Prevalence of asymptomatic Plasmodium infections with sub-microscopic parasite densities in the northwestern border of Thailand: a potential threat to malaria elimination.

BACKGROUND: Asymptomatic infections with sub-microscopic Plasmodium serve as a silent reservoir of disease, critical to sustaining a low level of remanent malaria in the population. These infections must be effectively identified and targeted for elimination. The sensitivity of light microscopy, the traditional method used for diagnosing Plasmodium infections, is frequently insufficient for detecting asymptomatic infections due to the low density of parasitaemia. The objective of this study was to explore the current prevalence of asymptomatic sub-microscopic Plasmodium carriages to evaluate the parasite reservoir amongst residents from 7 hamlets in Tak Province in northwestern Thailand using a highly sensitive molecular method. METHODS: Malaria infection was screened in a real-world setting from 3650 finger-prick blood specimens collected in a mass cross-sectional survey using light microscopy and loop-mediated isothermal amplification (LAMP). LAMP results were later confirmed in a laboratory setting in Bangkok using nested PCR, restriction enzyme digestion and DNA sequencing. The association of malaria infection with demographic factors was explored. RESULTS: Parasite prevalence was 0.27% (10/3650) as determined by microscopy. Sub-microscopic infection prevalence was 2.33% (85/3650) by LAMP. Of these, 30.6% (26/85) were infected with Plasmodium falciparum, 52.9% (45/85) with Plasmodium vivax, 2.4% (2/85) with Plasmodium malariae, 4.7% (4/85) with mixed P. falciparum and P. vivax, and 9.4% (8/85) had parasite densities too low for species identification. Asymptomatic carriages (T < 37.5 °C) accounted for 95% (76/80) of all sub-microscopic cases with the highest prevalence occurring in the subjects 31-45 years of age (p ≤ 0.035). Participants working on plantations or as merchants had an increased infection risk. Evaluation by microscopy identified 10.53% (10/95) of all Plasmodium infected participants. CONCLUSION: Participants carrying asymptomatic Plasmodium infections with sub-microscopic parasite densities are considerable in this area. These findings provide the true disease burden and risk factors in this region. This information helps to direct policy makers towards better schemes and delivery of targeted interventions. Moreover, this is the first study to use LAMP in mass screening for sub-clinical and sub-microscopic infections in a field setting in Thailand. LAMP proves to be a sensitive and field-deployable assay suitable for national malaria control screening campaigns.

Movement of the ß-hairpin in the third zinc-binding module of UvrA is required for DNA damage recognition.

Nucleotide excision repair (NER) is distinguished from other DNA repair pathways by its ability to process various DNA lesions. In bacterial NER, UvrA is the key protein that detects damage and initiates the downstream NER cascade. Although it is known that UvrA preferentially binds to damaged DNA, the mechanism for damage recognition is unclear. A ß-hairpin in the third Zn-binding module (Zn3hp) of UvrA has been suggested to undergo a conformational change upon DNA binding, and proposed to be important for damage sensing. Here, we investigate the contribution of the dynamics in the Zn3hp structural element to various activities of UvrA during the early steps of NER. By restricting the movement of the Zn3hp using disulfide crosslinking, we showed that the movement of the Zn3hp is required for damage-specific binding, UvrB loading and ATPase activities of UvrA. We individually inactivated each of the nucleotide binding sites in UvrA to investigate its role in the movement of the Zn3hp. Our results suggest that the conformational change of the Zn3hp is controlled by ATP hydrolysis at the distal nucleotide binding site. We propose a bi-phasic damage inspection model of UvrA in which movement of the Zn3hp plays a key role in damage recognition.

Clinical Implications of Preformed Archwire Selection on the Treatment of Angle Class I/II division 1 Malocclusions in Thais.

