Prevalence and severity of diabetic retinopathy at first presentation to vitreoretinal services in Bhutan: a 3-year national study.

PURPOSE: To determine the prevalence and severity of diabetic retinopathy (DR) at first presentation among diabetic patients attending national vitreoretinal (VR) services in Bhutan STUDY DESIGN: Retrospective cross-sectional study METHODS: We included all diabetic patients in Bhutan who presented for retinal evaluation for the first time over a 3-year period (2013-2016). Data including demography, clinical details, diagnostic tests, and clinical staging of DR were analyzed. RESULTS: A total of 843 diabetic patients, aged 57.2 ± 12.0 (range 18-86) years, were enrolled. The majority were male (452, 53.6%; cumulative frequency [cf] 391, 46.4%; P = .14) and from urban settings (570, 67.6%; cf 273; 32.4%) and did not have modern schooling (555, 65.8%). Hypertension was the most common systemic comorbidity (501, 59.4%). The prevalence of DR was 42.7%, with mild nonproliferative DR (NPDR) being the most common type (187, 51.9%), followed by moderate NPDR (88, 24.4%) and proliferative DR (45, 12.5%). In addition, 120 patients had clinically significant macular edema (CSME), with a prevalence of 14.2%. Best-corrected visual acuity (BCVA) of 6/60 or worse occurred in 231 eyes (13.7%), and 41 patients (4.86%) had BCVA of 6/60 or worse bilaterally due to DR/CSME. A logistic regression model indicated that the major determinant of DR was the duration of diabetes, the odds rising by 1.27× with each year of disease (P < .0001). CONCLUSION: The prevalence of DR, including CSME, was high. Although a national DR screening program is established in Bhutan, there is a need to accelerate health education, community screening, and referral systems to reduce the prevalence of DR and CSME.

Severity of age-related macular degeneration at first presentation in Bhutan: a 3-year national study.

BACKGROUND: Medical services are still developing in Bhutan. There is no published national report on age-related macular degeneration (AMD). We therefore aim to determine the demographic characteristics and severity of AMD at first presentation among Bhutanese patients attending their recently inaugurated vitreoretinal (VR) clinics over a 3-year national survey, and to inform national health policy to develop suitable health program to prevent AMD-related blindness and visual impairment. METHODS: A retrospective cross-sectional consecutive case series study was conducted on all new AMD cases in Bhutan. If a patient presented with asymmetrical AMD, the eye with more severe AMD was considered. If both the eyes had the same severity one eye was chosen randomly. Collection of demographic data and clinical details including diagnostic testing (fundus photography, OCT and fluorescent angiography) and clinical staging were performed. RESULTS: Of 521 new AMD patients aged 71.9 ± 11.3 years, 306/521 (58.7%) were males (p = 0.005). At their first presentation, 234/521 patients (44.9%) already had late-stage AMD. Importantly, 69/234 patients (29.5%), that is half of total neovascular AMD (nAMD) patients, had disciform scars (DS) which were beyond treatment, and 7/234 patients (3.0%) had geographic atrophy (GA). Seven patients had retinal pigment epithelium tear at presentation. Fourteen of nineteen polypoidal choroidal vasculopathy (PCV) patients were younger than 50 years. CONCLUSIONS: Half of nAMD cases presented as DS not amenable to the treatment. Many potentially treatable nAMD patients had already lost central vision and were legally blind. Young people with PCV losing vision early in life with longer morbidity-affected life and socio-economic burden was concerning. GA and DS cases need visual rehabilitation to improve their QoL. Incorporating a screening program for AMD with effective health education, and maintaining a national AMD Registry, would potentially lower AMD-related blindness and visual impairment.

Optimization of the Chronic Kidney Disease-Peritoneal Dialysis App to Improve Care for Patients on Peritoneal Dialysis in Northeast Thailand: User-Centered Design Study.

