bluuebunny/crossref_metadata_2025_split huggingface dataset:
Colour vision screening among Saudi Arabian children
Authors: Oriowo O. Matthew , Alotaibi Abdullah Z. 
Published: October 2016

Purpose: To determine the prevalence of congenital red-green colour vision defects among Saudi Arabian male and female children.Methods: The study involved 1638 elementary and high school participants (838 males, and 800 females), who were randomly selected and screened for red-green colour vision defects using the Ishihara (pseudo-isochromatic plates) test. Inclusion criteria were Snellen VA 20/20 or better and absence of known ocular pathologies.Among the females, 0.75% of the 800 participants showed CVD, with 0.25% and 0.5% demonstratingprotan and deutan defects, respectively.Conclusion: The results show that the prevalence of red-green colour deficiency among the female children from central Saudi Arabia is not significantly different from that of female populations inwestern countries. The current prevalence among the males is higher than previously reported for central Saudi Arabia, but less than for Caucasian populations.
An assessment of the level of diabetic patients’ knowledge of diabetes mellitus, its complications and management in Durban, South Africa
Authors: Mashige K. P. , Notshweleka A. , Moodley S. , Rahmtoola F. H. , Sayed S. B. , Singh S. , Sardiwalla Z. 
Published: October 2016

Epidemiological data shows that Diabetes Mellitus (DM) in South Africa is increasing with changes in lifestyles and ageing of the population. Early diagnosis and management of DM is an important factor for limiting visual and physical complications of the disease. The purpose of this study was to establish the level of knowledge about DM, its ocular complications and management protocol amongst diabetic patients. A questionnaire was provided to a total of 106 diabetic patients attending the Tongaat Community Clinic, the University of KwaZulu Natal Eye Clinic and the Diabetic Awareness day in Chatsworth. All patients were receiving treatment for DM. The questionnaire consisted of questions relating to the patients’ knowledge of the disease, its ocular complications and its management. The respondents were mostly females (65%), aged between 30 to 85 years (mean = 52.45 ± 3.75 years). The majority (96%) of respondents knew about the existence of two main types of DM and 77% reported having Type 2 DM, 18% reported having Type 1 DM, and only 5% did not know the type of DM that they had. Many respondents thought that hereditary factors (78%), and diet and lifestyle modifications (77%), were important risk factors in the development of DM. Glucose levelcontrol (84%) and duration (85%) were thought as important risk factors for its complications. Although many subjects (66.1%) were aware of the visual threat that DM posed, only 42%, 44% and 53% knew that DM could result in diabetic retinopathy, cataracts and glaucoma respectively. Less than half (48.3%) of the respondents had their last eye examination more than a year and a half ago. A significant proportion (60.8%) reported that the threat to vision was reason enough for them to have regular eye examinations. A large proportion (76%) of respondents reported that they had adequate knowledge of management of DM. Many (81%) of the respondents reported routinely controlling their DM through diet, 65% through exercise, 84% through sugar monitoring and 76% through regular medical examinations. The participants in this study had a significant knowledge of DM and its management. However, their knowledge of ocular effects was limited. These results highlight the need for educational programmes aimed at improving the knowledge of the effects of DM on the eyes including the need for regular eye examinations.
A review of the use of Streptozotocin (STZ) in the induction of diabetes in rats and subsequent ocular tissue changes
Authors: Sithole H. L. 
Published: October 2016