INTRODUCTION: The dental arch forms were compared of untreated Class I and Class II div 1 malocclusions to those of non-customized preformed archwires manufactured by American Orthodontics, G&H, Highland, Ormco, RMO, and 3MUnitek. Arch forms of post-treatment Class II div 1 malocclusions treated by four 1st premolar extractions are also compared. MATERIALS AND METHODS: Four metrics of archform shape and size (canine and 1(st) molar depth and inter-canine and inter 1(st) molar width) were measured on dental casts of 40 Class I and 22 Class II div 1 patients. These same metrics were also used to describe preformed archwire forms. RESULTS: Non-customized preformed wires all showed significantly narrowed mandibular arch forms. This was true for maxillary archwires, with four exceptions. The Highland Natural Arch form, G&H True form I, and RMO natural preformed archwires showed both inter-canine and 1(st) molar widths statistically the same as mean dental arch widths in both the untreated and post-treatment Class II groups. In Class I patients, these three archwires showed only inter-canine widths equivalent to dental measurements. The Highland Progressive archwire matched only the 1(st) molar width in the untreated Class II group. CONCLUSION: None of these archwires - if used unadjusted, will produce a significant expansive force in either the maxillary or mandibular arch. Three maxillary non-customized preformed archwires showed both inter-canine and 1(st) molar arch widths statistically the same as Thai Class II div 1 dental arch dimensions. Using them to treat this malocclusion should minimally affect both pre and post-treatment maxillary arch form.

A comparison of vestibular evoked myogenic potential (VEMP) between definite Meniere's disease patients and normal healthy adults.

OBJECTIVE: To compare the results of VEMP between unilateral definite Meniere's disease patients and normal healthy adults. MATERIAL AND METHOD: Thirty-two patients with unilateral definite Meniere's disease patients and 32 age-matched normal healthy adults (control) underwent VEMP tests with short tone burst of 500 Hz at 90 dBnHL. Student-t test was used for comparison of means of all parameters between two groups. RESULTS: Absent VEMP response was found in 14 MD patients and abnormal asymmetry ratio (AR) was found in five MD patients. Normal responses were found in all subjects of the control group. The mean P1 and N1 latencies, VEMP amplitude between unilateral MD, and control were not significantly different between two groups. However the difference between the mean AR of both groups showed statistically significant (p-value < 0.05). The upper limit of normal AR was calculated to be of 35.15%. CONCLUSION: The absence of VEMP response and AR of VEMP were more dominant than other parameters such as P1 and N1 latencies or VEMP amplitude in the detection of saccular dysfunction in MD. The results suggested that AR should be used as a tool in interpretation of VEMP response for the diagnostic batteries in MD. The upper limit of normal AR of < or = 35% should be recommended.

Reliability of visual acuity measurements taken with a notebook and a tablet computer in participants who were illiterate to Roman characters.

BACKGROUND: Electronic measurement of visual acuity (VA) has been proposed and adopted as a method of determining VA scores in clinical research. Characters (optotypes) are displayed on a monitor screen and the examinee selects a match and inputs his choice to another electronic device. Unfortunately, the optotypes, called Sloan letters, in the standard protocol are 10 Roman characters. This limits their practicabilityfor measuring VA of patients who are illiterate to these characters. The authors introduced a method of displaying the Sloan letters one by one on a notebook and all 10 Sloan letters on a tablet computer screen. The former is for testing the patients whereas the latter is for them to input their responses by tapping on a letter that matches the one on the notebook screen. OBJECTIVE: To assess test-retest reliability of VA scores determined with this method. MATERIAL AND METHOD: Participants without ocular abnormality were recruited to have their right eyes measured with the same VA measurement method twice, one week apart. Those who were illiterate to Roman characters were enrolled for the aforementioned method for measuring their VA (Tablet group). A 15-inch display notebook computer and a 9-inch display tablet computer (iPad) communicated via a local wireless data network provided by a Wi-Fi router. Those who understood Roman characters were enrolled to have measurements with a 17-inch desktop computer and an infrared wireless keyboard (Keyboard group). Both methods used the same protocols and software for VA measurements. Reliability of VA scores obtained from each group was assessed by the confidence interval (CI) of the difference of the scores from the test and retest. The t test was used to analyze differences in mean VA scores between the test and retest in each group with p < 0.05 determined as statistically significant. RESULTS: There were 49 and 50 participants in the Tablet and Keyboard group respectively. The 95% CI of the difference between the scores from the test and retest in each group was 2 letters. Approximately 95% of participants in each group had an absolute difference of the scores between the test and retest of 7 letters. The mean of VA scores from the first test was significantly different from that of the second test in the Keyboard group (one-letter difference, p = 0.049); there was no significant difference between these scores in the Tablet group (0.1-letter difference, p = 0.86). CONCLUSION: Tablet computers may be used to assist patients who are illiterate to Roman characters in having their VA measured with the standard electronic protocol. This preliminary study suggested that the proposed method should be useful for reliable measuring VA outcome in multicenter international clinical trials without encountering a language barrier

Major single nucleotide polymorphisms in polypoidal choroidal vasculopathy: a comparative analysis between Thai and other Asian populations.