BACKGROUND: The prevalence of peritoneal dialysis (PD) in Thailand is increasing rapidly in part because of Thailand's Peritoneal Dialysis First policy. PD is a home-based renal replacement therapy in which patients with chronic kidney disease perform up to 4 exchanges of dialysate fluid per day in the peritoneal cavity. Overhydration is one of the most common complications in patients on PD and is associated with increased morbidity and mortality. To monitor hydration status, patients collect hydration metrics, including body weight, blood pressure, urine output, and ultrafiltration volume, from each dialysis cycle and enter this information into a PD logbook. This information is reviewed bimonthly at PD clinic appointments. The chronic kidney disease-PD (CKD-PD) app with near-field communication (NFC) and optical character recognition (OCR) was developed to automate hydration metric collection. The information was displayed in the app for self-monitoring and uploaded to a database for real-time monitoring by the PD clinic staff. Early detection and treatment of overhydration could potentially reduce the morbidity and mortality related to overhydration. OBJECTIVE: This study aims to identify usability issues and technology adoption barriers for the CKD-PD app with NFC and OCR and a monitoring system and to use this information to make rapid cycle improvements. METHODS: A multidisciplinary team of nephrologists, PD clinic nurses, computer programmers, and engineers trained and observed 2 groups of 5 participants in the use of the CKD-PD app with NFC and OCR and a monitoring system. The participants were observed using technology in their homes in 3 phases. The data collected included the Unified Theory of Acceptance and Use of Technology questionnaire, think-aloud observation, user ratings, completion of hydration metrics, and upload of hydration metrics to the central database. These results were used by the team between phases to improve the functionality and usefulness of the app. RESULTS: The CKD-PD app with NFC and OCR and a monitoring system underwent 3 rapid improvement cycles. Issues were identified regarding the usability of the NFC and OCR data collection, app stability, user interface, hydration metric calculation, and display. NFC and OCR improved hydration metric capture; however, issues remained with their usability. App stability and user interface issues were corrected, and hydration metrics were successfully uploaded by the end of phase 3. Participants' scores on technology adoption decreased but were still high, and there was enthusiasm for the self-monitoring and clinical communication features. CONCLUSIONS: Our rapid cycle process improvement methodology identified and resolved key barriers and usability issues for the CKD-PD app with NFC and OCR and a monitoring system. We believe that this methodology can be accomplished with limited training in data collection, statistical analysis, and funding.

Retinal laser services in Bhutan: a 3-year national survey.

BACKGROUND: We conducted this study to report on the indications and types of retinal laser therapy (RLT) performed in Bhutan, knowing which is critical for proper planning and successful delivery of the services. METHODS: We reviewed the laser registers maintained in the laser rooms and vitreoretinal (VR) operating theatres (including paediatric cases managed under anaesthesia) over three years at the national and the two regional referral hospitals (RRHs). Intraoperative laser treatments (endolaser) were excluded. Patient demography, indications and types of RLT were recorded and quantified. Comparisons of the expected and observed frequencies used Chi-squared tests. RESULTS: A total of 685 patients, including 8 cases of bilateral retinopathy of prematurity (ROP) received RLT. The majority of patients (411 cases, 60.0%, p < 0.0001) were males. The mean age was 54.1 ± 14.1 years, median 56 years. The most common indications for RLT were diabetic retinopathy (DR) and diabetic macular oedema (DMO) (542 cases, 66.0%), followed by retinal vein occlusion (RVO) (91 cases, 13.3%). Pan-retinal photocoagulation was the most common type of RLT performed (337 cases, 49.2%), followed by modified grid laser (207 cases, 30.2%), sectoral laser (41 cases, 6.0%), and prophylactic laser photocoagulation (33 cases, 4.8%). CONCLUSIONS: The majority of patients were within working-age. Common indications for RLT were preventable such as DR, DMO and RVO, indicating need to control systemic diseases such as diabetes, hypertension, and dyslipidaemia. Currently, regular RLT is provided only at the national referral hospital in Thimphu, and periodically in the eastern and central RRHs when the retinal specialist visits. There is need to extend the retinal services to the eastern and central RRHs to improve accessibility and patient coverage in these regions challenged with difficult terrain and poor public transport system.

Pattern of vitreo-retinal diseases at the national referral hospital in Bhutan: a retrospective, hospital-based study.

