Purpose: To report the outcomes of pars plana insertion of Aurolab aqueous drainage implant (AADI) in adults with refractory glaucoma by the novel technique of making scleral tunnel instead of patch ...graft to cover the tube to prevent its migration. Methods: A retrospective study was done between April 2016 and April 2018 on patients with ≥12 months of follow-up. The main outcome measure was a surgical failure at 12 months. The failure was defined as intraocular pressure (IOP) >18 mmHg or IOP ≤5 mmHg on two consecutive follow-up visits after 3 months, reoperation for glaucoma, loss of light perception vision, or implant explantation. Alternate definitions of failure including IOP >21 and IOP >15 mmHg were also considered. Results: The study included 32 eyes of 32 patients. The mean age was 46.2 ± 17.5 years. The most common etiology is traumatic glaucoma (12 eyes, 37.5%). The mean preoperative IOP and anti-glaucoma medications were 43.3 ± 10.3 and 3.4 ± 0.5 mmHg, respectively; both the parameters at the final follow-up were reduced to 15.2 ± 8.1 and 1.6 ± 0.5 mmHg. The Kaplan-Meier survival estimates demonstrated that the cumulative probability of failure was 15.6% (95% CI; 6.8-33.5%) at 3 months, 18.7% (95% CI; 8.9-37.0%) at 6 months, and 25.0% (95% CI; 13.4-43.8%) at 12 months. Conclusion: Pars plana AADI implantation with a newer modification technique is a useful procedure in reducing IOP and the number of anti-glaucoma medications in the eyes with refractory glaucoma. The visual acuity may be stabilized with the concurrent treatment of posterior segment pathology.
Glaucoma drainage devices (GDDs) are used for managing refractory glaucoma due to failed trabeculectomy, neovascular glaucoma, traumatic glaucoma, and secondary glaucoma post keratoplasty. Aurolab ...aqueous drainage implant (AADI) is a nonvalved drainage implant conventionally implanted with the tube placed in the anterior chamber. Studies about the outcome of the various aqueous drainage devices implanted in the anterior chamber have reported complications such as tube extrusion, migration, blockage, erosion, and corneal decompensation. We propose modifying the conventional GDD implantation technique by placing the tube in the vitreous cavity, thereby negating the risk of anterior segment complications in patients with refractory glaucoma whose anterior segment is already compromised. Another novel approach implemented in this technique was making a scleral tunnel instead of using a scleral or corneal patch graft to cover the tube to prevent its migration. This article describes the surgical steps of this technique and its advantages, along with a surgical video.
One-minute ophthalmology: "To PI or not to PI" Ravindran, Ram Sudarshan; Aswin, P R; Khadar, Syed Mohideen Abdul
Indian journal of ophthalmology,
03/2024, Letnik:
72, Številka:
3
Journal Article
Tamil Nadu is one of the states in India, where the diabetic retinopathy (DR) project was implemented in the Tirunelveli District. Aravind Eye Hospital, Tirunelveli was the mentoring institution and ...ophthalmology department of Tirunelveli Medical College and Hospital (TVMCH) was the implementing partner. The objective of the project was to develop a district level model for building capacity at the government health system for effective screening, diagnosis and management (primary to tertiary) of diabetic retinopathy. The DR screening, counseling, referral and follow-up tasks were included in the scope of Non- Communicable Disease (NCD) nurses at the respective Community Health Centres and Primary Health Centres using the tele-medicine platform. During the project period (December 2016 to June 2019), 8,574 people with diabetes were registered at the 18 CHCs/PHCs. 6,462 (75.4% of those registered) were screened by NCD staff. The government has agreed to scale up services in 3 more districts.
•Fatigue strength was reduced by a factor of 1.5 owing to gas pore defects.•Fatigue life can be correlated with the stress intensity factor range of the crack initiating pore.•The fatigue limit vs. ...pore size relation can be represented by a sigmoidal curve.•Fatigue limit can be predicted by a modified El-Haddad model.
