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Biomedical subjects

P Cho

Publications and source records attributed to P Cho.

At least 19 recordsLinked to original sources
PubMed2005

Contrasting mechanisms of regulating translation of specific Drosophila germline mRNAs at the level of 5'-cap structure binding.

Translational control is a key genetic regulatory mechanism underlying the initial establishment of the major spatial axes of the Drosophila embryo. Many translational control mechanisms target eIF4E (eukaryotic initiation factor 4E), an initiation factor that recognizes the 5'-cap structure of the mRNA. Cap recognition by eIF4E, in complex with eIF4G, is essential for recruitment of the mRNA to the small ribosomal subunit. One established mechanism for repressing translation involves eIF4E-binding proteins, which competitively inhibit the eIF4E-eIF4G interaction. Our group has uncovered a novel mechanism for repression in which an eIF4E cognate protein called d4EHP, which cannot bind eIF4G, binds to the 5'-cap structure of cad mRNA thus rendering it translationally inactive. These two related, but distinct, mechanisms are discussed and contrasted in this review.

Animals↗
PubMed2001

Clinical performance of polynomial lenses versus tri-curve lenses. I: initial comfort.

Twenty-two subjects were asked to wear custom-made polynomial back surface design rigid gas permeable (RGP) lenses and conventional tri-curve RGP lenses to compare the initial comfort provided by the two lens designs monocularly and binocularly. Polynomial lenses, based on tri-curve lens fittings, did not provide better initial comfort than tri-curve lenses. The results seem to indicate that an aspheric back surface alone may not play a very important role in the initial comfort of RGP lens wear. The method used to derive the specifications of the polynomial surface may, however, need further modifications to improve its accuracy.

Journal Article↗
PubMed2001

Clinical performance of polynomial lenses versus tri-curve lenses. II: ocular responses.

This study, which was a continuation of the previous one, aimed to determine the subjective and objective responses after wearing polynomial and tri-curve rigid gas permeable (RGP) lenses over a period of 6 months. Subjects were divided into two groups, each of which wore either one of these lens designs and 17 of 22 subjects completed the 6-month study. Subjective responses were assessed by a questionnaire while the objective responses including vision, contrast sensitivity, lens fitting and the corneal integrity, corneal thickness and endothelial cell morphology were assessed by the examiner. There were no significant differences in the subjective ratings, vision, contrast sensitivity and the lens fitting between the two groups. Except for the p-value (p) and the apical radius (r(o)) along the steepest meridian and the coefficient of variation in cell size in the inferior corneal endothelium, there were no significant changes in the palpebral aperture size, the p-value and r(o) along the flattest meridian, corneal thickness and the other endothelial cell variables after the 6-month study period. The poor success and high dropout rates of RGP lens wear in this study stress the importance and need for further investigations of such lenses.

Journal Article↗
PubMed2001

Topographical mapping and in-office modification in the management of an orthokeratology patient.

A 20-year-old female was fitted with rigid gas permeable (RGP) orthokeratology (ortho-k) lenses for overnight wear. Both lenses decentred nasally due to the tight fit of the alignment zone (AZ) and the peripheral zone (PZ). The AZ and PZ of both lenses were flattened using an in-office modification unit. Centration of the right lens improved but a small central island was also observed. The left lens still decentred nasally. Both findings indicated that the AZ and PZ of the right lens were too steep leading to 'lens vaulting' or excessive central clearance and inadequate tear exchange, respectively. The AZ and PZ of both lenses were flattened further using the modification unit and after the adjustment, both lenses centred well and the central island in the right eye was eliminated. This case demonstrates the usefulness of topographical corneal mapping and in-office modification of lenses in the management of ortho-k patients.

Journal Article↗
PubMed2001

Vision of low astigmats through thick and thin lathe-cut soft contact lenses.

Distance and near visual acuity of 13 low astigmats were determined in a double-masked experiment through thick and thin (centre thickness 0.12 mm and 0.06 mm, respectively) spherical lathe-cut soft lenses. For each lens type, distance and near LogMAR VA and over-refraction were assessed with different logMAR VA charts. For 70% of the subjects, the residual astigmatism was significantly lower than the refractive astigmatism with thicker lenses. No statistically significant differences in the distance and near logMAR VA was found between the two lens types using any of the charts used, though, in general, logMAR VA obtained through the thicker lens was better than logMAR VA through the thinner lens. The variabilities in distance and near logMAR VA between the two lens types increased with decreased contrast. The variabilities in distance logMAR VA were greater with Chinese charts than with English charts, and LogMAR VA with Chinese charts were significantly worse for both lens types. Based on the results of this study, we concluded that thicker spherical lathe-cut soft lenses provide better vision in low astigmats. The Snellen acuity test is inadequate for vision assessment of soft contact lens wearers. When a patient wearing thin soft contact lenses complains of poor vision in spite of 6/6 or 6/5 Snellen acuity, changing to thicker lenses may be considered.

