Displaying publications 1 - 20 of 30 in total

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  1. Majumder C, Afnan H
    Korean J Ophthalmol, 2020 06;34(3):219-226.
    PMID: 32495530 DOI: 10.3341/kjo.2019.0138
    PURPOSE: The purpose of the study was to establish baseline data for amplitude of accommodation (AA) measured using both subjective and objective techniques in students at a private Malaysian university.

    METHODS: This cross-sectional study was conducted including 34 healthy participants with a mean age of 22.26 ± 1.88 years. AA was measured using dynamic retinoscopy and the push-up, pull-away, modified push-up, and minus-lens techniques.

    RESULTS: The mean AA scores for the push-up, pull-away, minus-lens, and modified push-up techniques and dynamic retinoscopy were 11.38 ± 2.03, 10.35 ± 1.64, 9.24 ± 1.18, 8.26 ± 1.44, and 7.2 ± 1.0 diopters, respectively. No AA measurements showed significant difference among ethnicities (Chinese, Malay, and Indian). This study suggested that AA obtained using push-up (p = 0.005) and pull-away (p = 0.017) methods and dynamic retinoscopy (p = 0.041) were significantly different according to sex. No significant difference was observed in AA for the minus-lens (p = 0.051) and modified push-up (p = 0.216) techniques by sex. A moderately negative correlation was found between AA and age for the push-up (r = -0.434, p = 0.010), pull-away (r = -0.412, p = 0.016), and minus-lens (r = -0.509, p = 0.002) techniques and dynamic retinoscopy (r = -0.497, p = 0.003). A weak negative correlation was found between age and AA measured using a modified push-up technique (r = -0.393, p = 0.022).

    CONCLUSIONS: Mean AA was highest for the push-up technique, followed by the pull-away technique, the minus-lens technique, the modified push up technique, and dynamic retinoscopy. The push-up and pull-away methods and dynamic retinoscopy showed a significant difference in measurement of AA between sexes.

    Matched MeSH terms: Refraction, Ocular/physiology*
  2. Abu Bakar H, Abd Rahim R, Soh PJ, Akkaraekthalin P
    Sensors (Basel), 2021 Jan 26;21(3).
    PMID: 33530534 DOI: 10.3390/s21030827
    Advances in reconfigurable liquid-based reconfigurable antennas are enabling new possibilities to fulfil the requirements of more advanced wireless communication systems. In this review, a comparative analysis of various state-of-the-art concepts and techniques for designing reconfigurable antennas using liquid is presented. First, the electrical properties of different liquids at room temperature commonly used in reconfigurable antennas are identified. This is followed by a discussion of various liquid actuation techniques in enabling high frequency reconfigurability. Next, the liquid-based reconfigurable antennas in literature used to achieve the different types of reconfiguration will be critically reviewed. These include frequency-, polarization-, radiation pattern-, and compound reconfigurability. The current concepts of liquid-based reconfigurable antennas can be classified broadly into three basic approaches: altering the physical (and electrical) dimensions of antennas using liquid; applying liquid-based sections as reactive loads; implementation of liquids as dielectric resonators. Each concept and their design approaches will be examined, outlining their benefits, limitations, and possible future improvements.
    Matched MeSH terms: Refraction, Ocular
  3. Mohd Radzi H, Khairidzan MK, Mohd Zulfaezal CA, Azrin EA
    J Optom, 2019 05 13;12(4):272-277.
    PMID: 31097348 DOI: 10.1016/j.optom.2019.04.001
    PURPOSE: To describe an objective method to accurately quantify corneo-pterygium total area (CPTA) by utilising image analysis method and to evaluate its association with corneal astigmatism (CA).