PURPOSE: To investigate the association in a Thai population between the major age-related macular degeneration (AMD) susceptibility loci, Y402H and I62V in the complement factor H (CFH) and A69S in the age-related maculopathy susceptibility 2 (ARMS2) genes, and polypoidal choroidal vasculopathy (PCV). METHODS: A case-control study included 97 PCV cases and 102 age- and gender-matched controls without any retinopathy. The genotypic profiles of the three polymorphisms were obtained using a real-time polymerase chain reaction assay. The allelic and genotypic association between the polymorphisms and PCV were compared with those from the compiled data of other Asian populations reported previously. RESULTS: Strong associations between the Y402H, I62V, and A69S polymorphisms and PCV were observed in the present study (P = 0.002, 0.003, and 0.0008 respectively) and in the compiled data (P < 0.0001 for all three polymorphisms). The risk allele frequencies of the polymorphisms in PCVs and in controls from the present study (15.0% and 5.4% for Y402H, 71.7% and 57.4% for I62V, and 54.1% and 37.3% for A69S respectively) were also comparable with the frequencies from the compiled data (10.3% and 6.4% for Y402H, 75.2% and 58.3% for I62V, and 56.8% and 36.8% for A69S respectively). The genotype distribution for each polymorphism was also comparable in both datasets. CONCLUSION: The findings of this study support a significant genetic association between the major AMD susceptibility genes and PCV across Asian populations. This suggests that AMD and PCV, despite different phenotypic manifestation, may share common genetic risk factors.

Intramyocardial angiogenic cell precursors in nonischemic dilated cardiomyopathy.

To determine the efficacy of intramyocardial injection of angiogenic cell precursors in nonischemic dilated cardiomyopathy, 35 patients with nonischemic dilated cardiomyopathy underwent injections of angiogenic cell precursors into the left ventricle (cell group). Seventeen patients with nonischemic dilated cardiomyopathy were matched from the heart failure database to form a control group that was treated medically. Angiogenic cell precursors were obtained from autologous blood, cultured in vitro, and injected into all free-wall areas of the left ventricle in the cell group. After these injections, New York Heart Association functional class improved significantly by 1.1 +/- 0.7 classes at 284.7 +/- 136.2 days, and left ventricular ejection fraction improved in 71.4% of patients (25/35); the mean increase in left ventricular ejection fraction was 4.4% +/- 10.6% at 192.7 +/- 135.1 days. Improved quality of life was demonstrated by better physical function, role-physical, general health, and vitality domains in a short-form health survey at the 3-month follow-up. In the control group, there were no significant improvements in left ventricular ejection fraction or New York Heart Association class which increased by 0.6 +/- 0.8 classes. It was concluded that intramyocardial angiogenic cell precursor injection is probably effective in the treatment of nonischemic dilated cardiomyopathy.

Genotypic resistance profiles in antiretroviral-naive HIV-1 infections before and after initiation of first-line HAART: impact of polymorphism on resistance to therapy.