Journal Article↗
PubMed2001

Water-soluble antioxidants in human tears: effect of the collection method.

PURPOSE: To resolve differences in published data on tear antioxidant levels by comparing the concentration of water-soluble antioxidants in human reflex tears collected by capillary tube and by the Schirmer strip collection method and in basal and reflex tears collected using the Schirmer strip method. METHODS: Yawn-induced reflex tears (collected simultaneously by capillary tubes and by Schirmer strips) and basal tears (by Schirmer strips and using local anesthetic) were collected from 12 healthy subjects. Tear cysteine, ascorbate, glutathione, urate, and tyrosine were measured by high-performance liquid chromatography within a few minutes of collection. RESULTS: Cysteine, ascorbate, glutathione, and tyrosine were 5 to 10 times higher (P < 0.01) in both reflex and basal tears collected by Schirmer strip compared with reflex tears collected by capillary tube from the same subject. Urate levels were slightly but nonsignificantly higher in Schirmer strip samples (P > 0.05). CONCLUSIONS: The conflict in published data on tear antioxidants is caused by differences in collection methods. With the exception of urate, antioxidants accumulate to very high levels in corneal cells. Spuriously high antioxidant levels in tears collected using Schirmer strips, therefore, are most probably caused by contamination with intracellular constituents. The capillary tube collection method is proposed as the method of choice for reflex tear collection for biochemical studies. This less-invasive method facilitates the evaluation of tear antioxidant levels as a biomonitoring tool for corneal health. Although moderately increased antioxidant levels may be beneficial, the authors hypothesize that marked increases may indicate damage to the ocular surface.

Adult↗
PubMed2000

Tear proteins of normal young Hong Kong Chinese.

BACKGROUND: Analysis of tear proteins is of diagnostic value for abnormal ocular conditions such as dry eye syndrome. Many studies of tear proteins have been performed on Caucasian subjects. However, little is known about these proteins in Chinese eyes. METHODS: The total tear protein concentrations of 30 normal young Hong Kong Chinese were determined by the Bradford method and the modified Lowry method. Bovine serum albumin (BSA) and bovine immunoglobulin G (IgG) were both used as standards for each method. The tear protein patterns were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the concentrations of major tear proteins were quantified by scanning densitometry after SDS-PAGE. RESULTS: The mean +/- SD total tear protein concentrations determined by the Bradford method, using BSA and IgG as standards, were 6.05 +/- 1.58 mg/ml and 11.48 +/- 2.32 mg/ml respectively. The values determined by the modified Lowry method, using the same two standards, were 9.66 +/- 2.03 mg/ml and 7.53 +/- 1.80 mg/ml respectively. The mean +/- SD concentrations of major tear proteins were 2.73 +/- 0.82 mg/ml for lactoferrin, 0.021 +/- 0.028 mg/ml for human serum albumin, 2.89 +/- 0.88 mg/ml for tear-specific prealbumin and 2.46 +/- 0.44 mg/ml for lysozyme. CONCLUSION: The results of total tear protein concentrations indicated that values obtained from different methods and different standards were not comparable. The tear protein patterns of our subjects were qualitatively similar to those reported for Caucasian subjects. However, the concentrations of the major proteins of our subjects were not in accordance with those reported previously. The main reason may be the large variability of method used.

Adolescent↗
PubMed2000

The relationship between total tear protein concentrations determined by different methods and standards.

BACKGROUND: It is known that the values of total protein concentration (TPC) of human tears obtained by different methods/standards vary considerably. The variations are due to differences in reactivity of proteins to the methods used. The aim of this study was to investigate the relationships and agreements between TPC values obtained by different methods/standards. METHODS: Two experiments were conducted. In experiment 1, 30 normal subjects were recruited and their TPC were determined by the Bradford and the modified Lowry methods, with bovine serum albumin and bovine immunoglobulin G as standards. The relationships (equations) between TPC values obtained by different methods/standards were determined. In experiment 2, another 15 normal subjects were recruited and the TPC were measured as in experiment 1. Measured values of TPC using different methods/standards were compared with their respective values calculated from the equations defined in experiment 1. The agreement and the reliability between the measured and the calculated values were investigated. RESULTS: Experiment 1 showed that the TPC obtained by different methods/standards were strongly correlated to one another, and their relationships can be defined by linear equations. In experiment 2, the measured and the calculated values, using the equations defined in experiment 1, showed good agreement and reliability. This indicates that TPC obtained by one method/standard can be used to estimate the value(s) that would be obtained if another method/standard were used using the equation(s) found in experiment 1. CONCLUSION: The correlations between TPC values obtained by different methods/standards were strong. Our results also indicated good agreement and reliability between measured and calculated TPC values. Therefore, values obtained by different methods/standards are interchangeable using the appropriate equations.