    METHODS: 120 primary pterygium participants were selected from patients who visited an ophthalmology clinic. We adopted image analysis software in calculating the size of invading pterygium to the cornea. The marking of the calculated area was done manually, and the total area size was measured in pixel. The computed area is defined as the area from the apex of pterygium to the limbal-corneal border. Then, from the pixel, it was transformed into a percentage (%), which represents the CPTA relative to the entire corneal surface area. Intra- and inter-observer reliability testing were performed by repeating the tracing process twice with a different sequence of images at least one (1) month apart. Intraclass correlation (ICC) and scatter plot were used to describe the reliability of measurement.

    RESULTS: The overall mean (N=120) of CPTA was 45.26±13.51% (CI: 42.38-48.36). Reliability for region of interest (ROI) demarcation of CPTA were excellent with intra and inter-agreement of 0.995 (95% CI, 0.994-0.998; P<0.001) and 0.994 (95% CI, 0.992-0.997; P<0.001) respectively. The new method was positively associated with corneal astigmatism (P<0.01). This method was able to predict 37% of the variance in CA compared to 21% using standard method.

    CONCLUSIONS: Image analysis method is useful, reliable and practical in the clinical setting to objectively quantify actual pterygium size, shapes and its effects on the anterior corneal curvature.

    Matched MeSH terms: Refraction, Ocular
  4. Goh PP, Azura R
    Med J Malaysia, 2012 Oct;67(5):497-502.
    PMID: 23770867 MyJurnal
    This is the first population based study on ocular biometric measurements (OBMs) conducted in Malaysia. Its objective is to measure and compare among children of different ethnicity who have myopia and emmetropia. Subsets of children aged between 7 and 8 years old who participated in a larger population based refractive error study had their axial length, anterior chamber depth, lens thickness and vitreous depth measured using A scan and vertical and horizontal corneal curvature measured using an autokeratorefractometer. Eighty eight of the 870 children (10.1%) examined had myopia. Boys, Chinese and children with myopia had significantly longer axial length and vitreous depth compared to girls, Malay and Indian and children who were emmetropic respectively. Girls and children with myopia had steeper corneal curvature. The baseline OBMs in Malaysian children of different ethnicity are valuable for studies in myopia progression. Like other studies, children with myopia have longer axial length (P <0.001). and vitreous depth (P <0.001) compared to children who are emmetropia (without myopia).
    Matched MeSH terms: Refraction, Ocular*
  5. Guan Y, Vossen A, Adachi I, Adamczyk K, Ahn JK, Aihara H, et al.
    Phys Rev Lett, 2019 Feb 01;122(4):042001.
    PMID: 30768311 DOI: 10.1103/PhysRevLett.122.042001
    We report the first observation of the spontaneous polarization of Λ and Λ[over ¯] hyperons transverse to the production plane in e^{+}e^{-} annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive Λ/Λ[over ¯] production, we also report results with subtracted feed-down contributions from Σ^{0} and charm. This measurement uses a dataset of 800.4  fb^{-1} collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the Λ/Λ[over ¯] hyperon.
    Matched MeSH terms: Refraction, Ocular
  6. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Bergauer T, Dragicevic M, et al.
    Phys Rev Lett, 2020 Apr 24;124(16):162002.
    PMID: 32383915 DOI: 10.1103/PhysRevLett.124.162002
    The polarizations of promptly produced χ_{c1} and χ_{c2} mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at sqrt[s]=8  TeV. The χ_{c} states are reconstructed via their radiative decays χ_{c}→J/ψγ, with the photons being measured through conversions to e^{+}e^{-}, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_{c2} to χ_{c1} yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ^{+}μ^{-} decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.
    Matched MeSH terms: Refraction, Ocular
  7. Wu HM, Seet B, Yap EP, Saw SM, Lim TH, Chia KS
    Optom Vis Sci, 2001 Apr;78(4):234-9.
    PMID: 11349931
    PURPOSE: To study interethnic variation in myopia prevalence and severity in young adult males in Singapore and to determine whether these variations are related to differences in education level.

