Management zones in transboundary aquifers: A review of delineation methods under a new framework of cross-border groundwater impacts.

Attention on the use of transboundary aquifers (TBAs) and their cross-border impacts is growing as countries become increasingly concerned about their long-term water security. Cross-border impacts, in groundwater quality and quantity, tend to concentrate in specific parts of TBAs, as they largely depend on the transboundary flow dynamics where anthropogenic actions operate. Thus, there is a growing consensus that strategies intended to prevent or mitigate such impacts should be implemented in strategic zones rather than in the whole TBA. These transboundary groundwater management zones (TGMZs) are relatively recent but have become a prominent topic in TBA management. However, until now, limited effort has been put into exploring the concept of TGMZs and the methods for their delineation. This research aims to fill these gaps and provide a basis for the delineation of TGMZs, thus helping neighbouring countries meet international responsibilities regarding the right to use and enjoy groundwater in TBAs. By reviewing academic and grey literature accessible from public sources, we present an overview of the concept and terminology of TGMZs, the approaches proposed for their delineation, and current operating examples. Additionally, we build a conceptual framework for assessing cross-border groundwater impacts by identifying their typologies and causal factors. We then apply our framework to evaluate and compare three reported methods which identify and delineate TGMZs from distinct perspectives, thereby gaining insights into their principles, performances, and limitations. Finally, we provide recommendations for further research towards optimising methods for delineating TGMZs.

The variation in optical coherence tomography-measured macular thickness in diabetic eyes without clinical macular edema.

PURPOSE: To determine the variation in optical coherence tomography (OCT)-measured macular thickness in diabetic eyes without clinical edema and to investigate factors that might influence variation in macular thickness. DESIGN: Retrospective, observational case series from a clinical practice. METHODS: Review of clinical charts and longitudinal OCT measurements of a consecutive series of 56 eyes of 56 patients with diabetes but no clinical macular edema. Measured variables include OCT central subfield mean thickness (CSMT), total macular volume (TMV), and logarithm of the minimum angle of resolution (logMAR) visual acuity. RESULTS: Over a median follow-up of 17 months, interquartile range (IQR) (9, 23), the median variation in CSMT was 18 microns, IQR (11, 31), and the median variation in TMV was 0.09 mm(3), IQR (0.06, 0.16). Variation in CSMT did not change significantly with increasing CSMT. Absolute, but not relative, variation in TMV increased with increasing baseline values (P = .0127 and P = .1538 for absolute variation and relative variation in TMV, respectively). The variation in CSMT and TMV did not vary with follow-up time and did not vary with age, gender, race, hypertension status, glycosylated hemoglobin, or retinopathy level. CONCLUSIONS: Variation in CSMT and TMV in diabetic eyes without DME over intervals up to 17 months is no greater than OCT measurement variability in eyes without and with DME. A change in the OCT-measured macular thickness greater than 10% of the baseline thickness is likely to represent a true change in the macular thickness and not OCT measurement variability, diurnal variation, or variability occurring over longer time scales.

The relationship of macular thickness to clinically graded diabetic retinopathy severity in eyes without clinically detected diabetic macular edema.

PURPOSE: To examine the relationship of optical coherence tomography (OCT) measured macular thickness to retinopathy severity in patients with diabetes and no clinically detectable macular edema. DESIGN: Retrospective observational case series. PARTICIPANTS: Three hundred eighty-three eyes of 383 patients of a private retina practice; including 100 normal eyes of patients without diabetes, 100 eyes of diabetics without retinopathy, 100 eyes of diabetics with mild to moderate retinopathy, 35 eyes of diabetics with severe nonproliferative or proliferative retinopathy, and 48 eyes of diabetics with regressed proliferative retinopathy. METHODS: Review of clinical charts and optical coherence tomography measurements. MAIN OUTCOME MEASURES: Central subfield mean thickness (CSMT), inner and outer zone measurements, and total macular volume. RESULTS: Central subfield mean thicknesses (mean +/- standard deviation) were 208+/-22, 198+/-25, 204+/-26, 224+/-38, and 205+/-27 microm for normals, eyes of diabetics without retinopathy, eyes with mild to moderate nonproliferative retinopathy, eyes with severe nonproliferative to proliferative retinopathy, and eyes with regressed proliferative retinopathy, respectively. For all groups, mean CSMT was larger in males than in females. Statistically significant differences by gender were observed for normals, diabetics without retinopathy, and diabetics with mild to moderate nonproliferative retinopathy (mean differences, 12, 14, and 18 microm, respectively; Ps = 0.0057, 0.0057, and 0.0002). For increasing retinopathy severity, the probability of macular thickening detected by OCT but not detected by clinical examination increased. Fifteen percent of eyes with severe nonproliferative or proliferative retinopathy and no clinically detected edema had OCT-measured macular thickening. CONCLUSIONS: Because OCT measurements are gender dependent, gender balance or statistical adjustment for gender imbalances of compared groups in OCT studies of diabetic macular edema is important. As retinopathy severity increases, the probability of subclinical edema rises. Except for an individual baseline measurement possibly useful for longitudinal comparison, the data suggest that there is little reason routinely to obtain OCT in eyes with diabetes and no retinopathy or mild to moderate diabetic retinopathy when clinical examination fails to show macular edema.