Streptozotocin is widely used in medical research for treating certain cancers of the Islets of Langerhans and to produce an animal model for type 1 diabetes. A study has revealed that when compared to the control group of rats, those injected with STZ exhibited reduced plasma insulin and elevated blood glucose (p < 0.05 in all cases). The study also found that diabetic rats weighed significantly less than control animals (p < 0.05). In relation to ocular tissues, lacrimal glands from diabetic rats were also found to weigh significantly less (p < 0.05) than those from the control group. However, no significant changes in the weights of lens, cornea, sclera and retina were observed between diabeticand control animals. Several other studies found that STZ-induced diabetes can be treated by plant extracts which control the blood sugar level as well as improving the lipid profile and ocular complications such as retinopathy. Experiments are usuallyperformed on male or female rats of a specific body weight, usually between 250 and 300 g. Diabetes is induced in rats by intraperitonial injections of streptozotocin (60 mg/ kg) in citrate buffer, pH 6.3.Animals that exhibit glucosuria after 24 hours, test-ed by urine test strips are considered diabetic. Plant extracts (6 mg/100g body weight) are orally administered into the stomach of STZ-diabetic rats every third day at a certain consistent time by means of bulbed steel needle for at least a four week period. This is done to determine the efficacy and potency of the plant extracts on diabetes. Histological and transmission electron microscope (TEM) techniques are used to study the changes in the ocular tissues. The dissected ocular tissues should be dehydrated in graded ethyl alcohol series and embedded in Araldite CY212. Ultra thin sections should be contrasted with uranyl acetate and lead citrate for examination by TEM. Streptozotocin induces diabetes in laboratory animal models for scientific studies and breakthroughs in medicine. The use of STZ and plant extracts may prove to be beneficial in the eye health care profession if considered for the studies of hypoglycemic agents that have the potency to prevent the advancement of diabetic retinopathy in diabetic patients.
Ray pencils of general divergency
Authors: Harris W. F. 
Published: October 2016

That a thin refracting element can have a dioptric power which is asymmetric immediately raises questions at the fundamentals of linear optics. In optometry the important concept of vergence, in particular, depends on the concept of a pencil of rays which in turn depends on the existence of a focus. But systems that contain refracting elements of asymmetric power may have no focus at all. Thus the existence of thin systems with asym-metric power forces one to go back to basics and redevelop a linear optics from scratch that is sufficiently general to be able to accommodate suchsystems. This paper offers an axiomatic approach to such a generalized linear optics. The paper makes use of two axioms: (i) a ray in a homogeneous medium is a segment of a straight line, and (ii) at an interface between two homogeneous media a ray refracts according to Snell’s equation. The familiar paraxial assumption of linear optics is also made. From the axioms a pencil of rays at a transverse plane T in a homogeneous medium is defined formally (Definition 1) as an equivalence relation with no necessary association with a focus. At T the reduced inclination of a ray in a pencil is an af-fine function of its transverse position. If the pencilis centred the function is linear. The multiplying factor M, called the divergency of the pencil at T, is a real 2 2× matrix. Equations are derived for the change of divergency across thin systems and homogeneous gaps. Although divergency is un-defined at refracting surfaces and focal planes the pencil of rays is defined at every transverse plane ina system (Definition 2). The eigenstructure gives aprincipal meridional representation of divergency;and divergency can be decomposed into four natural components. Depending on its divergency a pencil in a homogeneous gap may have exactly one point focus, one line focus, two line foci or no foci.Equations are presented for the position of a focusand of its orientation in the case of a line focus. All possible cases are examined. The equations allow matrix step-along procedures for optical systems in general including those with elements that haveasymmetric power. The negative of the divergencyis the (generalized) vergence of the pencil.
Short-term variation in ocular anterior chamber angle using Scheimpflug photography
Authors: Rubin A. 
Published: October 2016

