Coupled position and attitude control of a servicer spacecraft in rendezvous with an orbiting target.

Rendezvous is one of the fundamental phases of on-orbit servicing (OOS) missions. Since it requires high accuracy and safety, modeling is an indispensable part. Therefore, this article puts forward an approach for boosting the exactitude of the final proximity phase of a servicer spacecraft using precise modeling. Unlike other similar works that solely use linear models to design controllers, this paper employs a fully nonlinear model and considers most possible uncertainties and disturbances. In this regard, first a complete nonlinear relative pose (i.e., concurrent position attitude) motion dynamic is developed, which includes (1) the role of the reaction wheels and (2) the major environmental force and torque model. Second, taking the thruster's adverse torque into account, two sliding mode-based control techniques with different nonlinear sliding surfaces are designed. Moreover, the Lyapunov stability criterion is used to handle high nonlinearity effects, control input saturation, actuator misalignment, external disturbance torque/force, measurement error, uncertainties of both inertia parameters, and control inputs. Even the PWPF modulator of the thrusters has been considered to make the outcomes more realistic. Finally, three different scenarios are comprehensively simulated to illustrate the feasibility and efficiency of the designed scheme. The results prove that the proposed closed-form controller is more executable to implement than other existing approaches.

Absorbable suture for band tightening of scleral buckling in pseudophakic rhegmatogenous retinal detachment: a modified surgical technique and a 6-month follow-up.

Background: Rhegmatogenous retinal detachment (RRD) is a separation of the neurosensory retina from the retinal pigment epithelium as a result of liquid vitreous passing through a retinal break. Scleral buckling surgery (SB) is a conventional treatment for RRD. In SB, a silicon explant is used to indent the sclera, reduce vitreous traction, and close the retinal break, and an encircling band is used circumferentially, leading to myopia. This study aimed to evaluate the functional and biometric outcomes after SB with absorbable band-tightening sutures in patients with pseudophakic RRD. Methods: In this prospective interventional study, we included pseudophakic eyes with RRD treated surgically with SB and a temporary encircling band using a 6-0 absorbable Vicryl suture to tighten the band, instead of conventional permanent suture tightening. Anterior chamber depth (ACD), axial length (AL), intraocular pressure (IOP), spherical equivalent refractive error (SER), and best-corrected distance visual acuity (BCDVA) were measured preoperatively and at 1 day, 2 weeks, 3 months, and 6 months postoperatively. Results: We included 30 eyes of 30 patients with a mean (standard deviation [SD]) age of 66.1 (10.5) years who underwent SB with an absorbable band-tightening suture for pseudophakic RRD. Significant increases in AL and ACD were observed at 2 weeks after surgery, with a significant decline in values thereafter; however, at the 6-month follow-up, the values were significantly higher than those at baseline (all P < 0.05). Based on the Vicryl tension and its hydrolysis, mean (SD) SER at 2 weeks postoperatively was significantly more myopic than at baseline (-5.8 [1.6] D versus +1.3 [1.8] D). However, the mean (SD) SER decreased significantly throughout the 6-month follow-up (all P < 0.05), and it reached -1.8 (0.9) D, which was comparable with the mean baseline SER (P = 0.140). The participants experienced significant improvement in BCDVA throughout the follow-up period (all P < 0.05). Conclusions: Using an absorbable suture to tighten the encircling band in patients with pseudophakic RRD can reduce postoperative myopia without adversely affecting the anatomical or functional outcomes. Future comparative studies with larger sample sizes and longer postoperative follow-up are needed to verify these findings.

Frequency of retinopathy of prematurity at a tertiary referral center.