BACKGROUND: Knowing the pattern and presentation of the diseases is critical for management strategies. To inform eye-care policy we quantified the pattern of vitreo-retinal (VR) diseases presenting at the national referral hospital in Bhutan. METHODS: We reviewed all new patients over three years from the retinal clinic of the Jigme Dorji Wangchuck National Referral Hospital. Demographic data, presenting complaints and duration, treatment history, associated systemic diseases, diagnostic procedures performed, and final diagnoses were quantified. Comparisons of the expected and observed frequency of gender used Chi-squared tests. We applied a sampling with replacement based bootstrap analysis (10,000 cycles) to estimate the population means and the standard errors of the means and standard error of the 10th, 25th, 50th, 75th and 90th percentiles of the ages of the males and females within 20-year cohorts. We then applied t-tests employing the estimated means and standard errors. The 2913 subjects insured that the bootstrap estimates were statistically conservative. RESULTS: The 2913 new cases were aged 47.2 ± 21.8 years. 1544 (53.0%) were males. Housewives (953, 32.7%) and farmers (648, 22.2%) were the commonest occupations. Poor vision (41.9%), screening for diabetic and hypertensive retinopathy (13.1%), referral (9.7%), sudden vision loss (9.3%), and trauma (8.0%) were the commonest presenting symptoms. Coexistent diabetes and hypertension were the most common associated systemic diseases. Haematological tests (blood sugar, HbA1c and lipid profile, 31.8%), OCT (27.4%), refraction (9.9%), B-scan (8.7%), fundus photography (8.0%) were the most commonly performed diagnostic tests. Hypertensive retinopathy (18.9%) was the commonest VR disease, followed by refractive errors referred for retinal evaluation (16.7%), diabetic retinopathy with macular oedema (15.8%), and AMD (11.0%). Retinal detachment was more prevalent in females (83 vs. 41, p = 0.007). Rare vision-threatening diseases like seasonal hyper-acute pan-uveitis also presented. CONCLUSIONS: The developing VR service in Bhutan is challenged by the spectrum of diseases, limited human resources (e.g. one retinal surgeon during the study), and accessibility to tertiary eye-care services, all amidst difficult terrain. Sustained effort and robust coordination among the eye-care professionals, government and non-governmental organisations are critical for optimising VR services, especially as rates of diseases such as diabetes and hypertension grow.

Multimedia Appendix Removal and Editorial Warning Regarding the MMAS Scale (Two-Way Social Media Messaging in Post-Operative Cataract Surgical Patients: A Prospective Interventional Study).

[This corrects the article DOI: 10.2196/jmir.8330.].

Patient Harm in Cataract Surgery: A Series of Adverse Events in Massachusetts.

Massachusetts state agencies received reports of 37 adverse events (AEs) involving cataract surgery from 2011 to 2015. Fifteen were anesthesia related, including 5 wrong eye blocks, 3 cases of hemodynamic instability, 2 retrobulbar hematoma/hemorrhages, and 5 globe perforations resulting in permanent loss of vision. While Massachusetts' reported AEs likely underrepresent the true number of AEs that occur during cataract surgery, they do offer useful signal data to indicate the types of patient harm occurring during these procedures.

Preventing Adverse Events in Cataract Surgery: Recommendations From a Massachusetts Expert Panel.

Massachusetts health care facilities reported a series of cataract surgery-related adverse events (AEs) to the state in recent years, including 5 globe perforations during eye blocks performed by 1 anesthesiologist in a single day. The Betsy Lehman Center for Patient Safety, a nonregulatory Massachusetts state agency, responded by convening an expert panel of frontline providers, patient safety experts, and patients to recommend strategies for mitigating patient harm during cataract surgery. The purpose of this article is to identify contributing factors to the cataract surgery AEs reported in Massachusetts and present the panel's recommended strategies to prevent them. Data from state-mandated serious reportable event reports were supplemented by online surveys of Massachusetts cataract surgery providers and semistructured interviews with key stakeholders and frontline staff. The panel identified 2 principal categories of contributing factors to the state's cataract surgery-related AEs: systems failures and choice of anesthesia technique. Systems failures included inadequate safety protocols (48.7% of contributing factors), communication challenges (18.4%), insufficient provider training (17.1%), and lack of standardization (15.8%). Choice of anesthesia technique involved the increased relative risk of needle-based eye blocks. The panel's surveys of Massachusetts cataract surgery providers show wide variation in anesthesia practices. While 45.5% of surgeons and 69.6% of facilities reported increased use of topical anesthesia compared to 10 years earlier, needle-based blocks were still used in 47.0% of cataract surgeries performed by surgeon respondents and 40.9% of those performed at respondent facilities. Using a modified Delphi approach, the panel recommended several strategies to prevent AEs during cataract surgery, including performing a distinct time-out with at least 2 care-team members before block administration; implementing standardized, facility-wide safety protocols, including a uniform site-marking policy; strengthening the credentialing and orientation of new, contracted and locum tenens anesthesia staff; ensuring adequate and documented training in block administration for any provider who is new to a facility, including at least 10 supervised blocks before practicing independently; using the least invasive form of anesthesia appropriate to the patient; and finally, adjusting anesthesia practices, including preferred techniques, as evidence-based best practices evolve. Future research should focus on evaluating the impact of these recommendations on patient outcomes.