Adolescent↗
PubMed2000

Variability of tear protein levels in normal young adults: between-day variation.

BACKGROUND: An adequate knowledge of physiological variation is important for valid comparative studies of tear proteins. The aim of this study was to investigate the between-day variation of the human tear protein levels, including the total protein concentration (TPC) and the levels of major protein fractions. Two sampling methods, the yawn and the eye-flush methods, were used and compared. METHODS: TPC was determined by the Bradford method. The major protein fractions were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and their levels were determined by scanning densitometry after SDS-PAGE. The tear protein levels were monitored for 3 days. RESULTS: The between-day differences in the levels of TPC and the individual protein fractions were not statistically significant in either sampling method, but the variations of some proteins were large and would be clinically significant. Different variations were observed in different proteins. The variations in serum albumin were large, up to 61% and 113% in the yawn and eye-flush methods respectively. The variations in lactoferrin, tear-specific prealbumin and lysozyme were relatively small in the yawn method. The variations in protein levels obtained by the eye-flush method were generally higher than by the yawn method. CONCLUSION: Although the between-day differences in tear protein levels were not statistically significant, the variations in some proteins would be large in magnitude. The variability of tear protein levels obtained by the eye-flush method was larger than that by the yawn method. Therefore, caution should be taken if the eye-flush method is used for sampling tears for quantitative analysis of tear proteins, although it is easier to collect tear samples using this method. The results will be useful to exclude normal variation in tear protein levels when comparing pre- and post-therapeutic tear protein levels in eyes treated for tear-related abnormalities.

Adult↗
PubMed2000

Contact lenses in myopia reduction - from orthofocus to accelerated orthokeratology.

Orthokeratology has been used to provide temporary reduction of myopia since the 1950s and in recent years the development of new lens designs, materials and advanced instrumentation for corneal modelling has resulted in a resurgence in interest in this procedure. In particular, the reverse geometry design has allowed greater myopia reduction. Materials with high oxygen permeability have improved the corneal response to rigid lenses and in orthokeratology they allow overnight retainer lens wear. Corneal modelling systems allow the orthokeratology changes to be monitored and measured, and have increased our understanding of the technique. This paper summarises previous published work in this area and identifies the uncertainties which still remain.

Journal Article↗
PubMed2000

Clinical performances of two disposable soft contact lenses of different materials on Hong Kong-Chinese.

Dryness due to contact lens wear and poor wetting of contact lenses among contact lens wearers is a common observation and contact lens manufacturers have introduced new, better quality soft lens materials that are claimed to be more deposit resistant, and/or dehydration resistant. The purpose of this study was to evaluate and compare the clinical performance of Hydron ActiSoft 60 section sign, made of a new material (HyGMAtrade mark) which is claimed to be dehydration resistant with excellent wettability, with ActiFresh 400, made of conventional non-ionic hydrogel material. The experiment was conducted as a double-masked, randomised, cross-over study. Clinical assessment included pre-lens non-invasive tear break up time (PL-NITBUT), logMar visual acuity and contrast sensitivity (CS). Corneal staining, if any, was recorded at each visit. Subjective ratings in regard to dryness, grittiness, lens awareness, vision, comfort, handling (removal), handling (cleaning) and the overall preference of each lens type were obtained at the end of 3 (Phase A) and 6 months' (Phase B) wear. Twenty-eight subjects successfully completed the study. In Phase A, no significant differences were found in both baseline PL-NITBUT and PL-NITBUT after wearing the same lenses for 1 month between the two lens types. In phase B, baseline PL-NITBUT for ActiFresh 400 was significantly shorter than that for ActiSoft 60. However, after 1 month of wear, the difference in PL-NITBUT between the two lens types was no longer significant. PL-NITBUT was significantly reduced after 1 month's wear for both ActiSoft 60 and Actifresh 400, and in both Phase A and Phase B. The two lens types provided comparable logMAR visual acuity, and there was no significant differences in CS (Pelli Robson) between spectacle lens correction (equivalent spheres) and either lens type. The incidence of corneal epithelial staining was significantly higher and more severe with ActiFresh 400 than with ActiSoft 60, both in Phase A and Phase B. Statistically, there were no significant differences in the scores to the set of questions listed in the questionnaire between the two lens types, except for lens awareness and lens handling. Of the subjects having a preference for one lens, more subjects preferred ActiSoft 60 than ActiFresh 400. In terms of overall preference of the two lens types, at the end of Phase A, 50% of the subjects preferred ActiSoft 60 while only 30% preferred ActiFresh 400, the remaining 20% had no preference. However, by the end of Phase B, preferences for ActiSoft 60 and ActiFresh 400 were comparable. This appeared to be due mainly to the ease of lens handling of the latter.