The predictive value of patient and eye characteristics on the course of subclinical diabetic macular edema.

PURPOSE: To define the course of subclinical diabetic macular edema (DME) and identify any predictors of progression to clinically significant DME. DESIGN: Retrospective, observational case series. SETTING: Private retina practice. PATIENT POPULATION: One hundred and fifty-three eyes of 153 patients with diabetic retinopathy and subclinical DME. OBSERVATION PROCEDURES: Clinical charts review and longitudinal optical coherence tomography (OCT) measurements. MAIN OUTCOME MEASURES: Change in OCT values and time to eventual treatment for clinically significant DME. RESULTS: Over a median follow-up of 14 months (interquartile range, seven to 25 months), 48 of 153 eyes (31.4%) progressed to clinically significant DME. The numbers (%) of eyes showing decreased, unchanged, and increased central subfield mean thickness were 16 (10.5%), 117 (76.5%), and 20 (13.1%), respectively. None of the patients or eye variables typically assessed in clinical practice was predictive of progression from subclinical DME to clinically significant DME. CONCLUSIONS: Progression from subclinical DME to clinically significant DME may be detected by serial clinical and OCT assessment. Subclinical DME does not inexorably progress over time scales of one to two years, and a substantial fraction of eyes spontaneously improve. Follow-up intervals of four to six months allowed detection of progression to clinically significant DME. In this sample of patients, OCT did not help in predicting which eyes with subclinical DME would progress to clinically significant DME.

A spreadsheet template for the analysis of optical coherence tomography in the longitudinal management of diabetic macular edema.

BACKGROUND AND OBJECTIVE: To provide a tool for analyzing optical coherence tomography data in patients with diabetic macular edema. PATIENTS AND METHODS: Retrospective series of 206 patients with diabetic macular edema involving at least one eye and receiving focal laser photocoagulation, intravitreal triamcinolone acetonide injection, or vitrectomy, membrane peeling, and intravitreal triamcinolone acetonide injection, and of untreated fellow eyes without diabetic macular edema. Main outcome measures included foveal subfield mean thickness and thickening relative to normal (microns), total macular volume and its increase relative to normal (mm3), visual acuity (Snellen decimal), and intraocular pressure (mm Hg). RESULTS: The authors demonstrate a graphical display of data based on a spreadsheet template for the longitudinal management of diabetic macular edema. Complex relationships of ocular response and interventions are concisely displayed. CONCLUSION: A graphical display of optical coherence tomography, visual acuity, and intraocular pressure data is a practical aid in the management of diabetic macular edema.

Comparison of the magnitude and time course of macular thinning induced by different interventions for diabetic macular edema: implications for sequence of application.

PURPOSE: To determine estimates of the magnitude and time course of macular thinning induced by three interventions for diabetic macular edema (DME). DESIGN: Retrospective observational case series. PARTICIPANTS: Two hundred eleven eyes of 133 patients of a private retina practice, each diagnosed with DME in > or =1 eye. METHODS: Review of clinical charts and optical coherence tomography measurements of eyes receiving focal laser photocoagulation, intravitreal triamcinolone injection (IVTA), or vitrectomy compared to untreated fellow eyes without DME. MAIN OUTCOME MEASURES: Central subfield mean thickness (CSMT; in micrometers), total macular volume (cubic millimeters), visual acuity, and rates of increased macular thickening at follow-up. RESULTS: At 6 months follow-up, predicted change in CSMT is 0 mum for untreated fellow eyes without DME, -28 mum for eyes receiving focal laser, -83 mum for eyes receiving triamcinolone, and -92 mum for eyes receiving vitrectomy. The predicted change in Early Treatment Diabetic Retinopathy Study letters read at 6 months is 0 for untreated fellow eyes without DME, 0 for eyes receiving focal laser, +3 for eyes receiving IVTA, and -1 for eyes receiving vitrectomy. Increased thickening of the macula after interventions designed to thin it were 25.4% for focal laser, 3.8% for IVTA, and 19.0% for vitrectomy. CONCLUSIONS: Interventions for DME differ in effect size, durability of effects, and potential for subsequent increases in macular thickness. A prospective study to elucidate a preferred sequence of interventions in DME may be worthwhile.

