Ametropia and ocular biometry in a UK university student population

Purpose. The prevalence of myopia is known to vary with age, ethnicity, level of education, and socioeconomic status, with a high prevalence reported in university students and in people from East Asian countries. This study determines the prevalence of ametropia in a mixed ethnicity U.K. university student population and compares associated ocular biometric measures. Methods. Refractive error and related ocular component data were collected on 373 first-year U.K. undergraduate students (mean age = 19.55 years ± 2.99, range = 17-30 years) at the start of the academic year at Aston University, Birmingham, and the University of Bradford, West Yorkshire. The ethnic variation of the students was as follows: white 38.9%, British Asian 58.2%, Chinese 2.1%, and black 0.8%. Noncycloplegic refractive error was measured with an infrared open-field autorefractor, the Shin-Nippon NVision-K 5001 (Shin Nippon, Ryusyo Industrial Co. Ltd, Osaka, Japan). Myopia was defined as a mean spherical equivalent (MSE) less than or equal to -0.50 D. Hyperopia was defined as an MSE greater than or equal to +0.50 D. Axial length, corneal curvature, and anterior chamber depth were measured using the Zeiss IOLMaster (Carl Zeiss, Jena, GmBH). Results. The analysis was carried out only for white and British Asian groups. The overall distribution of refractive error exhibited leptokurtosis, and prevalence levels were similar for white and British Asian (the predominant ethnic group) students across each ametropic group: myopia (50% vs. 53.4%), hyperopia (18.8% vs. 17.3%), and emmetropia (31.2% vs. 29.3%). There were no significant differences in the distribution of ametropia and biometric components between white and British Asian samples. Conclusion. The absence of a significant difference in refractive error and ocular components between white and British Asian students exposed to the same educational system is of interest. However, it is clear that a further study incorporating formal epidemiologic methods of analysis is required to address adequately the recent proposal that juvenile myopia develops principally from myopiagenic environments and is relatively independent of ethnicity.

Community-Based Study of the Association of High Myopia in Children with Ocular and Systemic Disease

Purpose. High myopia in childhood is associated with important ocular and systemic conditions. However in the UK, high myopia in early childhood is not specifically identified in current ophthalmology, optometry, or orthoptic protocols for screening, referral, or investigation. An ongoing study in the West Midlands, UK, is investigating high myopia presenting to community health care clinics with the aim of compiling guidelines for assessment and subsequent referral. Methods. Children with high myopia were identified from community optometric and orthoptic sources and invited for an ophthalmology and optometry examination to ascertain possible ocular or systemic disease. Results. High myopia with no associated ocular or systemic condition was present in 15 (56%) of the children. In seven children (25%), associated ocular problems were found including unrecognized retinal dystrophies and amblyopia. Systemic disorders associated with high myopia were found in five children (19%) and included Sticklers syndrome, Weill-Marchesani syndrome, and homocystinuria. In one child, the diagnosis made before this study was found to be incorrect, and in another child, the results were inconclusive. In two cases, the diagnosis of a systemic condition in the child led to the identification of the disease in at least one relative. Conclusions. There is a high prevalence of ocular and systemic abnormality in young children seen in the community. Optometric and ophthalmologic assessment of children less than 10 years with myopia ≥5 D is likely to identify significant ocular or systemic disease, a proportion of which will respond to medical intervention. Detection and prompt referral of these cases by community health care services may be expected to prolong vision and possibly life expectancy.