Journal Article↗
PubMed2000

Endothelial cells analysis with the TOPCON specular microscope SP-2000P and IMAGEnet system.

PURPOSE: Corneal endothelium plays an important role in the maintenance of corneal transparency and stability. The purpose of this study was to evaluate the performance of the TOPCON SP-2000P and IMAGEnet system in terms of (a) the difference in results between automated endothelial cell analysis and retraced cell analysis, (b) the differences in the endothelial cell analysis when using the first image and the clearest of three images taken with the SP-2000P, (c) the repeatability and reproducibility of the IMAGEnet system in the determination of corneal endothelial cell variables, and (d) the repeatability and reproducibility of the SP-2000P in capturing endothelial cell images for endothelial cell analysis. METHODS: Two experiments were performed. Twenty male subjects participated in the first experiment in which endothelial images were captured by examiner SWC and endothelial cell analysis was performed by two examiners, SWC (twice on two different days) and PC (once only). Nineteen male subjects participated in the second experiment in which endothelial cell images were captured by examiners SWC and PC on Visit 1 and by examiner SWC on Visit 2. Endothelial cell analysis was performed by examiner SWC only. The 95% limits of agreements (95%LA) and the intraclass correlation coefficient (ICC) between tested parameters were determined. RESULTS: Automated cell analysis significantly underestimated average cell size (ACS) and hexagonality, and overestimated endothelial cell density (ECD) and coefficient of variance of cell size (CV) (p < 0.05). No statistically significant differences were found in the endothelial cell variables between the first and the clearest images (p > 0.05). There were no statistically significant intra- or inter-examiner differences in any of the endothelial variables determined (p > 0.05). For a set of endothelial cell images, the reproducibility and repeatability of the endothelial cell variables determined with the IMAGEnet system were good, with ICC > 0.9. No significant inter-visit or inter-examiner differences were found (p > 0.05). Reliability was good for the determination of ECD and ACS (ICC > 0.9) but poor or average for the determination of CV and hexagonality (ICC: 0.4-0.8). CONCLUSIONS: We suggest the use of the clearest image with the retraced method for endothelial cell analysis with the IMAGEnet system, as the variability in hexagonality results between the first and the clearest images can be clinically significant. For the same set of images captured by one examiner, the TOPCON IMAGEnet system was reliable in determining ECD and ACS, and was fairly reliable in determining hexagonality and CV. When images were captured on different days or by different examiners, the TOPCON SP-2000P with the IMAGEnet system gives repeatable and reproducible values for ECD and ACS only. Caution should therefore be exercised when using CV and hexagonality to monitor endothelial changes in comparative studies.

Adult↗
PubMed2000

Central and peripheral corneal thickness measured with the TOPCON specular microscope SP-2000P.

PURPOSE: Modern refractive surgery and follow up relies on a knowledge of corneal thickness (CT) and shape, and the reliability of modern instrumentation providing such data is important. This study sought to determine the performance of the TOPCON SP-2000P specular microscope in measuring CT. The aims of this study were: (a) to determine if there is any difference between the CT results obtained from the first image, the clearest of three images and the mean of measurements from three images; (b) to determine the correlation between central and peripheral CT and (c) to investigate the reliability (repeatability and reproducibility) of the SP-2000P in the determination of central and peripheral CT. METHODS: The central and peripheral CT measurements shown on the first (f), the clearest (c) of three images and the mean (m) CT shown in three images captured with the SP-2000P of 43 subjects were compared. All images were captured by the same examiner. Nineteen of the subjects (male) returned on another day and measurements were taken by two examiners. RESULTS: fCT, cCT and mCT were not significantly different from each other. The intraclass correlation coefficients (ICC) between the three values were> 0.9 for all corneal locations measured. However, the variability in the differences between fCT and cCT was relatively greater for peripheral CT (except temporal). The peripheral CT values obtained were all significantly greater than the central CT, and statistically significant correlations were found between the central and each of the peripheral thickness. There was no statistically significant between-visit or between-examiner differences in the central or peripheral CT. The ICC values for between-visit differences for central and temporal measurements were > 0.9 but for the other corneal locations, the ICC values were 0.81 to 0.88. For between-examiner differences, the ICC value was 0.82 for inferior CT and > 0.9 for the other four CT. CONCLUSIONS: Differences in CT measurements obtained from the first and clearest images captured by the SP-2000P were not statistically significant but can be clinically significant for peripheral CT. We therefore suggest the use of the CT value obtained from the clearest of three images. For every unit change in central CT, there is an approximately equivalent change in peripheral CT. Based on the ICC values, the SP-2000P showed very good repeatability and reproducibility in the determination of central CT. For the determination of peripheral CT, the repeatability and reproducibility of the SP-2000P were good and reasonably good respectively. These findings have relevance to the measurement of the cornea before and after refractive surgery.