    METHODS: A population-based survey of refractive errors in a cohort of 15,095 military conscripts between July 1996 and June 1997 using noncycloplegic autorefraction and a standard questionnaire. Prevalence rates of myopia (

    Matched MeSH terms: Refraction, Ocular
  8. Chung KM
    Optom Vis Sci, 1999 Feb;76(2):121-6.
    PMID: 10082059
    The clinical significance of fundus magnification produced during direct ophthalmoscopy of the corrected eye has not been fully established. Based on paraxial ray tracing, fundus magnification (M) can be defined by a simple equation, M = (K'/4) x (Fs/K), where K' is the dioptric axial power of the eye, Fs is the correcting thin lens power and K is the ocular ametropia. Refractive myopes produce greater fundus magnification than axial myopes, whereas refractive hyperopes produce lower fundus magnification than axial hyperopes. If we assume 15 x fundus magnification as our standard magnification for an emmetropic reduced eye, then wearing glasses or putting the focusing lens at or close to the anterior focus of the eye is able to achieve the standard magnification for axial myope and axial hyperope, whereas wearing contact lenses is able to achieve the standard magnification for refractive myope and refractive hyperope. Vertex distance has greater influence on fundus magnification produced during direct ophthalmoscopy than other funduscopic techniques. In conclusion, the newly defined formula has clinical applications during direct ophthalmoscopy.
    Matched MeSH terms: Refraction, Ocular
  9. Chung KM
    Optom Vis Sci, 1993 Mar;70(3):228-33.
    PMID: 8483585
    Studies of optical defocus on refractive development and ocular growth in animals are presented and discussed in relation to the accommodation hypothesis. None of these studies fully support the accommodation hypothesis. The problems encountered in these studies are also discussed.
    Matched MeSH terms: Refraction, Ocular
  10. Goh PP, Abqariyah Y, Pokharel GP, Ellwein LB
    Ophthalmology, 2005 Apr;112(4):678-85.
    PMID: 15808262 DOI: 10.1016/j.ophtha.2004.10.048
    To assess the prevalence of refractive error and visual impairment in school-age children in Gombak District, a suburban area near Kuala Lumpur city.
    Matched MeSH terms: Refraction, Ocular
  11. Jasman AA, Shaharuddin B, Noor RA, Ismail S, Ghani ZA, Embong Z
    BMC Ophthalmol, 2010;10:20.
    PMID: 20738840 DOI: 10.1186/1471-2415-10-20
    Despite growing number of intraocular lens power calculation formulas, there is no evidence that these formulas have good predictive accuracy in pediatric, whose eyes are still undergoing rapid growth and refractive changes. This study is intended to compare the prediction error and the accuracy of predictability of intraocular lens power calculation in pediatric patients at 3 month post cataract surgery with primary implantation of an intraocular lens using SRK II versus Pediatric IOL Calculator for pediatric intraocular lens calculation. Pediatric IOL Calculator is a modification of SRK II using Holladay algorithm. This program attempts to predict the refraction of a pseudophakic child as he grows, using a Holladay algorithm model. This model is based on refraction measurements of pediatric aphakic eyes. Pediatric IOL Calculator uses computer software for intraocular lens calculation.
    Matched MeSH terms: Refraction, Ocular/physiology*
  12. Lim KL, Fam HB
    J Refract Surg, 2006 Apr;22(4):406-8.
    PMID: 16629076
    PURPOSE: To evaluate a novel non-surgical method for improving vision in a refractive surgery patient.

    METHODS: A 45-year-old man who had undergone LASIK 5 years previously presented with blurred distance vision. Unaided vision in the right eye was 20/329-2) and 20/20 in the left eye. He enrolled for NeuroVision treatment (NeuroVision Pte Ltd, Singapore), a computer-based interface in which a repetitive set of visual excerises is performed for 10 to 12 weeks.

    RESULTS: After 35 sessions, unaided visual acuity in the right eye was 20/16(-3) and 20/20(-1) in the left eye, representing 2.8 lines of improvement in the right eye and 1.6 lines in the left eye.