Genotypic testing using TRUGENE was performed for treatment-naive, human immunodeficiency virus type 1 (HIV-1)-infected patients at baseline and after initiation of protease inhibitor (PI)-based highly active antiretroviral therapy (HAART) regimens. The genetic diversity of HIV-1 pol sequences from 92 CRF01_AE and 21 B strains was compared. Subsequently, the impact of polymorphism on resistance to therapy was studied in CRF01_AE-infected (n=29) and subtype B-infected (n=14) patients. At baseline, the differences between CRF01_AE and B strain were mainly observed in the minor mutations L10I/V, M36I and L63P/I/H (P<0.001, chi(2)). In the reverse transcriptase sequence, M41L and T215Y/S were more common in patients infected with subtype B virus (P<0.05, chi(2)). Although all patients treated with PI-based HAART had pre-existing minor mutations, a low prevalence of resistance to PIs was observed (5/43; 11.6%). Moreover, major mutations (D30N and N88D) conferring resistance to PIs were found in patients infected with subtype B strain. In conclusion, polymorphisms at the protease region may not reduce PI susceptibility during treatment. However, this study also revealed the difference in natural mutations among subtypes, which may affect the manifestation of drug resistance.

The relationship between bone and ash weight to body weight and body length of Thai corpses in Bangkok and central part of Thailand after cremation.

BACKGROUND: Although information about bone and ash weight compare to body weight and body length of Thai people exists, it was based on a few samples. OBJECTIVE: Collect data of the bone and ash weight after cremation and find out the relationship between bone and ash weight, body weight, body length, and age. MATERIAL AND METHOD: Two hundred and twenty three corpses, 97 females and 126 males were collected from four temples, three temples from Bangkok and one temple from Angtong province. The crematoria used in the present study created a temperature between 850 degrees C and 1,200 degrees C. Each cremation took about 1-1.5 hours. RESULTS: The average with SD of bone and ash weight of males was 2.44 kg +/- 0.9 Kg, while the weight of females was 2.07 +/- 0.89 Kg, and the average of bone and ash weight of total subjects was 2.28 +/- 0.95. There was negative correlation between age and bone & ash weight, while there was positive correlation between body length and body weight, body length and bone & ash weight, and body weight and bone & ash weight. The results of the present study indicated that age and body weight affected the bone and ash weight. The fitted linear equation was Log (bone & ash weight +1) = 0.413 - 0.001 (age) + 0.003 (body weight). CONCLUSION: Age and body weight affect bone and ash weight. Moreover, the age, body weight, and body length could be estimated by using the bone and ash weight.

Genotypic resistance mutations in treatment-naïve and treatment-experienced patients under widespread use of antiretroviral drugs in Thailand: implications for further epidemiologic surveillance.

The aims of this study were to illustrate the prevalence and determinants of mutations associated with antiretroviral drug resistance in a group of antiretroviral-naive and treatment-experienced patients in Thailand, where antiretroviral drugs are widely used. One hundred and thirteen treatment-naive (92 CRF01_AE and 21 subtype B patients) and 1,709 treatment-experienced patients were recruited. Genotypic resistance to antiretroviral drugs was studied by sequencing the isolated viruses. Mutation frequencies in treatment-naive patients were reported along with those for treatment-experienced patients. The results showed that all of the patients with treatment-experienced patients showed the same pattern of genotypic resistance. The results also showed that only 14 drug-naive patients (12.4%) carried HIV-1, with at least one drug-resistant mutation. Moreover, four drug-naive patients were found to carry the marker mutations for transmission of drug resistance. The most commonly found marker in drug-naive patients was M36I/V/L (n=90, 81.1%), which is a common natural polymorphism among HIV-1 subtype CRF01_AE individuals. In order to prevent the rapid emergence of resistant virus strains, a national program to monitor antiretroviral drug resistance should be established. We also recommend routine genotypic testing in treatment-naive patients before starting antiretroviral therapy to prevent subtherapeutic response and viral failure.

Normal internal organ weight of Thai adults correlated to body length and body weight.

OBJECTIVE: Examine the relationship between the internal organ weight with body weight and body length. MATERIAL AND METHOD: Analysis of data from 250 autopsies from the Ramathibodi Hospital from August 2003 to February 2005. The cases were from sudden unnatural death including accident, homicide and suicide and excluded decomposed bodies, fire related deaths and cases where medical treatment had been given. The age ranged from 15 to 88 years and there were 51 females and 199 males. Parson's correlation coefficient was used to examine the relationship between the internal organ weight with body weight and body length. RESULTS: The mean+/-standard deviation (SD) were represented by males and females respectively; Brain 1339+/-160/1165+/-184 gm, heart 311+/-66/278+/-160 gm, lung 910+/-347/675+/-255 gm, liver 1439+/-365/ 1214+/-275 gm, spleen 103+/-46/92.9+/-48 gm, kidney 260+/-68/230+/-42 gm. CONCLUSION: The relationship between internal organ weight and body weight showed each internal organ significantly correlated with body weight in males at p-value < 0.05, whereas in females it only correlated to liver, kidney and spleen at p-value < 0.05. For the correlation between internal organ weight and body length, it showed only brain, lung, liver and kidney correlated to the body length in males at p-value < 0. 05, but not in females.