Adult↗
PubMed2000

Baseline blink rates and the effect of visual task difficulty and position of gaze.

PURPOSE: To compare the baseline blink rates (BBR) measured under different (baseline) conditions, and to compare the blink rates measured when performing two visual tasks of different levels of difficulty at two positions of gaze. METHODS: In the first single masked experiment, BBR were measured under three different conditions - (i) conversation with the subjects (ii) taking the visual acuity and (iii) keeping the subjects waiting in an empty examination room. In the second single masked experiment, the subjects were required to perform an easy task (reading normal English words) and a difficult task (reading mirror-image English words) at primary gaze and down gaze. The orders of the tasks performed were randomly allocated. RESULTS: BBR taken under the three different conditions were significantly different from each other. No significant difference was found between the blink rates measured when performing the two reading tasks if they were performed at the same position of gaze. The mean blink rates were significantly lower when performing the tasks at down gaze than when performing the tasks at primary gaze. No significant differences were found between BBR-waiting and blink rate measured when the subject was doing the easy task at primary gaze, and between BBR-VA and blink rate measured when the subject was performing the difficult task at primary gaze. CONCLUSIONS: BBR measured under different (baseline) conditions produced different results so it is important for investigators to describe the baseline condition very clearly in studies where BBR are measured. Our results also indicated that mean blink rate was affected by the position of gaze and not the level of task difficulty.

Adult↗
PubMed2000

Corneal shape of Hong Kong-Chinese.

Corneal asphericity (the p-value, p) and apical corneal radius (r0) were calculated for 63 Hong Kong-Chinese (39 male and 24 female), using the Topographic Modeling System (TMS-1). The values of p and r0 in, and between, the two principal meridians were compared, and the effects of refractive error and gender were also investigated. The mean +/- SD r0 and p along the flattest meridian of the right eye were 7.82 +/- 0.26 mm and 0.78 +/- 0.12 respectively. The mean +/- SD r0 and p along the steepest meridian of the right eye were 7.64 +/- 0.26 mm and 0.83 +/- 0.15 respectively. Meridional variations were found in r0 and in p. There was no correlation between p and r0 along the two principal meridians. p was not significantly correlated to the refractive error but r0 was. Our results agree with previous findings that while males have longer r0 than females, their p are not significantly different.

China↗
PubMed2000

Ascorbic acid concentration and total antioxidant activity of human tear fluid measured using the FRASC assay.

PURPOSE: To evaluate a novel method (FRASC) for total ferric reducing (antioxidant) activity and ascorbic acid concentration applied to human tears, to investigate the stability of ascorbic acid, and to determine the antioxidant status of human reflex tears. METHODS: Linearity, sensitivity, and precision of FRASC and ascorbic acid loss during 7 days' storage were assessed; total antioxidant activity and ascorbic acid and uric acid concentrations of reflex tears from 47 healthy subjects were measured. RESULTS: FRASC has good precision, linearity, and sensitivity. Ascorbic acid is stable for at least 7 days at moderately acidic pH (pH 3.6) and low temperature. Total antioxidant activity and ascorbic acid and uric acid concentrations (mean +/- SD) in reflex tears were 409 +/- 162, 23 +/- 9.6, and 68 +/- 46 microM, respectively. Ascorbic acid and uric acid constituted around half the total antioxidant activity measured. There was a significant correlation between uric acid and total antioxidant activity (r = 0.754; P: < 0.0001). Men had significantly (P: = 0.0045) higher tear ascorbic acid concentrations than women. CONCLUSIONS: FRASC is suitable for measuring total antioxidant activity and ascorbic acid in human tears. Further clinical study is needed to investigate the male-female difference seen, to characterize the remaining 50% antioxidant activity, and to investigate the effects of environmental conditions, antioxidant supplementation, age, and ocular disease on tear antioxidant status.

Adult↗