    CONCLUSIONS: NeuroVision, a noninvasive treatment based on the concept of perceptual learning, is a benefit in cases in which surgical enhancement is not recommended.

    Matched MeSH terms: Refraction, Ocular/physiology*
  13. Choong YF, Chen AH, Goh PP
    Am J Ophthalmol, 2006 Jul;142(1):68-74.
    PMID: 16815252 DOI: 10.1016/j.ajo.2006.01.084
    To evaluate the accuracy of autorefraction using three autorefractors comparing to subjective refraction in diagnosing refractive error in children.
    Matched MeSH terms: Refraction, Ocular*
  14. Chen RP, Chen Z, Chew KH, Li PG, Yu Z, Ding J, et al.
    Sci Rep, 2015;5:10628.
    PMID: 26024434 DOI: 10.1038/srep10628
    A caustic vector vortex optical field is experimentally generated and demonstrated by a caustic-based approach. The desired caustic with arbitrary acceleration trajectories, as well as the structured states of polarization (SoP) and vortex orders located in different positions in the field cross-section, is generated by imposing the corresponding spatial phase function in a vector vortex optical field. Our study reveals that different spin and orbital angular momentum flux distributions (including opposite directions) in different positions in the cross-section of a caustic vector vortex optical field can be dynamically managed during propagation by intentionally choosing the initial polarization and vortex topological charges, as a result of the modulation of the caustic phase. We find that the SoP in the field cross-section rotates during propagation due to the existence of the vortex. The unique structured feature of the caustic vector vortex optical field opens the possibility of multi-manipulation of optical angular momentum fluxes and SoP, leading to more complex manipulation of the optical field scenarios. Thus this approach further expands the functionality of an optical system.
    Matched MeSH terms: Refraction, Ocular
  15. Hashim SE, Tan HK, Wan-Hazabbah WH, Ibrahim M
    Ann Acad Med Singap, 2008 Nov;37(11):940-6.
    PMID: 19082201
    INTRODUCTION: Refractive error remains one of the primary causes of visual impairment in children worldwide, and the prevalence of refractive error varies widely. The objective of this study was to determine the prevalence of refractive error and study the possible associated factors inducing refractive error among primary school children of Malay ethnicity in the suburban area of Kota Bharu, Kelantan, Malaysia.

    MATERIALS AND METHODS: A school-based cross-sectional study was performed from January to July 2006 by random selection on Standard 1 to Standard 6 students of 10 primary schools in the Kota Bharu district. Visual acuity assessment was measured using logMAR ETDRS chart. Positive predictive value of uncorrected visual acuity equal or worse than 20/40, was used as a cut-off point for further evaluation by automated refraction and retinoscopic refraction.

    RESULTS: A total of 840 students were enumerated but only 705 were examined. The prevalence of uncorrected visual impairment was seen in 54 (7.7%) children. The main cause of the uncorrected visual impairment was refractive error which contributed to 90.7% of the total, and with 7.0% prevalence for the studied population. Myopia is the most common type of refractive error among children aged 6 to 12 years with prevalence of 5.4%, followed by hyperopia at 1.0% and astigmatism at 0.6%. A significant positive correlation was noted between myopia development with increasing age (P <0.005), more hours spent on reading books (P <0.005) and background history of siblings with glasses (P <0.005) and whose parents are of higher educational level (P <0.005). Malays in suburban Kelantan (5.4%) have the lowest prevalence of myopia compared with Malays in the metropolitan cities of Kuala Lumpur (9.2%) and Singapore (22.1%).

    CONCLUSION: The ethnicity-specific prevalence rate of myopia was the lowest among Malays in Kota Bharu, followed by Kuala Lumpur, and is the highest among Singaporean Malays. Better socio-economic factors could have contributed to higher myopia rates in the cities, since the genetic background of these ethnic Malays are similar.

