheet after 10days. A complete epithelialisation on the modified surface was formed after 21days. The epithelial layer persisted on the anterior surface of implant after 1-month and 3-month follow-up. CONCLUSION: This method may have potential use in silicone optical core Keratoprosthesis.

Magnet-assisted capsular bag fixation to manage limited zonular weakness during phacoemulsification.

A new technique to manage limited zonular weakness during phacoemulsification is presented in this report. The technique, called magnet-assisted capsular bag fixation, uses the magnetic implant to stretch and fixate the capsular bag over the zonular dehiscence area for patients with limited zonular disruption, which stabilizes the capsular bag and facilitates cataract extraction.

Brain-derived neurotrophic factor in patients with normal-tension glaucoma.

PURPOSE: The aim of this study was to detect and measure brain-derived neurotrophic factor (BDNF) in the tears of normal subjects and patients with normal-tension glaucoma (NTG). MATERIALS AND METHODS: Twenty patients with NTG as the case group and 20 normal subjects with the same age range as the control group were tested. The control group consisted of 16 men and 4 women, ranging in age from 40 to 75, without any apparent ocular or systemic disease. The case group consisted of 15 men and 5 women, ranging in age from 45 to 74. BDNF levels in tears were determined by enzyme-linked immunosorbent assay using monoclonal antibodies specific for BDNF (R&D Systems, Minneapolis, Minnesota). RESULTS: The mean level of BDNF detected in the tears of the normal subjects was 77.09 +/- 4.84 ng/mL and the BDNF levels in the tears of case group were 24.33 +/- 1.48 ng/mL (P < 0.001). CONCLUSION: We suggest that BDNF in the tears might be a useful biochemical marker for early detection of normal-tension glaucoma (NTG).

Evaluation of transcutaneous electrical simulation to improve recovery from corneal hypoesthesia after LASIK.

PURPOSE: To evaluate the efficacy, and safety of transcutaneous electrical stimulation (TES) to accelerate corneal nerve regeneration and improved recovery from corneal hypesthasia after laser-assisted in situ keratomileusis (LASIK). SETTING: Khodadoust Eye Hospital, Shiraz, Fars, Iran METHODS: This prospective, randomized, clinical study comprised 40 eyes of 20 patients scheduled to undergo bilateral LASIK. In each patient, one eye was randomly assigned to receive transcutaneous electrical stimulation (20 HZ) for 60 minutes, and the other eye allocated as control. Corneal sensitivity was measured using the Cochet-Bonnet esthesiometer in four areas outside and five areas inside the LASIK flap preoperatively, and at 1 day, 1 week, 1 month, and 3 months postoperatively. Best-corrected visual acuity and the incidence of adverse events were noted at each visit. RESULTS: For all four points outside the LASIK flap, normal corneal sensitivity was maintained throughout the study; no significant difference was found between the study eyes and the control eyes at these points (P > 0.05). All points within the LASIK flap except the point closest to the hinge demonstrated profound corneal hypoesthesia at 1 day, 1 week, and 1 month postoperatively, with no differences noted between the control and study eyes (P > 0.05). After 3 months, points within the flap had statistically significantly better corneal sensitivity in the study group than in the control group (P < 0.05). CONCLUSIONS: Transcutaneous electrical stimulation significantly improves corneal sensitivity at 3 months after LASIK. This may be due to accelerated corneal nerve regeneration by electrical stimulation.

Noxious compounds in exhaled air, a potential cause for ocular manifestations of H. pylori gastrointestinal infection.

Helicobacter pylori infection is one of the most common chronic bacterial infections worldwide. In the past few years, a variety of extradigestive disorders have been associated with H. pylori infection. This infection has also been linked to some ophthalmic disorders, including glaucoma, central serous chorioretinopathy, uveitis and blepharitis. Several possible theories to explain pathogenetic mechanism underlying the observed associations have been provided. H. pylori infection causes elaboration of some noxious compounds, including ammonia, hydrogen nitrate and hydrogen cyanide, in exhaled breath of infected individuals. Herein we hypothesize that chronic exposure of ocular surface to these compounds may explain some ophthalmic and also respiratory manifestations of the chronic gastrointestinal infection.