Interobserver agreement in the interpretation of single-field digital fundus images for diabetic retinopathy screening.

PURPOSE: To assess agreement among a group of ophthalmic care providers, including ophthalmologists and trained nonphysician personnel, in the interpretation of single-field digital fundus images for diabetic retinopathy screening. DESIGN: Interobserver reliability study. PARTICIPANTS: Twelve ophthalmic care personnel, including 3 retina specialists, 3 general ophthalmologists, 3 ophthalmic nurses, and 3 ophthalmic photographers. METHODS: All participants were to read 400 good single-field digital fundus images of diabetic patients from a community hospital. The nonphysician personnel group read the images 1 month after attending a 2-day intensive instruction course regarding diabetic retinopathy screening. The ophthalmologists read the images without additional training. The 3 retina specialists read the images again together 2 months later to form a consensus regarding retinopathy severity and macular edema for each case. All readers used the Early Treatment Diabetic Retinopathy Study standard photographs as guidelines. MAIN OUTCOME MEASURES: The kappa statistic was used for the reliability assessment of the diabetic retinopathy severity and macular edema, and for the identification of cases that needed referral to ophthalmologists. RESULTS: There is only fair agreement among all readers. The multirater kappa coefficient for retinopathy severity is 0.34; for macular edema, 0.27; and for referral cases, 0.28. Retina specialists have the best agreement among all groups (kappa = 0.58 for retinopathy severity or macular edema, kappa = 0.63 for referrals). There is also fair agreement when all readers are compared with the consensus of retina specialists (kappas = 0.35, 0.28, and 0.29 for retinopathy severity, macular edema, and referrals, respectively), and the retina specialist group also has the best agreement (kappas = 0.63, 0.65, and 0.67 for retinopathy severity, macular edema, and referrals). CONCLUSIONS: Without additional training, retina specialists may be the most reliable personnel to interpret single-field digital fundus images for diabetic retinopathy screening. For other ophthalmic care personnel to achieve comparable reliability, a comprehensive instruction course with specific continuing education is essential. Authorized nonphysician interpreters should be experts, and new standard photographs for single-field digital fundus image interpretation may also be required to improve interobserver reliability.

Relationship between bone and ash weight to age, body weight and body length of thai adults after cremation.

BACKGROUND: Cremation is the most common Thai funeral mode. In Thailand, there have not been any previous reports of bone and ash weight after cremation. OBJECTIVE: Collect the bone and ash weight after the cremation and find the variables that affected the bone and ash weight. MATERIAL AND METHOD: One hundred and ten samples, including fifty-five males and fifty-five females, were collected from the Thai population. A Thai crematorium (Series Tiger 1) that could produce a temperature of approximately 850 degrees C - 1200 degrees C was employed. It took about 1-1.5 hours to complete the incineration. RESULTS: The average bone and ash weight of the males was 2.68 kg with SD 1.41; female was 2.12 with SD 1.25; and total was 2.40 with SD 1.36. The present study supported that age and body weight affected the bone and ash weight while the body length (height) did not. The fitted equation was y = 1.969 - 0.01846 (age) + 0.03087 (body weight), where y = predicted bone and ash weight. CONCLUSION: The present study shows that age and body weight affected the bone and ash weight. From this information, the authors could find the predicted value of either age or body weight. If the authors would like to find the age, the authors can employ the fittest equation y = 76.097 - 3.219 (Bone and ash weight) where y = predicted age. Additionally, if the authors would like tofind the body weight, we can employ thefittest equation = 51.930 + 1.673 (Bone and ash weight) where y = predicted body weight.

Screening for diabetic retinopathy in rural area using single-field, digital fundus images.