This study was aimed at investigating the effect of internal porosity on the fatigue strength of wire + arc additive manufactured titanium alloy (WAAM Ti-6Al-4V). Unlike similar titanium alloys built by the powder bed fusion processes, WAAM Ti-6Al-4V seldom contains gas pores. However, feedstock may get contaminated that may cause pores of considerable size in the built materials. Two types of specimens were tested: (1) control group without porosity referred to as reference specimens; (2) designed porosity group using contaminated wires to build the specimen gauge section, referred to as porosity specimens. Test results have shown that static strength of the two groups was comparable, but the elongation in porosity group was reduced by 60% and its fatigue strength was 33% lower than the control group. The stress intensity factor range of the crack initiating pore calculated by Murakami’s approach has provided good correlation with the fatigue life. The kink point on the data fitting curve corresponds well with the threshold value of the stress intensity factor range found in the literature. For predicting the fatigue limit, a modified Kitagawa-Takahashi diagram was proposed consisting of three regions depending on porosity size. Critical pore diameter was found to be about 100 µm.
Abstract Additive manufacturing (AM) of Al–Mg–Sc alloys has received considerable interest from the aerospace industry owing to their high specific strength and suitability for AM processes. This ...study has investigated the fatigue crack growth behavior in an Al–Mg–0.3Sc alloy made by wire and arc additive manufacturing. Tests were conducted with two different crack orientations at cyclic load ratios of 0.1 and 0.5. At the lower load ratio, the horizontal crack showed a faster growth rate owing to the smaller grains and coarser second‐phase particles that the crack tip had encountered when it propagated along the material build direction. The anisotropy in crack growth rate was mainly caused by the grain size effect. When the applied stress intensity factor range exceeded the value of 10 MPa m 1/2 , an isotropic crack growth rate between the two crack orientations was measured. This is due to the microstructural influence being overcome by the governing parameter of fracture mechanics. At the higher load ratio of 0.5, crack growth rate is isotropic, and the threshold stress intensity factor range was much lower than that tested under load ratio 0.1. Finally, the modified Hartman–Schijve equation has been successfully employed to represent the crack growth rates in all three regions.
Highlights A newly developed aluminum alloy by a wire‐based additive manufacturing process; Grain size and second‐phase particle distribution affect the fatigue crack growth rate; A modified equation to be employed to represent the experimental data.
Cold spray (CS) is a solid-state additive material deposition technique, which has gained attention in the aerospace industry as a potentially viable technology for structural repair of high-value ...parts made of high-strength alloys such as Ti-6Al-4V (Ti-64). Residual stresses build up in the substrate and deposited materials resulting from the CS process can influence the integrity of a coating or repair. However, the nature, magnitude and distribution of residual stresses in Ti-64/Ti-64 CS repairs are currently unknown. This study aims to evaluate the effects of geometrical variables (i.e. the number of CS layers, CS layer thickness, and substrate thickness) and track pattern on the magnitude and distribution of residual stresses in CS deposit-substrate assemblies. Through-thickness stress distributions were measured experimentally by neutron diffraction and contour method. Furthermore, a comparison among different residual stress build-up mechanisms induced by CS processes has been discussed for different combinations of substrate and deposit assemblies. An analytical model based on the force and moment equilibrium requirements was used to interpret the experimental stress profiles and to predict the residual stress distribution. It was found that residual stresses are highly tensile near the free surface of the Ti-64 deposits as well as towards the bottom of the substrate, and compressive near the interface region. Although all the specimens showed similar stress distribution, the magnitudes were found to be higher in one or more of the following cases: specimens with a higher number of CS layers, lower substrate thickness, higher layer thickness (i.e. at lower scanning speed), and deposited with a horizontal track pattern.
•Residual stresses induced by cold spraying of Ti-6Al-4 V were evaluated using neutron diffraction and contour method.•A parametric study was performed on the influence of geometrical and process variables on residual stresses.•An analytical method was used to interpret the experimental results and to compare different stress build-up mechanisms.
This paper reports the effect of as-deposited surface conditions on the fatigue strength of an additively manufactured titanium alloy, Ti-6Al-4V (WAAM Ti64). First, the local stress concentration ...caused by the surface waviness was quantified using a metrology technique and computer modelling. Fatigue tests were conducted under bending loads at a cyclic load ratio of 0.1. The applicability of two predictive methods was the focus of this study. The traditional notch stress method was unable to predict the correct S-N curve trend slope, which could be attributed to the early crack initiation from the troughs on the as-built surface, with crack propagation being the dominant failure mechanism. By treating the troughs as small cracks, the fracture mechanics approach delivered good predictions at every applied stress level. Surface machining and polishing may not always be practical or required; it depends on the applications and service load levels. This research demonstrated that the fracture mechanics approach can be used for predicting the fatigue life of WAAM titanium alloys in as-built conditions and, hence, can be a tool for decision making on the level of surface machining.
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