    Matched MeSH terms: Refraction, Ocular
  16. Wu AL, Ling KP, Chuang LH, Chen KJ, Chen YP, Yeung L, et al.
    Acta Ophthalmol, 2020 Nov;98(7):e839-e847.
    PMID: 32243725 DOI: 10.1111/aos.14418
    PURPOSE: To investigate the long-term surgical outcomes of macular hole retinal detachment (MHRD) following vitrectomy with macular plug in highly myopic eyes.

    METHODS: Thirty-five cases of highly myopic eyes with MHRD in 35 patients who underwent an initially successful vitrectomy with macular plug and were followed up for at least 3 years were reviewed. The anatomical outcomes were evaluated by fundus examination, fundus photographs and optical coherence tomography (OCT). Myopic features after the surgery were differentiated according to recommendations of the Meta-analysis of Pathologic Myopia (META-PM) Study Group. The best-corrected visual acuities (BCVAs) before and after surgery were analysed as the functional outcome. Main outcome measures time-course changes in BCVA and complications.

    RESULTS: The mean patient age was 61.0 ± 11.4 years. The follow-up was 45.2 ± 8.6 months (ranged from 36 to 71 months). The mean axial length was 29.3 ± 1.2 mm. All eyes demonstrated attached retina, but 2 eyes (5.7%) developed reopened macular holes until the last follow-up. Complications of postoperative rhegmatogenous retinal detachment were detected in 2 eyes (5.7%) within 1 year and retina reattached after the secondary vitrectomy. Three cases (8.6%) of prolonged subretinal fluid lasting more than 1 year were detected but finally absorbed completely. Comparing 1-3 years postoperatively, myopic features showed significant progression of myopic maculopathy category (p = 0.035). Functionally, significantly improved BCVA could be maintained postoperatively between 6 months and 3 years. However, vision of 14 eyes (40.0%) worsened within 1-3 years postoperatively, and visual deterioration was associated with progression of myopic maculopathy (p = 0.004) and pre-existing disease of glaucoma (p = 0.006).

    CONCLUSIONS: A vitrectomy combined with macular plug provided favourable outcomes in the long term, over the ≥3-year follow-up period.

