Maurice Kh Yap

The University of Hong Kong, Hong Kong, Hong Kong

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Publications (7)12.13 Total impact

  • Sam Ck Cheng · Carly Sy Lam · Maurice Kh Yap ·
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    ABSTRACT: To determine the prevalence and risk factors of myopia-related retinal changes in Hong Kong Chinese adolescents with high myopia. A cross-sectional study on Hong Kong Chinese teenage subjects with high myopia was conducted between January 2005 and June 2009. Subjects were recruited via newspaper advertisements, invitation letters to schools, leaflets and posters. Data collected included history related to myopia progression and retinal characteristics. In total, 120 subjects (61 boys and 59 girls) were recruited. The mean age was 14.8 ± 1.6 years (range: 12-18 years). The mean SER of the eyes was -8.41 ± 1.60 D. Ninety four of the 120 adolescents were found to have a retinal change of which 0.8% were sight-threatening, 2.5% were posterior pole changes, and 61.7% were peripheral retinal changes. The five most frequent retinal changes found were optic nerve crescents (52.5%), white-without-pressure (51.7%), lattice degeneration (5.8%), microcystoid degeneration (5%) and pigmentary degeneration (4.2%). After adjusting for myopia over -8 D, age, gender, duration of myopia, family retinal history and intraocular pressure (IOP), binary logistic regressions showed that an axial length longer than 26.5 mm was a significant risk factor for peripheral retinal changes, optic nerve crescents and white-without-pressure. Peripheral retinal degenerative changes and optic nerve crescent were found in a significant proportion of high myopic teenage subjects. There is increased risk of retinal changes in eyes with an axial length >26.5 mm in 12-18 year-olds.
    Ophthalmic and Physiological Optics 06/2013; 33(6). DOI:10.1111/opo.12082 · 2.18 Impact Factor
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    ABSTRACT: Purpose: Myopia is a complex eye disorder. The X-linked form of complete congenital stationary night blindness (CSNB1A) is usually associated with moderate to high myopia, and is caused by mutations in the NYX gene. We explored if NYX mutations could be associated with high myopia, but not CSNB1A. Methods: The coding regions of the NYX gene were sequenced for 204 Chinese males with high myopia (-8.00 dioptres or worse for both eyes). The frequencies of any sequence variations identified were determined in 200 Chinese males without myopia. Electro-oculography, electroretinography and standard cone function tests were performed on a male high myope carrying a mutation. Results: A missense mutation (c.529_530GC>AT or p.Ala177Met) was identified in one male subject with high myopia, but not in 200 male emmetropes. Neither was this variant found in any of the 529 male and 567 female subjects of various ethnic backgrounds whose genome sequences are documented in the 1000 Genomes Project database. The mutation was predicted to affect the protein function. From ocular electrophysiological tests, the proband was found to have normal rod function, but mildly abnormal cone function and inner retina function. He did not seem to suffer from CSNB1A. Conclusions: One novel missense NYX mutation was identified in an adult male presented with high myopia, but without the major electrophysiological features normally associated with CSNB1A. NYX gene mutations may be considered as one of the rare genetic risk factors for high myopia without key features of CSNB1A.
    Ophthalmic and Physiological Optics 02/2013; 33(3). DOI:10.1111/opo.12036 · 2.18 Impact Factor
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    ABSTRACT: Purpose: To examine the symmetry of corneal changes following near work in the fellow eyes of non-amblyopic myopic anisometropes. Methods: Thirty-four non-amblyopic, myopic anisometropes (minimum 1 D spherical equivalent anisometropia) had corneal topography measured before and after a controlled near work task. Subjects were positioned in a headrest to minimise head movements and read continuous text on a computer monitor for 10 min at an angle of 25 degrees downward gaze and an accommodation demand of 2.5 D. Measures of the morphology of the palpebral aperture during primary and downward gaze were also obtained. Results: The more and less myopic eyes exhibited a high degree of interocular symmetry for measures of palpebral aperture morphology during both primary and downward gaze. Following the near work task, fellow eyes also displayed a symmetrical change in superior corneal topography (hyperopic defocus) which correlated with the position of the upper eyelid during downward gaze. Greater changes in the spherical corneal power vector (M) following reading were associated with a narrower palpebral aperture during downward gaze (p = 0.07 for more myopic and p = 0.03 for less myopic eyes). A significantly greater change in J0 (an increase in against the rule astigmatism) was observed in the more myopic eyes (-0.04 ± 0.04 D) compared to the less myopic eyes (-0.02 ± 0.06 D) over a 6 mm corneal diameter (p = 0.01). Conclusions: Changes in corneal topography following near work are highly symmetrical between the fellow eyes of myopic anisometropes due to the interocular symmetry of the palpebral aperture. However, the more myopic eye exhibits changes in corneal astigmatism of greater magnitude compared to the less myopic eye.
    Ophthalmic and Physiological Optics 01/2013; 33:15-25. DOI:10.1111/opo.12003 · 2.18 Impact Factor