Background: With advances in medical facilities and increased survival of premature infants, the prevalence of retinopathy of prematurity (ROP) has increased. This study aimed to determine the frequency of ROP and its associated risk factors. Methods: This descriptive-analytical, retrospective study included all premature infants with a birth weight (BW) ≤ 2,500 g and/or gestational age (GA) ≤ 35 weeks who were referred to Imam Khomeini Hospital in Ahvaz, Iran, for ROP screening over a 7-year period from April 2013 to April 2020. Demographic criteria, associated risk factors, and findings of eye examinations were collected and analyzed. Results: Of the 812 at-risk infants screened, 807 met the inclusion criteria. ROP was observed in 316 (39.0%) of the 807 premature infants, with types I and II in 142 (45.0%) and 174 (55.0%) infants, respectively. The mean (SD) GA (29.6 [2.5] weeks versus 30.7 [2.5] weeks) and BW (1,203.6 [382.8] g versus 1,333.5 [386.5] g) were significantly lower in infants with ROP than in those without ROP (both P < 0.001). GA (r = 0.80; P < 0.001) and BW (r = 0.85; P < 0.001) had a strong positive correlation with ROP, and the correlation increased as GA and BW decreased (all P < 0.001). Associated risk factors in infants with ROP, in order of frequency, were oxygen therapy (22.8%), respiratory distress (16.1%), phototherapy (14.6%), blood transfusion (5.7%), apnea (4.1%), mechanical ventilation (1.6%), and intraventricular hemorrhage (0.9%). Multivariate regression analyses showed low GA and BW (both P < 0.05) as independent predictors of ROP. Conclusions: The frequency of ROP in premature infants was slightly higher than the average range reported for domestic and foreign statistics. Low BW and GA were independent predictors of ROP.

Prevention of Corneal Neovascularization; a Preliminary Experimental Study in Rabbits.

The purpose of this study was to compare the effects of propranolol, timolol and bevacizumab with betamethasone to prevent corneal neovascularization (CNV) in rabbits. This study was performed on 28 male rabbits. CNV was induced by three 7-0 silk sutures 2 mm long and 1 mm distal to the limbus. Animals were randomly divided into 4 groups of propranolol + betamethasone, timolol + betamethasone and bevacizumab + betamethasone and betamethasone alone. Eye drops were started from the first day of study. On 7th, 14th, 21st, 28th, 35th and 42nd days, vascular progression, time of neovascularization and vascular area were evaluated and compared with the control group (betamethasone alone). There was a significant reduction in the area of ​​neovascularization in the timolol and bevacizumab groups compared to the control group (P-value = 0.05, P=0.047, respectively). Also, regarding vascular progression, there was a significant decrease in the timolol and bevacizumab groups (P-value = 0.014, P=0.002, respectively). Regarding delayed onset of neovascularization, there was a significant difference in the timolol and bevacizumab group in rabbits (P-value = 0.04, P=0.00, respectively). In conclusion, the use of timolol and bevacizumab drops besides betamethasone can delay neovascularization and decrease the length of corneal vascularization in rabbits.

Investigating the effects of glaucomatous damage on the multifocal visual evoked potential parameters.

PURPOSE: To investigate the effects of glaucomatous damage on the mfVEP parameters of patients suffering from primary open-angle glaucoma (POAG). METHODS: Fifteen healthy subjects and 15 patients with unilateral POAG participated in this study. In addition, routine ophthalmological examinations including visual acuity, anterior segment examination, posterior segment examination, intraocular pressure, mfVEP with electrophysiological system, RETI-port/Scan 21, and visual field test with automated Humphrey ZEISS HFA II 750i Perimeter were also performed. RESULTS: The results show that there was a strong correlation between the ∆MDs and the number of abnormal points with the ∆amplitudes more than 256 nV, in patients (n = 15, r = 0.802, p < 0.05), but no correlations were found between the mean sensitivity differences (ΔPSDs) and mfVEP parameters. CONCLUSIONS: Comparing the monocular mfVEP responses from both eyes is an appropriate method to detect unilateral damage. Achievement of more development and making the mfVEP test more functional can be a solution for early diagnosis in most of the eye diseases.