OBJECTIVE: To evaluate the practicability of using single-field, 2.3 million-pixel, digital fundus images for screening of diabetic retinopathy in rural areas. MATERIAL AND METHOD: All diabetic patients who regularly attended the diabetic clinic at Kabcheang Community Hospital, located at 15 kilometers from the Thailand-Cambodia border, were appointed to the hospital for a 3-day diabetic retinopathy screening programme. The fundi of all patients were captured in single-field, 45 degrees, 2.3 million-pixel images using nonmydriatic digital fundus camera and then sent to a reading center in Bangkok. The fundi were also examined through dilated pupils by a retinal specialist at this hospital. The grading of diabetic retinopathy from two methods was compared for an exact agreement. RESULTS: The average duration of single digital fundus image capture was 2 minutes. The average file size of each image was 750 kilobytes. The average duration of single image transmission to a reading center in Bangkok via satellite was 3 minutes; via a conventional telephone line was 8 minutes. Of all 150 patients, 130 were assessed for an agreement between dilated fundus examination and digital fundus images in diagnosis of diabetic retinopathy. The exact agreement was 0.87, the weighted kappa statistics was 0.74. The sensitivity of digital fundus images in detecting diabetic retinopathy was 80%, the specificity was 96%. For diabetic macular edema the exact agreement was 0.97, the weighted kappa was 0.43, the sensitivity was 43%, and the specificity was 100%. CONCLUSION: The image capture of the nonmydriatic digital fundus camera is suitable for screening of diabetic retinopathy and single-field digital fundus images are potentially acceptable tools for the screening. The real-time image transmission via telephone lines to remote reading center, however, may not be practical for routine diabetic retinopathy screening in rural areas.

Water quality and breeding habitats of anopheline mosquito in northwestern Thailand.

Malaria transmission is dependent upon many hydrology-driven ecological factors that directly affect the vectorial competence, including the presence of suitable habitats for the development of anopheline larvae. Larval habitats were identified and characterized at three malaria endemic villages (Ban Khun Huay, Ban Pa Dae, and Ban Tham Seau) in Mae Sot district, Tak Province, in northwestern Thailand between July 2002 and June 2003. The Global Positioning System (GPS) was used to provide precise locational data for the spatial distribution of anopheline mosquito larvae and their habitats. Ten habitat categories were identified. Eighteen adult Anopheles species were identified from larvae in all the surveyed habitats. An. minimus was the most common species throughout the year. The relationship between eight abiotic variables (temperature, hardness, carbon dioxide, dissolved oxygen, nitrate, phosphate, silica and pH) and the abundance of four major species of malaria vectors (An. (Cel.) dirus, An. (Cel.) minimus, An. (Cel.) maculatus, and An. (Cel.) sawadwongporni), and six species of non-vectors (An. (Cel.) kochi, An. (Cel.) jamesii, An. (Ano.) peditaeniatus, An. (Ano.) barbirostris, An. (Ano.) campestris, and An (Cel.) vagus) larvae was investigated. The results from the multiple regression models suggest that hardness, water temperature and carbon dioxide are the best predictor variables associated with the abundance of An. minimus larvae (p < 0.001); water pH for An. dirus larvae (p < 0.001); temperature and pH for An. kochi larvae (p < 0.01); temperature and silica concentration for An. jamesii larvae (p < 0.001); dissolved oxygen and silica concentration for An. campestris larvae (p < 0.001); and pH and silica concentration for An. vagus larvae (p < 0.001). We could not identify key environmental variables for An. maculatus, An. sawadwongporni, An. peditaeniatus, and An. barbirostris.

Application of log-linear models to cancer patients: a case study of data from the National Cancer Institute.