Purpose: To investigate short-term variation of ocular Anterior Chamber Angle (ACA) within and across the different meridians of young, healthy eyes.Method: Scheimpflug photography (via an Oculus Pentacam) was used to repeatedly measure the anterior segment of the right eyes of three young females, all aged 22 years. For each individual, ten consecutive maps were determined over a short time period and each map contained information for the chamber angles of different meridians across the eye involved, roughly at 70 intervals. Each meridian in an eye was thus measured 10 times in total permitting analysis of short-term variation both within and across the meridians concerned. Parametric and non-parametric statistical methods used to understand short-term variation of ACA included meridional plots of medians andlower and upper quartiles (Q1 and Q3) and various polar plots (of raw observations, of means and 95%confidence regions, and of standard deviations).Results: Over, at least, short periods of time, Scheimpflug photography provided fairly repeatable results for ACA both within and across the meridians of the eyes involved. However, occasionally outliers increased variability for some meridians. While short-term variation within meridians was relatively small assuming exclusion of a limitednumber of outliers, variation across the meridians of specific eyes was greater (probably relating to the usual anatomical structure of eyes with ACA in the inferior quadrants being mostly larger than that for the superior quadrants). Friedman ANOVA confirmed for each of the three eyes concerned thamedian ACA was significantly different across thvarious meridians.Conclusion: Scheimpflug photography allows for comprehensive, non-invasive and rapid measurement of ACA through 3600. Repeatability of measurements appears satisfactory over the short-term, despite potential limitations relating to this photo-graphic method for measuring ACA. The holistic and quantitative approach to ACA used here may be useful also in diabetic, neoplastic or other disease of the anterior segment of the eye. This methodology could provide better understanding of the potential risk for acute or chronic angle-closure glaucoma through more complete evaluation of ACA. The methods also could be usefully applied to measurement of ACA using techniques such as anterior segment optical coherence tomography or ultrasound biomicroscopy. (S Afr Optom 2010 69(1) 35-47)
Optical lenses and magnification in archery*
Authors: Strydom B. , Ferreira J. T. 
Published: October 2016

The use of optical lenses to increase or magnify a target of concern is commonly used in compound bow archery. The principles and factors that may influence the use of these lenses may, however, not be fully understood by archers. Two types of lens systems, the one-lens system and the two-lens system, as described by the authors, may be used. Different factors such as the draw length of the archer,the ametropic condition of the archer, depth of field, depth of focus, age, accommodation, the power of F1 and F2 (see Figures 1 and 2 in the paper) and the distance the lens is placed from the archer may influence the results of the lens used by the archer. (S Afr Optom 2010 69(1) 29-34)
Optical axes of catadioptric systems including visual, Purkinje and other nonvisual systems of a heterocentric astigmatic eye
Authors: Harris W. F. 
Published: October 2016

For a dioptric system with elements which may be heterocentric and astigmatic an optical axis has been defined to be a straight line along which a ray both enters and emerges from the system. Previous work shows that the dioptric system may or may not have an optical axis and that, if it does have one, then that optical axis may or may not be unique. Formulae were derived for the locations of any optical axes. The purpose of this paper is to extend those results to allow for reflecting surfaces in the system in addition to refracting elements. Thus the paper locates any optical axes in catadioptric systems (including dioptric systems as a special case). The reflecting surfaces may be astigmatic and decentred or tilted. The theory is illustrated by means of numerical examples. The locations of the optical axes are calculated for seven optical systems associated with a particular heterocentric astigmatic model eye. The optical systems are the visual system, the four Purkinje systems and two other nonvisual systems of the eye. The Purkinje systems each have an infinity of optical axes whereas the other nonvisual systems, and the visual system, each have a unique optical axis. (S Afr Optom 2010 69(3) 152-160)
Generalized magnification in visual optics. Part 1: Magnification as linear transformation
Authors: Harris W. F. 
Published: October 2016

In Gaussian optics magnification is a scalar; the interpretation is obvious. In linear optics, the simplest optics of astigmatic systems, the generalization is a 2 2× real matrix and, in general, is much harder to interpret. This generalized magnification may imply magnification in the familiar sense that differs from one meridian to another, shear distortion, rotation, reflection, inversion, magnification in the familiar sense or combinations of these effects. The purpose of this paper is to illustrate generalized magnification and to provide a comprehensive interpretation. Because the treatment is abstract it can be applied to blur and size magnification and to any magnification that can be represented by a 2 X 2 matrix. (S Afr Optom 2010 69(3) 109-122)
Eye health promotion in the South African primary health care system*
Authors: Sithole H. L. , Oduntan O. A. 
Published: October 2016