Two-Way Social Media Messaging in Postoperative Cataract Surgical Patients: Prospective Interventional Study.

BACKGROUND: Social media offers a new way to provide education, reminders, and support for patients with a variety of health conditions. Most of these interventions use one-way, provider-patient communication. Incorporating social media tools to improve postoperative (postop) education and follow-up care has only been used in limited situations. OBJECTIVE: The aim of this study was to determine the feasibility and efficacy of two-way social media messaging to deliver reminders and educational information about postop care to cataract patients. METHODS: A total of 98 patients undergoing their first eye cataract surgery were divided into two groups: a no message group receiving usual pre- and postop care and a message group receiving usual care plus messages in a mobile social media format with standardized content and timing. Each patient in the message group received nine messages about hand and face hygiene, medication and postop visit adherence, and links to patient education videos about postop care. Patients could respond to messages as desired. Main outcome measures included medication adherence, postop visit adherence, clinical outcomes, and patients' subjective assessments of two-way messaging. The number, types, content, and timing of responses by patients to messages were recorded. RESULTS: Medication adherence was better in the message group at postop day 7, with high adherence in 47 patients (96%, 47/49) versus 36 patients (73%, 36/49) in the no message group (P=.004), but no statistically significant differences in medication adherence between the groups were noted at preop and postop day 30. Visit adherence was higher at postop day 30 in the message group (100%, 49/49) versus the no message group (88%, 43/49; P=.03) but was 100% (49/49) in both groups at postop day 1 and 7. Final visual outcomes were similar between groups. A total of 441 standardized messages were sent to the message group. Out of 270 responses generated, 188 (70%) were simple acknowledgments or "thank you," and 82 (30%) responses were questions that were divided into three general categories: administrative, postop care, and clinical issues. Out of the 82 question responses, 31 (11%) were about administrative issues, 28 (10%) about postop care, and 23 (9%) about clinical symptoms. All the messages about symptoms were triaged by nurses or ophthalmologists and only required reassurance or information. Patients expressed satisfaction with messaging. CONCLUSIONS: Two-way social media messaging to deliver postop information to cataract patients is feasible and improves early medication compliance. Further design improvements can streamline work flow to optimize efficiency and patient satisfaction.

Outcomes after Failed Pneumatic Retinopexy for Retinal Detachment.

PURPOSE: To provide visual and anatomic outcomes for patients with retinal detachment (RD) in whom primary pneumatic retinopexy (PR) failed. DESIGN: Retrospective, single-center, consecutive case series. PARTICIPANTS: Eyes with RD that failed a primary PR. METHODS: Anatomic and functional outcomes were evaluated for patients receiving treatment for failed PR. Three secondary procedures were compared, including repeat PR, pars plana vitrectomy (PPV), and combined scleral buckle (SB) plus PPV (SB+PPV). MAIN OUTCOME MEASURES: Anatomic reattachment and visual acuity (VA) at 1 year. RESULTS: Of a total of 423 primary PRs performed for RD, this study included 73 cases that failed. The overall single surgery anatomic success rate for the secondary procedure was 75%; the final success rate at 1 year was 100%. There was no statistically significant difference in success rates between repeat PR (63%), PPV (76%), and SB+PPV (88%). Improvement in VA was similar at 1 year between all 3 groups. Visual acuity at 1 year was similar between eyes undergoing PPV and SB+PPV (0.47 logMAR VA [Snellen equivalent, 20/59] for PPV and 0.52 logMAR VA [Snellen equivalent, 20/66] for SB+PPV; P = 0.75). Visual acuity at 1 year was better for those without macular involvement at the time of secondary procedure compared with eyes whose maculae detached (0.29 logMAR VA [Snellen equivalent, 20/39] vs. 0.73 logMAR VA [Snellen equivalent, 20/106]; P < 0.005). Fifty percent of PR failures underwent a secondary procedure within 1 week of primary PR; 80% occurred within 1 month. CONCLUSIONS: Anatomic success rates for secondary PR, PPV, and SB+PPV after failed PR were lower than published success rates for their use in primary RD. This suggests that a failed primary PR selects for RDs that are inherently more difficult to reattach. There was a trend suggesting that anatomic success rates are greater with SB+PPV than PPV and, in turn, with PPV than repeat PR. However, these differences were not statistically significant and did not translate into better VA gains at 1 year for either procedure. The suitable procedure after failed PR thus depends on patient presentation, surgeon preference, and patient preference.