    Matched MeSH terms: Refraction, Ocular/physiology*
  17. Fam HB, Lim KL
    J Cataract Refract Surg, 2006 Aug;32(8):1281-7.
    PMID: 16863962 DOI: 10.1016/j.jcrs.2006.02.060
    PURPOSE: To determine an index that distinguishes keratoconus and keratoconus-suspect eyes from normal eyes with Orbscan (Bausch & Lomb) corneal elevation maps.
    SETTING: Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, and iLaser Centre, Island Hospital, Penang, Malaysia.
    METHODS: In this initial phase of this multicenter nonrandomized retrospective study, 1 eye of 166 normal subjects, 15 keratoconus patients, and 11 keratoconus suspects was examined at 1 clinic. The anterior best-fit sphere (BFS), posterior BFS, anterior elevation, posterior elevation, and maximum and minimum keratometries were analyzed. Two indices with the highest sensitivity and specificity classifying these conditions were identified using receiver operating characteristic curves. These 2 indices were evaluated in a subsequent validation study using 1 eye of 221 normal subjects, 43 keratoconus patients, and 23 keratoconus suspects from another clinic.
    RESULTS: The anterior elevation and anterior elevation ratio (anterior elevation ratio = anterior elevation/anterior BFS) best classified the different groups. An anterior elevation ratio of 0.5122 mm or less had 99% sensitivity and 95.2% specificity while a ratio 16.5 mum or less had 80.1% sensitivity and 80.8% specificity in discriminating normal eyes from keratoconus and keratoconus suspects. The results were similar in the validation study. In addition, these anterior elevation and anterior elevation ratio cutoff values had high sensitivity and specificity in identifying keratoconus suspects from normal eyes in the validation study.
    CONCLUSION: Anterior corneal elevation parameters are clinically relevant measures for detecting keratoconus and suspected keratoconus eyes.
    Matched MeSH terms: Refraction, Ocular
  18. Au Eong KG, Tay TH, Lim MK
    Singapore Med J, 1993 Dec;34(6):489-92.
    PMID: 8153707
    Computerised data of 110,236 Singaporean males aged 15 to 25 (mean 17.75) years who underwent compulsory medical examination from April 1987 to January 1992 were used to estimate the prevalence and severity of myopia among young Chinese, Malay, Indian and Eurasian Singaporean males with different educational levels. The prevalence and severity of myopia amongst the groups with different educational levels were compared. These groups were fairly well-matched for important known confounding factors such as age, sex, race and degree of urbanisation of place of residence. Our data showed a positive association between educational attainment and both the prevalence and severity of myopia. Both the prevalence of myopia and the proportion of myopes with severe myopia were in general higher among those with more years of formal education.
    Matched MeSH terms: Refraction, Ocular
  19. Kuan BB, Lim TK
    Med J Malaysia, 1984 Dec;39(4):280-4.
    PMID: 6544933
    Ultrasound measurement of ocular dimension is the chosen method for assessing axial length when determining dioptric power for intraocular lens. From the current results of 30 cases studied, the mean axial length ranges from 22 to 23 mm. Despite the limitation of the accuracy of the ultrasonic measurements with the 7.5 mHz transducer, the power of intraocular lens can. be determined satisfactorily in accordance with the knowledge of keratometric reading. Hence, high refractive errors could be avoided post-operatively.
    Matched MeSH terms: Refraction, Ocular
  20. Radhakrishnan H, Hartwig A, Charman WN, Llorente L
    Clin Exp Optom, 2015 Nov;98(6):527-34.
    PMID: 26450168 DOI: 10.1111/cxo.12296
    BACKGROUND: Differences in accommodation when reading Chinese, as compared to Latin, characters have been suggested to have a role in the higher prevalence of myopia in some Asian countries. Yeo and colleagues (Optom Vis Sci 2013; 90: 156-163) found that, in Chinese-literate children, accommodation was marginally more accurate (by less than 0.05 D), when reading Chinese text. This was attributed to the additional cognitive demand associated with interpreting the more complex Chinese symbols. The present study compared responses to single Chinese and Latin characters, while controlling for cognitive demand.
    METHODS: The monocular accommodative response was measured in Chinese-illiterate adults (10 emmetropes, mean spherical equivalent: -0.07 ± 0.42 D, age: 29.9 ± 4.2 years; 11 myopes, mean spherical equivalent: -4.28 ± 2.84 D, age: 31.7 ± 4.6 years) with an open-field autorefractor. Four Chinese and three Latin characters (approximately 1.15 degrees subtense) were individually presented on a display screen one metre away from the subject, while their vergence was varied over the range zero to 5.00 D using spectacle trial lenses. The slope and the accommodative error index (AEI) were calculated from the accommodative stimulus/response curves (ASRC).
    RESULTS: No statistically significant differences were found between refractive groups or among characters within the same refractive group in ARSC slopes (Latin: 0.87 ± 0.14 for myopes versus 0.81 ± 0.12 for emmetropes; Chinese: 0.84 ± 0.12 for myopes versus 0.85 ± 0.12 for emmetropes). No significant differences were found between characters in accommodative error index either (Latin, 0.78 ± 0.42 D for myopes versus 1.15 ± 0.72 D for emmetropes; Chinese, 0.74 ± 0.37 D for myopes versus 1.17 ± 0.83 D for emmetropes). However, accommodative error indices and accommodative errors were significantly higher for emmetropes.
    CONCLUSION: Under controlled cognitive demand, Chinese and Latin characters elicited similar responses in both individual refractive groups. This study fails to support the hypothesis that development of myopia in some Asian populations is associated with larger lags of accommodation when reading or viewing Chinese characters.
    Study site: Manchester, United Kingdom
    Matched MeSH terms: Refraction, Ocular/physiology*
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