Regional patterns of sight-threatening diabetic macular edema.

PURPOSE: To define regional patterns of macular thickening in diabetic macular edema (DME). DESIGN: Retrospective case series. SETTING: Retina practice. PATIENT POPULATION: Fifty-two normal eyes of 48 patients and 100 eyes of 80 patients with DME. EXPERIMENTAL PROCEDURE: We measured retinal thickness for nine zones and total macular volume using the 3.5-mm display of an optical coherence tomograph (OCT). We determined the normal ranges of values for zones, and then normal ranges of values for the difference in thickness between each pair of zones, termed comparisons. main outcome measures: Frequencies of increased zonal thickness, increased total macular volume, and abnormalities in zonal comparisons. RESULTS: We found the following abnormalities: increased total macular volume 49% (49/100), increased foveal zone thickness 46% (46/100), increased inner parafoveal zone thickness (average 42.2% for the four zones), and increased outer zone thickness (average 34.3% for the four zones). Abnormal two-zone comparisons were found in 1027 of the 7200 possible comparisons (14.3%). Of these abnormal comparisons, the fovea was thicker relative to another zone in 26%; the four inner parafoveal zones were thicker relative to other zones in 8.7% to 15.2% (average 13.0%); and the four outer zones were thicker relative to other zones in 3.9% to 7.6% (average 6%). Eighty-eight percent (88/100) of the eyes chosen on clinical grounds as needing focal laser photocoagulation were detected. CONCLUSION: A broader concept of OCT abnormality, which includes abnormalities in zonal relationships, may improve automated detection of DME compared with clinical judgment.

Ocular conditions associated with peripapillary subretinal neovascularization, their relative frequencies, and associated outcomes.

OBJECTIVE: To determine frequency and outcomes of conditions with peripapillary subretinal neovascular membranes (PSRNVMs). DESIGN: Retrospective observational case series. PARTICIPANTS: All patients from a private community-based retina practice diagnosed with a PSRNVM. METHODS: Review of clinical charts, photographs, and fluorescein angiograms of 115 eyes of 96 patients, accrued over 18 years. MAIN OUTCOME MEASURES: Demographics, visual acuity (VA), laterality, neovascular membrane type and recurrence status over treatment course, and associated ocular conditions. RESULTS: Prevalences of reported associations were 52 (45.2%), age-related maculopathy (ARM); 45 (39.1%), idiopathic; 5 (4.3%), multifocal choroiditis; 3 (2.6%), angioid streaks; 2 (1.7%), histoplasmosis; 2 (1.7%), choroidal osteoma; 1 (0.9%), optic disc drusen; and 1 (0.9%), congenital disc anomaly. Newly recognized associations include pattern dystrophy (3 [2.6%]) and peripapillary pseudopodal pigment epithelial and choroidal atrophy (1 [0.9%]). Second-eye involvement was observed in 19.8% of patients over a median follow-up of 2 years. Median initial VAs were 20/40 for ARM-associated eyes and 20/30 for idiopathic eyes (P = 0.0230). Median final VAs were 20/70 for ARM-associated eyes and 20/32 for idiopathic eyes (P = 0.0261). The VA changes in the ARM-associated and idiopathic groups did not differ significantly (P = 0.1453). Recurrence of PSRNVMs after laser ablation was seen in 14 of 73 eyes (19.2%). A case of a PSRNVM as a cause of pseudopapilledema leading to unnecessary neurological imaging is reported. CONCLUSIONS: Close inspection of fellow eyes at the time of first eye diagnosis and regular follow-up afterward are indicated, given the high rate of eventual bilateral involvement regardless of associated condition. Laser ablation of PSRNVMs with broad treatment margins reduces recurrence rates relative to earlier series. The differential diagnosis of disc edema should include PSRNVMs. Pattern dystrophy can be associated with PSRNVMs.