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    ABSTRACT: Background The UMODL1 gene was found to be associated with high myopia in Japanese. This study aimed to investigate this gene for association with high myopia in Chinese. Methods Two groups of unrelated Han Chinese from Hong Kong were recruited using the same criteria: Sample Set 1 comprising 356 controls (spherical equivalent, SE, within ±1 diopter or D) and 356 cases (SE ≤ −8D), and Sample Set 2 comprising 394 controls and 526 cases. Fifty-nine tag single nucleotide polymorphisms (SNPs) were selected and genotyped for Sample Set 1. Four SNPs were followed up with Sample Set 2. Both single-marker and haplotype analyses were performed with cases defined by different SE thresholds. Secondary phenotypes were also analyzed for association with genotypes. Results Data filtering left 57 SNPs for analysis. Single-marker analysis did not reveal any significant differences between cases and controls in the initial study. However, haplotype GCT for markers rs220168-rs220170-rs11911271 showed marginal significance (empirical P = 0.076; SE ≤ −12D for cases), but could not be replicated in the follow-up study. In contrast, non-synonymous SNP rs3819142 was associated with high myopia (SE ≤ −10D) in the follow-up study, but could not be confirmed using Sample Set 1. The SNP rs2839471, positive in the original Japanese study, gave negative results in all our analyses. Exploratory analysis of secondary phenotypes indicated that allele C of rs220120 was associated with anterior chamber depth (adjusted P = 0.0460). Conclusions Common UMODL1 polymorphisms were unlikely to be important in the genetic susceptibility to high myopia in Han Chinese.
    BMC Medical Genetics 08/2012; 13(1):64. DOI:10.1186/1471-2350-13-64 · 2.08 Impact Factor
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    Mavis My Fung · Maurice Kh Yap · Karen Ky Cheng ·
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    ABSTRACT: the prevalence of visual impairment is known to be higher in a diabetic population than in a non-diabetic population. How much of this visual impairment may be attributed to uncorrected refractive error is unclear. This study examined the prevalence of visual impairment in a Hong Kong diabetic population to determine the proportion of the visual impairment that could be corrected with prescription spectacles. patients with type 2 diabetes mellitus (T2DM) were recruited as subjects for this study. All subjects underwent a standardised diabetic retinopathy screening that included measurement of presenting distant vision, biomicroscopic examination of the anterior eye and a retinal examination. For those subjects whose visual acuity was worse than 6/9.5, autorefraction was performed. In this study, we classified visual impairment into three categories: no visual impairment (visual acuity in the better eye better than or equal to 6/18), mild visual impairment (visual acuity in the better eye between 6/18 and 6/60) and severe visual impairment (visual acuity in the better eye less than or equal to 6/60). for the 2,301 subjects who participated in this study, the mean age at examination was 61.4 ± 10.5 years (range, 23 to 92 years). Regarding visual acuity, 11.3 per cent (259/2,301) of subjects had visual impairment with 10.6 per cent being mild (244/2,301) and 0.7 per cent severe (15/2,301). After correction with a prescription determined by autorefraction, the prevalence of visual impairment dropped to 4.0 per cent (91/2,301). Nearly 70 per cent (168/259) of visual impairment was correctable by prescription spectacles and 21.6 per cent (56/259) of subjects were likely to benefit from cataract surgery. for our sample of diabetic patients, nearly 70 per cent of the visual impairment could be remedied by a spectacle correction. In the care of the diabetic eye, eye-care providers should not focus solely on diabetic retinopathy. The quality of life in people with T2DM can be improved simply by eliminating uncorrected refractive errors.
    Clinical and Experimental Optometry 11/2010; 93(6):453-7. DOI:10.1111/j.1444-0938.2010.00539.x · 1.34 Impact Factor
  • Wei Han · William Kwan · Jing Wang · Shea Ping Yip · Maurice Yap ·
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    ABSTRACT: To investigate the influence of eyelid position on wavefront aberrations. In study 1, the right eyes of 43 non-cyclopleged subjects were evaluated using the Complete Ophthalmic Analysis System (COAS) aberrometer. In study 2, the right eyes of the 23 cyclopleged subjects were evaluated using the Optical Pathway Difference Scan aberrometer. Measurements were made with wide-open and deliberately narrowed palpebral apertures in these subjects. In study 3, the influence of eyelashes on the COAS output was investigated in 20 subjects by placing artificial eyelashes in front of the eye, in close proximity to the natural eyelashes. For study 1, the total root mean square (RMS) of the third- and fourth-order aberrations with the wide-open lids was significantly different from the narrowed lid position after the correction for multiple comparisons. There was a difference in the Zernike coefficient of the defocus (C4), 90/180 astigmatism (C5), vertical coma (C7) and spherical aberration terms (C12) between the narrowed and wide-open positions. For study 2, changes were observed with the narrowed lid position in the overall RMS of the third and fourth orders, and total coma aberrations, as well as the specific Zernike coefficients of the C5 and C7 terms. However, none of these changes were significant after the multiple comparison correction. The corneal topography also showed remarkable changes in the superior corneal zone. Placing artificial eyelashes in front of the eye significantly affected some Zernike terms and the RMS of the second and fourth orders, and total coma aberrations, for particular pupil sizes. Deliberate narrowing of the palpebral aperture can influence the wavefront aberrations significantly. The corneal curvature distortion in response to eyelid pressure may account for some of the effect on aberration change. Eyelashes interfering with the light path within the pupil zone distort the output from the COAS, causing significant errors.
    Ophthalmic and Physiological Optics 02/2007; 27(1):66-75. DOI:10.1111/j.1475-1313.2006.00425.x · 2.18 Impact Factor
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Publication Stats

26 Citations
12.13 Total Impact Points


  • 2013
    • The University of Hong Kong
      Hong Kong, Hong Kong
  • 2007-2012
    • The Hong Kong Polytechnic University
      • • School of Optometry
      • • Department of Health Technology and Informatics
      Hong Kong, Hong Kong