Lower conjunctival fornix packing for mydriasis in premature infants: a randomized trial.

OBJECTIVE: To compare the mydriatic effect of lower conjunctival fornix packing to conventional instillation of eyedrops containing 2.5% phenylephrine and 1% tropicamide in premature infants undergoing examination for retinopathy of prematurity. METHODS: The patients were randomized to receive either conventional instillation of mydriatic drops or lower conjunctival fornix packing in one eye and the alternate method in the fellow eye. For the eyes receiving lower conjunctival fornix packing (study group), one small piece of the cotton wool soaked with one drop of 2.5% phenylephrine and one drop of 1% tropicamide was packed in the lower conjunctival fornix for 15 minutes. For the eyes receiving the conventional instillation (control group), 2.5% phenylephrine and 1% tropicamide were alternately instilled every 5 minutes for two doses each. Horizontal pupil diameter was measured with a ruler in millimeters 40 minutes later. RESULTS: The mean dilated pupil diameter in study group and control group were 5.76 ± 1.01 mm and 4.50 ± 1.08 mm, respectively. This difference was statistically significant (P < 0.05). CONCLUSION: The dilated pupil diameter after receiving the lower conjunctival fornix packing was larger than conventional instillation with a statistically significant difference. We recommended the packing method to dilate the preterm infant pupil, especially if the pupil is difficult to dilate.

The impact of preprinted prescription forms on medication prescribing errors in an ophthalmology clinic in northeast Thailand: a non-randomised interventional study.

OBJECTIVES: To understand the incidence and types of medication prescribing errors in a low resource setting ophthalmology clinic and to determine the impact of a preprinted prescription based on the hospital formulary (FormularyScript) on medication prescribing errors. DESIGN: Non-randomised interventional study. SETTING: Ophthalmology clinic in a teaching hospital in northeast Thailand. PARTICIPANTS: 4349 handwritten prescriptions collected from October 2009 to December 2009, and 4146 FormularyScripts collected from February 2010 to May 2010. PRIMARY AND SECONDARY OUTCOME MEASURES: All prescriptions from the handwritten and FormularyScript groups were analysed for medication error rates by types (legibility, ambiguous, incomplete, abbreviation and accuracy) and subtypes (drug name, strength, which eye, route and dispensed amount). RESULTS: Comparison of error rates in the two groups showed a 10-fold reduction in the overall error rate using FormularyScript (32.9%-3.5%, p<0.001). FormularyScripts were associated with statistically significant (p<0.001) decreases in the following error types: legibility (16.1%-0.1%), incomplete (16.1%-0.1%) and abbreviation (3.1%-0.3%). There was no statistically significant change in accuracy errors (0.8%-0.6%, p=0.21). Ambiguous errors increased with FormularyScripts (0.6%-2.5%, p<0.001), likely due to the introduction of new ways to make errors. Decreases were seen in all legibility, abbreviation and accuracy error subtypes, and four out of six incomplete error subtypes. There were statistically significant increases in both ambiguous error subtypes: which eye (0.3%-2.5%, p<0.001) and drug name (0.3%-0.6%, p=0.03). CONCLUSIONS: In our study population, outpatient medication prescribing errors were common and primarily due to legibility and incomplete error types. A preprinted prescription form has the potential to decrease medication prescribing errors related to legibility, incomplete prescribing information and use of unacceptable abbreviations without changing the overall rate of accuracy errors. However, new error types can occur.

Blast eye injuries: a review for first responders.