Clinical management of silicone intraocular lens condensation.

PURPOSE: To report a novel technique in the management of silicone intraocular lens condensation after gas-fluid exchange. DESIGN: Interventional case report. METHODS: Clinical management of an obstacle to treatment. setting: Private retina practice. patient population: One patient with silicone posterior chamber intraocular lens implant and posterior capsulotomy who subsequently experienced complicated retinal detachment. intervention: Application of a heating pad to clear intraocular lens condensation. main outcome measure: Visibility of the fundus for laser treatment. RESULTS: Application of a heating pad to the closed eyelid significantly reduced the intraocular lens condensation and provided a clear view for the surgeon to apply laser retinopexy. CONCLUSIONS: Treatment of retinal detachment is complicated by lens condensation after gas-fluid exchange in patients who have undergone silicone posterior chamber intraocular lens implantation and posterior capsulotomy. We report a simple, inexpensive, and effective method to reduce lens condensation and enable in-office examination and laser treatment.

Intraobserver variability in optical coherence tomography.

PURPOSE: To assess the intraobserver variability of optical coherence tomography (OCT) in patients with clinically stable maculas. DESIGN: Retrospective, observational case series using a diagnostic instrument. METHODS: Retrospective study. setting. Private retina practice. patient population. Twenty-two eyes of 19 patients, each studied twice within 4 months. observation procedure. Optical coherence tomograph measurements of the macula obtained by two photographers. main outcome measures. Ordinary least products (OLP) and Bland-Altman analysis of OCT data. RESULTS: No fixed or proportional bias was detected in foveal zone thickness and total macular volume between measurements of either of the OCT operators. The coefficient of repeatability for foveal zone thickness was 37.0 microm for photographer 1 and 34.8 microm for photographer 2. The coefficient of repeatability for total macular volume was 0.29 mm(3) for photographer 1 and 0.10 mm(3) for photographer 2. CONCLUSION: Foveal zone thickness and total macular volume measurements show low intraobserver variability when analyzed by OLP and Bland-Altman techniques. Bounds are given for foveal zone thickness and total macular volume for which longitudinal OCT measurements by the same operator can be considered to reflect natural history or intervention effects rather than intraobserver variability.

Retinal vein occlusions in patients taking warfarin.

OBJECTIVE: To describe development of retinal vein occlusion (RVO) in patients anticoagulated with warfarin. DESIGN: Retrospective, observational case series. PARTICIPANTS: Thirteen patients drawn from a private retina practice. METHODS: Review of clinical records, laboratory results, color fundus photographs, and fluorescein angiograms. MAIN OUTCOME MEASURES: Primary measures were international normalized ratio (INR), visual acuity, and concurrent systemic disease. RESULTS: The female-to-male ratio was 7 to 6. Age range was 44 to 86 years, with a median age of 73 years. Two patients had systemic lupus erythematosus, 7 had hypertension, and 2 had primary open-angle glaucoma. Two had laboratory abnormalities: 1 with a combination of lupus anticoagulant and anticardiolipin antibodies and 1 with a combination of hyperhomocystinemia and low antithrombin III. Three patients were taking acetylsalicylic acid in addition to warfarin at the time of the RVO. The INRs at the time of RVO were 0.9 to 3.8, with 9 of 13 <==2.0. CONCLUSIONS: Anticoagulation with warfarin does not preclude RVO in predisposed patients, nor does combination therapy with warfarin and acetylsalicylic acid. Attention to keeping the INR >2.0 may be helpful.

Optical coherence tomography to detect macular edema in the presence of asteroid hyalosis.

PURPOSE: To propose the use of optical coherence tomography as an effective diagnostic tool for identifying macular edema in patients with asteroid hyalosis obscuring the fundus view. DESIGN: Case report. METHODS: Review of clinical chart and images. SETTING: Private retina practice. PATIENT: One patient diagnosed with diabetic retinopathy and asteroid hyalosis, who was experiencing decreased visual acuity and whose fundus view was inadequate for diagnosis using customary techniques. RESULTS: Usual methods of diagnosis were ineffective until OCT obtained a clear image of the fundus and subsequent macular thickening with vitreomacular adhesion. CONCLUSIONS: Optical coherence tomography is an effective diagnostic tool for discovering macular edema in cases of dense asteroid hyalosis where traditional methods fail to obtain a clear image of the fundus.