Objective: There is currently very little or no research being done in South Africa on eye health promotion. Also, there is no evidence of any existing eye health promotion policy in the South African primary health care system. The purpose of this paper therefore is to highlight the lack of an integrated eye health promotion policy in the South African primary health care system.Approach: A literature review of research databases was conducted to identify research done in the previous years pertinent to eye health promotion in South Africa. Also, documents were requested from the South African National Department of Health to ascertain claims of any existing guidelines on eye care. It was found that these documents included the national guidelines on prevention of blindness, refractive error screening for persons 60 years and older, cataract surgery in South Africa, management and control of eye conditions at primary level.Although there is currently no integrated eye health promotion policy in South Africa, the fragmented national guidelines represent the existing policies on eye health promotion. The custodians of these policies are the eye care coordinators located in each of the nine provinces.Conclusion: Although there are eye care coordinators in each province, there is no evidence of any eye health promotion activities being done in those provinces. Also, only one province out of nine has dedicated health promotion personnel that are not only focusing on eye health matters. This greatly compromises the initiatives of eliminating avoidable blindness. It is therefore recommended that an integrated eye health promotion model be developed so that it may form part of the South African primary health care system. (S Afr Optom 201069(4) 200-206)
Graphical construction of cardinal points from the transference
Authors: Harris W. F. 
Published: October 2016

Usually nodal, principal and focal points are defined independently and thought of as distinct structures with no simple relationship among them. By adopting a holistic approach, in which these threetypes of cardinal points are treated as particular cases of a larger class of special points, this paper develops a method of constructing the locations of the cardinal points of a system graphically directly from the transference. The method provides a useful way of visualising the relationship of the locations of the cardinal points and of how they are affected by changes in the system or when a second optical system is placed in front of the first. Thepaper illustrates the graphical procedure by apply-ing it in several situations of interest in optometryand ophthalmology, including the effect of a contact lens or refractive surgery on a reduced eye and the effect of accommodation, a spectacle lens and an afocal telescope on the Gullstrand-Emsleyschematic eye. (S Afr Optom 2011 70(1) 3-13)
A comparison of the visual status of dyslexic and non-dyslexic schoolchildren in Durban, South Africa
Authors: Wajuihian S. O. , Naidoo K. S. 
Published: October 2016

Background: Reading difficulties constitute an impediment to the learning process and in the educational achievement of a child. Consequently, several studies examined the visual status of dyslexic children in the Caucasian populations. Such studies are lacking in the African populations.Aim: To determine the prevalence of vision defects and investigate if there is an association between dyslexia and vision in a South African population of dyslexic school children. Methods: This comparative study assessed the visual function of 62 children (31 dyslexic and 31 normally-reading children), mean age 13 ± 1.42 years and 11.90 ± 0.93 years respectively. The participants were matched for gender, race and socio-economic status. The visual functions evaluated and the techniques used were: visual acuity (LogMAR acuity chart), refraction (static retinos-copy), ocular alignment (cover test) near point of convergence (RAF rule), accommodation facility (± 2 D flipper lenses), amplitude of accommodation (push-up method) relative accommodation(trial lenses) accommodation posture (monocular estimation technique) and vergence reserves (prism bars). Results: In the following, results are provided for the dyslexic versus control: Refractive errors: (hyperopia 6.5% vs 3%,) (myopia 6.5% vs 6.5%), (astigmatism 10% vs 13%), (anisometropia 6.5% vs 6.5%) (amblyopia 6.5% vs 0%), (remote NPC 33% vs 48%) (esophoria at near 3% vs 0%) (exophoria at near 9.5% vs 0%), (accommodative infacility at near 54% vs 33%), lag of accommodation 39.28% vs 41,93%, (poor positive fusional amplitude at near, 25% vs 16%). Only the binocular accommodative facility at near was significantly associated with dyslexia (p=0.027). Conclusion: The prevalence of vision defects was similar between the dyslexic and non-dyslexic participants, which suggest that an association between dyslexia and vision variables investigated, cannot be inferred. This study provides a research perspective on the prevalence of vision defects in a Black South African population of dyslexic children and has clinical relevance and implications for the assessment, detection and management of vision anomalies in dyslexic schoolchildren. (S Afr Optom 2011 70(1) 29-43)
Intraocular pressure in postmenopausal Nigerian women with and without systemic hypertension
Authors: Ebeigbe J. A. , Ebeigbe P. N. , Ighoroje A. D. A 
Published: October 2016