Cancer is a noninfectious disease which is on the increase throughout the world and has become a serious problem for public health in many countries, including Thailand. In Thailand, cancer has risen significantly to become a leading cause of death and most patients are admitted to the National Cancer Institute. The objective of this study is to identify the associated factors between personal, cancer/clinical variables of cancer patients using log-linear models. Tests of independence are used (chi-square and Cramer's V-value tests) to find out the relationships between any two variables. In addition two- and three-dimensional log-linear models are used to obtain estimated parameters and expected frequencies for these models. Amongst the models fitted, the best are chosen based on the analysis of deviance. The results of this study show that most paired variables of personal, cancer/clinical variables are significantly related at p-value <0.05. For both male and female patients, the variable site of the cancer is highly related to marital status, diagnostic evidence and treatment, which provide the highest Cramer's V value. Moreover, the site of cancer also affects the method of diagnostic evidence and treatment. Since the site of cancer in each sex is different, prevention for various sites of cancer should be considered for each specific sex. In addition, for male and female patients, treatment is related to the site of cancer. Consequently, physicians may consider these factors before selecting the appropriate method of treatment.

Repeatability of an automated Landolt C test, compared with the early treatment of diabetic retinopathy study (ETDRS) chart testing.

PURPOSE: To evaluate the repeatability of visual acuity scores from the automated test and compare them with the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart. DESIGN: Instrument validation study based on a model of repeatability study in two observations. SMETHODS: a prospective, clinic-based, comparative study. A total of 206 participants without ocular diseases and refractive errors in their right eyes were randomly enrolled in the automated group in which 107 participants performed the automated test and the ETDRS group in which 99 participants read the ETDRS chart. All participants were tested with only their right eyes without corrections at 4 meters and came back to have the same tests 1 week later. The automated test used the Landolt rings as optotypes and was conducted by a low-ended personal computer with a 15-inch monitor and a wireless keyboard. The "letter" score calculated by counting every correct response to optotypes, and the "threshold curve" score interpreted from the optotype size at the midpoint of a visual acuity threshold curve. RESULTS: The 95% confidence interval of test-retest of visual acuity scores from the automated test are comparable to the ETDRS chart (.143 compared with.125 for letter scores,.145 compared with.122 for threshold curve scores). The score repeatabilities, calculated from the standard deviations of test-retest, from the automated test are also comparable to the ETDRS chart (.201 compared with.177 for letter scores,.206 compared with.172 for threshold curve scores). All comparisons demonstrated no statistical difference (P >.05). CONCLUSIONS: The automated testing system in this study enables practical measuring visual acuity by the Landolt rings. The system's repeatability, which is comparable to the ETDRS chart, supports its role as an alternative tool for measuring outcome in new clinical research. Its ability to practically generate visual acuity threshold curves may also be useful in future clinical research studies.

The Thai logarithmic visual acuity chart.

OBJECTIVE: To evaluate visual acuity scores from the Thai and the standard logarithmic visual acuity chart. DESIGN: Comparative non-randomized clinical study. PARTICIPANTS AND METHOD: 153 subjects, calculated from sample size estimation, without any ocular disease and aged between 18 and 80 years old who could read English and at least 3 out of 5 letters of the largest line of both charts were enrolled to use only their right eyes to read the Thai and the standard logarithmic visual acuity chart without any refractive correction. 27 subjects came back for second measurements of visual acuity in the same manner as the first a week later. MAIN OUTCOME MEASUREMENT: The visual acuity scores were divided into the Snellen or the whole line score and the ETDRS or the letter-by-letter score. The former was compared by weighted Kappa and the latter was compared by the paired t-test. RESULTS: There was high agreement in weighted Kappa between the Snellen scores from the Thai and standard chart (k = 0.7375). There was also high agreement in weighted Kappa between the Snellen scores from the first and second reading of the Thai chart (k = 0.7304) and the standard chart (k = 0.7282). A high correlation was observed between the ETDRS scores from the Thai and standard charts (r = 0.947). Also there was a high correlation between the ETDRS scores of the first and second reading of both the Thai chart (r = 0.962) and the standard chart (r = 0.952). There was a significant difference between the ETDRS scores from the Thai and standard chart (p<0.0001). There was no significant difference between the ETDRS scores from the first and second reading of either the Thai chart (p = 0.794) or the standard chart (p = 0.62). CONCLUSION: The Snellen visual acuity score from the Thai chart is comparable to the standard chart. Although the ETDRS score from the Thai chart is different statistically from the standard chart, its test-retest variability tends to be low. This suggests the possibility of using the Thai chart for monitoring of the ETDRS score in research studies.