As the rate of terrorism increases, it is important for health care providers to become familiar with the management of injuries inflicted by blasts and explosions. This article reviews the ocular injuries associated with explosive blasts, providing basic concepts with which to approach the blast-injured patient with eye trauma. We conducted a literature review of relevant articles indexed in PubMed between 1948 and 2007. Two hundred forty-four articles were reviewed. We concluded that ocular injury is a frequent cause of morbidity in blast victims, occurring in up to 28% of blast survivors. Secondary blast injuries, resulting from flying fragments and debris, cause the majority of eye injuries among blast victims. The most common blast eye injuries include corneal abrasions and foreign bodies, eyelid lacerations, open globe injuries, and intraocular foreign bodies. Injuries to the periorbital area can be a source of significant morbidity, and ocular blast injuries have the potential to result in severe vision loss.

Treatment of acute retinal necrosis.

OBJECTIVES: To compare outcomes from patients with acute retinal necrosis (ARN) treated in the acyclovir-only era with those treated in the era of newer antiviral therapies, identify variables affecting outcomes in ARN, and evaluate strategies for fellow eye prophylaxis. DESIGN: Multicenter, nonrandomized, retrospective, interventional series. PARTICIPANTS: A cohort of 58 patients diagnosed with ARN by a retina specialist at 1 of 4 referral centers between 1981 and 2008. The cohort was divided into 2 subgroups: patients treated during the acyclovir-only era (n = 36) and patients treated during the current era of newer antiviral medications (n = 22). INTERVENTION: Intravenous, oral, or intravitreal antiviral medications, including acyclovir, valacyclovir, famciclovir, valganciclovir, ganciclovir, and foscarnet; prophylactic laser retinopexy; aspirin; oral steroids. MAIN OUTCOME MEASURES: Visual acuity, retinal detachment, and fellow eye involvement. RESULTS: A wide range and combination of antiviral agents are currently used for initial and long-term treatment of ARN. Outcomes from the newer antivirals era were similar to those achieved during the acyclovir-only era. In both groups, the incidence of 20/200 or worse visual acuity was 24% per person-year (P = 0.91). The prevalence of retinal detachment was approximately 50% in each group (P = 0.59). No variables, including prophylactic laser retinopexy, were associated with risk of retinal detachment. Two patients (3.4%) developed ARN in the initially unaffected eye. CONCLUSIONS: Current treatment trends vary widely, including single agents or combinations of oral, intravenous, and intravitreal agents. Differing strategies did not affect outcomes. The final visual acuity in ARN was generally poor. Retinal detachment was common and could neither be predicted nor prevented. Development of ARN in the unaffected fellow eye occurred rarely. Long-term oral antiviral treatment strategies varied with unclear relative efficacy. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

Effects of ranibizumab on exudative disciform scars.

BACKGROUND AND OBJECTIVE: To evaluate the effect of intravitreal ranibizumab in patients with leaking disciform scars. PATIENTS AND METHODS: In this retrospective case series, 31 eyes received one or two ranibizumab injections for treatment of choroidal neovascularization. Visual acuity, central retinal thickness, and macular volume were measured prior to injection and at 1-month follow-up. RESULTS: After one injection (n = 31), mean optical coherence tomography (OCT) central foveal thickness decreased from 317 to 242 microm (P = .00016). Mean OCT macular volume decreased from 7.89 to 6.80 mm3 (P = .00019). After two injections (n = 12), mean OCT central foveal thickness decreased from 310 to 248 microm following the second injection (P = .04). Mean OCT macular volume decreased from 7.80 to 6.43 mm3 at 1-month follow-up after a second injection (P = .006). There was no significant change in visual acuity after injections. CONCLUSION: In the short-term, ranibizumab decreases the leakage associated with choroidal neovascularization in chronic macular degeneration.

Array element localization using ship noise.

This paper describes a method of estimating hydrophone positions in a receiver array using the noise from a passing ship. Relative arrival times of the ship-noise signal between pairs of hydrophones are obtained from several time windows of data (corresponding to different ship locations) by cross-correlating the band-pass filtered time series. The relative arrival times are used as data in an array element localization inversion to estimate both the hydrophone and ship locations based on iterated linearization of the acoustic ray equations. The inversion applies the method of regularization to include prior information such as approximate location estimates and uncertainties for the source and receivers and the expectation that the array shape and or source tracks are smooth functions of position. Linearized and nonlinear (Monte Carlo) estimates of the position errors are in good agreement and indicate a high degree of confidence in the receiver positions (relative uncertainties of approximately 0.2 m in the horizontal and 0.05-0.1 m in the vertical). The ability to improve upon the initial source position estimates depends on the geometry of the problem, as investigated with simulations.