Background: Mean intraocular pressure (IOP) in postmenopausal women has been reported higher than that in menstruating women. Also, intraocular pressure is said to be positively correlated with systemic blood pressure. No previous study in Nigeria has compared intraocular pressure in postmenopausal women with and without systemic hypertension. Purpose: To investigate the effects of menopause on intraocular pressure in subjects with and without high blood pressure. Methods: Normotensive and hypertensive premenopausal and postmenopausal subjects in the same agerange of 45 to 55 years were studied. Intraocular pressure was measured with the hand-held Kowa applanation tonometer. Blood pressure was taken in the sitting position at the right upper arm using a manual mercury sphygmomanometer with the right cuff size. The average of two readings was recorded. Results: Mean IOP for premenopausal normotensive women was 14.58 ± 2.56 mmHg whilethat of postmenopausal normotensive women was16.15 ± 1.80 mmHg (p<0.05). Also, the difference in mean IOP between premenopausal hypertensive (16.58 ± 3.23 mmHg) and postmenopausal hypertensive women (18.24 ± 3.89 mmHg)was statistically significant (p<0.05). A statistically significant and positive correlation was observed between IOP and systemic blood pressure in postmenopausal hypertensive women, p<0.05.Conclusion: Menopause significantly increases intraocular pressure. Mean intraocular pressure of hypertensive postmenopausal women was significantly higher than that of normotensive post-menopausal women, (p<0.05). Knowledge of the normal level of intraocular pressure during various stages of the female reproductive cycle may help during glaucoma screening. (S Afr Optom 2011 70(3) 117-122)
Short-term variation in central corneal thick- ness and intraocular pressure using the Tono-Pachymeter NT530P (Tonopachy™)
Authors: Mashige R. M. , Rampersad N. 
Published: October 2016

Measurements of central corneal thickness (CCT) and intra-ocular pressure (IOP) are important for both diagnostic and therapeutic purposes. The aim of this study was to investigate the short-term variation and intra-subject repeatability of CCT and IOP measurements made with the Tono-Pachymeter NT530P (Tonopachy™). Fifty one consecutive automatic measurements of CCT and IOP were taken for the right eyes of 15 subjects (11 females and 4 males) aged 20 to 57 years (mean = 32.3 ± 13.5 years). The measured values (CCT and IOP) were compared against each other to establish the intra-subject repeatability and bias of each individual measurement with respect to the means, standard deviations and variances. Three different statistical tests of normality: Kolmogorov-Smirnov (K-S),Lilliefors and Shapiro-Wilks (SW) tests suggested that most of the data was normally distributed,with a few exceptions. The inter-subject or overall mean values and standard deviations for the CCT and IOP samples were 528.2 ± 27.4 μm and 14.4 ±4.3 mmHg respectively. Although possible outliers increased the variability of the measurements of both parameters (CCT and IOP), the data generally showed good repeatability. The results of this study suggest that over short periods of time, the Tonopachy™ gives precise and repeatable measures of CCT and IOP. (S Afr Optom 2012 71(1)12-21)
Ray transference of a system with radial gradi- ent index
Authors: Harris W. F. 
Published: October 2016

The ray transference is central to the understanding of the first-order optical character of an optical system including the visual optical system of the eye. It can be calculated for dioptric and catadioptric systems from a knowledge of curvatures, tilts and spacing of surfaces in the system provided the material between successive surfaces has a uniform index of refraction. However the index of the natural lens of the eye is not uniform but varies with position. There is a need, therefore, for a method of calculating the transference of systems containing such gradient-index elements. As a first step this paper shows that the transference of elements in which the index varies radially can be obtained directly from published formulae. The transferences of radial-gradient systems are examined. Expressions are derived for several properties including the power, the front- and back-surface powers and the locations of the cardinal points. Equations are obtained for rays through such systems and for the locations of images of object points through them. Numerical examples are presented in the appen-dix. (S Afr Optom 2012 71(2) 57-63)