Topical Timolol Inhibits Corneal Neovascularization in Rabbits.

Timolol is a non-selective beta-adrenergic antagonist that is similar to propranolol. The mechanism through which these drugs act on the regression of neovascularization is largely unknown. However, it is thought that the drugs may act through vascular endothelial growth factor signaling, vasoconstriction, and vascular endothelial cell apoptosis. The aim of this study was to determine the effect of timolol on corneal neovascularization in rabbits. Neovascularization was induced in the eyes of 20 rabbits. Next, the rabbits were divided into two groups: the timolol (experimental) group received eye drops containing timolol 0.5% twice per day; and the saline (control) group received saline drops twice per day for two weeks. After 7 days, the mean area of corneal neovascularization (presented as a percentage relative to baseline) was significantly lower in the timolol group than in the saline group (4.63 ± 4.61% versus 58.39 ± 6.31%, P < 0.001). After 2 weeks, the mean area of corneal neovascularization was 0.85 ± 1.33% in the timolol group and 1.73 ± 2.06% in the saline group (P = 0.315). After the first week of treatment, timolol significantly reduced the area of neovascularization compared to control. Timolol may increase the rate of recovery from corneal neovascularization.

The Association Between Primary Open Angle Glaucoma and Clustered Components of Metabolic Syndrome.

PURPOSE: There is conflicting evidence whether components of metabolic syndrome (MetS) increase or decrease the risk of primary open-angle glaucoma (POAG). The aim of the present study was to determine the association between metabolic syndrome and primary open-angle glaucoma. METHODS: A total of 200 participants comprising 100 controls and 100 patients with POAG documented by clinical tests and examined by an experienced ophthalmologist using standard ophthalmologic equipment were included in the study. MetS was defined and based on ATP III criteria and POAG was defined by the criteria of the International Society of Geographic and Epidemiological Ophthalmology (ISGEO). The data were entered into the SPSS software and analyzed. RESULTS: The prevalence of MetS in the glaucoma group was 53% in comparison to 38% in the control group (p=0.037). MetS was associated with an increased odds ratio for an IOP higher than 21 mmHg (OR: 1.72; 95% CI 1.03-2.79; p=0.034). The mean IOP was 24.91±4.29 mmHg in the patients without MetS, and 27.23±4.81 mmHg in those with MetS (p=0.027). The mean values of CCT were 603.64±63.16 µm in MetS patients and 579.27±72.87 µm in controls (p=0.018). CONCLUSION: Data showed an increased prevalence of components of metabolic syndrome in patients with glaucoma. The mechanisms underlying these associations need to be established in future studies. Our results support the recommendation that patients with metabolic syndrome undergo regular ophthalmological exams to monitor for the onset or progression of glaucoma.

Isolation and Identification of Pathogenic Filamentous Fungi and Yeasts From Adult House Fly (Diptera: Muscidae) Captured From the Hospital Environments in Ahvaz City, Southwestern Iran.

Musca domestica L., 1758 is capable of transferring a number of pathogenic viruses, bacteria, fungi, and parasites to animals and humans. The objective of this study was to isolate and identify medically important filamentous fungi and yeasts from adult M. domestica collected from two wards of three hospital environments in Ahvaz city, Khuzestan Province, southwestern Iran. The common house flies were caught by a sterile net. These insects were washed in a solution of 1% sodium hypochlorite for 3 min and twice in sterile distilled water for 1 min. The flies were individually crushed with sterile swabs in sterile test tubes. Then 2 ml of sterile normal saline (0.85%) was added to each tube, and the tube was centrifuged for 5 min. The supernatant was then discarded, and the remaining sediment was inoculated with a sterile swab in the Sabouraud's dextrose agar medium containing chloramphenicol. Isolation and identification of fungi were made by standard mycological methods. In this research, totally 190 M. domestica from hospital environments were captured. In total, 28 fungal species were isolated. The main fungi isolated were Aspergillus spp. (67.4%), Penicillium sp. (11.6%), Mucorales sp. (11%), Candida spp. (10.5%), and Rhodotorula sp. (8.4%). Among the house flies caught at the hospitals, about 80% were found to carry one or more medically important species of fungi. This study has established that common house flies carry pathogenic fungi in the hospital environments of Ahvaz. The control of M. domestica in hospitals is essential in order to control the nosocomial fungal infections in patients.

Incidence of retinopathy of prematurity and risk factors in the South-Western region of iran.

AIMS: The aim of this study was to report the incidence of retinopathy of prematurity (ROP) and the contribution of various risk factors to ROP in the south-western region of Iran. MATERIAL AND METHODS: This cross-sectional case-control series reviewed all low birth weight (LBW, ≤2000 g) neonates and/or neonates less than 32 weeks gestational age who had been hospitalized in the Neonatal Intensive Care Unit from 2006 to 2010. The cohort was divided into infants without ROP (nonROP group) and infants with ROP (ROP group). Infants were first examined by a group of pediatric ophthalmologists 6 weeks after delivery, and then were followed every 1-2 weeks until death, discharge or complete retinal avascularization. If an infant developed ROP, further examinations were performed based on the Early Treatment for Retinopathy of Prematurity Study protocol. Demographic data, medical treatment, and ophthalmic disorders were all statistically analyzed. RESULTS: A total of 576 infants met the criteria for evaluation. Of 576 total patients, 183 infants (32%) (88 males, 95 females) had ROP. There were significant differences between groups in gestational age, body weight, and duration of oxygen administration, and sepsis (P<0.05). Male/female ratio, single and multiple births, and jaundice, phototherapy, and blood transfusion were not significant. The majority of ROP was stage I or II (137, 74.8%). Stage III or greater developed in 46 infants (25.1%) [Note: The ocular history and ocular outcomes are not risk factors.] CONCLUSIONS: The incidence of ROP in this study is higher than that in other parts of the world. Awareness and knowledge of ROP and its relative risks need to be reinforced in ophthalmologists and other health practitioners.

Iris Claw versus Scleral Fixation Intraocular Lens Implantation during Pars Plana Vitrectomy.

PURPOSE: To compare the outcomes of iris claw anterior chamber intraocular lens (IC-ACIOL) with that of scleral fixation posterior chamber intraocular lens (SF-PCIOL) implantation during pars plana vitrectomy (PPV) as initial surgery to correct aphakia. METHODS: Twelve patients with complicated cataract surgery or trauma who hadsuffered nucleus, whole crystalline lens or intraocular lens (IOL) drop into the vitreous cavity, and undergone PPV with IC-ACIOL implantation over a period of one year were evaluated for the purpose of this study. Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), central corneal thickness (CCT), spherical equivalent (SE) refractive error, astigmatism and complications were recorded. The results were compared to outcomes of another group of 13 patients who had previously undergone PPV with SF-PCIOL implantation. RESULTS: Mean improvement of UCVA was greater in IC-ACIOL eyes as compared tothe SF-PCIOL group (-1.17±0.28 versus -0.89±0.21 logMAR, P=0.01), corresponding values for postoperative BCVA were 0.24±0.17 and 0.44±0.22 logMAR (P=0.041), respectively. Average postoperative SE was comparable in the IC-ACIOL and SF-PCIOL groups at 0.6±1.03 and 0.56±1.23 diopters, respectively (P=0.290). However, 10 (83.3%) IC-ACIOL eyes versus 6 (46.1%) SF-PCIOL eyes had SE within 1 diopter of emmetropia (P=0.048). Mean postoperative increase in CCT was comaparble between the study groups (P=0.126). CONCLUSION: In the absence of sufficient capsular support, the use of an IC-ACIOLfor correction of aphakia during PPV can be a good alternative and seems to entail better visual outcomes as compared to SF-PCIOL.