Effect of a liposomal spray on the pre-ocular tear film

Purpose: With the potential to address evaporative dry eye, a novel spray has been developed in which phospholipid liposomes are delivered to the tear film via the surface of the closed eyelid. This study evaluated the short-term effects of liposomal spray application on the lipid and stability characteristics of the pre-ocular tear film in normal eyes. Methods: Twenty-two subjects (12M, 10F) aged 35.1 ± 7.1 years participated in this prospective, randomised, double-masked investigation in which the liposomal spray was applied to one eye, and an equal volume of saline spray (control) applied to the contralateral eye. Lipid layer grade (LLG), non-invasive tear film stability (NIBUT) and tear meniscus height (TMH) were evaluated at baseline, and at 30, 60, 90 and 135 minutes post-application. Subjective reports of comfort were also compared. Results: Treated and control eyes were not significantly different at baseline (p>0.05). Post-application, LLG increased significantly, at 30 and 60 minutes, only in the treated eyes (p=0.005). NIBUT also increased significantly in the treated eyes only (p<0.001), at 30, 60 and 90 minutes. TMH did not alter significantly (p>0.05). Comfort improved relative to baseline in 46% of treated and 18% of control eyes, respectively, at 30 minutes post-application. Of those expressing a preference in comfort between the eyes, 68% preferred the liposomal spray. Conclusions: Consistent with subjective reports of improved comfort, statistically and clinically significant improvements in lipid layer thickness and tear film stability are observed in normal eyes for at least an hour after a single application of a phospholipid liposomal spray.

Neurological and ocular abnormalities in patients with Down's syndrome

Down's syndrome, first described by J. Langdon Down in 1866, is the most common chromosomal abnormality to occur in the human population. Its incidence is approximately 1/650 of all births although the risk of having a Down's child increases markedly with the age of the mother. It occurs with equal frequency in all racial groups. The risk to a mother 16-26 years old is 1 in 1,300 but the risk increases to 1 in 30 for a mother 45-47 years old. The life expectancy of people with Down's syndrome has risen since the 1920s and many individuals are now living to the 5th decade or beyond. Consequently optometrists are increasingly likley to see Down's patients of all ages in the practice.

The Human Genome Project: its relevance to ocular disease

This article describes the history of the Human Genome Project, how the human genome was sequenced, and analyses the likely impact which the results will have on the diagnosis, scientific understanding and, ultimately, treatment of ocular disease in the future.

The Rod photoreceptor ABCR gene and its significance in ocular disease

This article describes the advances in molecular genetics which have led to the discovery of the ABCR gene, the structure and possible function of the ABCR protein and the importance of this protein in ocular disease.

Genetics of ocular disease Part 1: Basic concepts: cells, chromosomes and inheritance

This series of articles describes the basic elements of genetics necessary to understand the new advances and the impact these advances will have on the study and treatment of ocular disease. The first article describes the patterns of inheritance of human characteristics, how they are transmitted between the generations and the structure of chromosomes.

Genetics of ocular disease Part 2: Basic concepts: DNA, proteins and genes

This article on the basic concepts of genetics concentrates on doeoxyribose nucleic acid (DNA), the chemical constituent of the genes. First, it will cover how DNA was discovered to be the substance of the genes. Second, the structure of DNA is revealed together with how DNA molecules can make copies of themselves. Third, the nature of the genetic code contained in DNA and how this code directs the manufacture of proteins is described. Finally, the effects of mutation of the genes and how the activities of genes are regulated will be discussed together with the relevance of these concepts to ocular disease.

Genetics of ocular disease Part 3: Patterns of inheritance of ocular disease

The objective of this article is to describe the patterns of inheritance exhibited in the human populations and to illustrate them with examples drawn from a variety of ocular diseases.

Genetics of ocular disease part 4: New developments in genetics

The objective of the final artcile in this series is to describe how recent developments in genetics are likely to imact the diagnosis, scientific understanding, and future treatment of ocular disease.

Gene therapy and ocular disease

The objective of this article is to give an overview of the history of the development and problems of gene therapy, while also considering the ethical and moral issues surrounding the application of the technology.

Ocular compatibility of hydrogel contact lenses:deposition and clinical performance

Currently over 50 million people worldwide wear contact lenses, of which over 75% wear hydrogel lenses. Significant deposition occurs in approximately 80% of hydrogel lenses and many contact lens wearers cease wearing lenses due to problems associated with deposition. The contact lens field is not alone in encountering complications associated with interactions between the body and artificial devices. The widespread use of man-made materials to replace structures in the body has emphasised the importance of studies that examine the interactions between implantation materials and body tissues.This project used carefully controlled, randomized clinical studies to study the interactive effects of contact lens materials, care systems, replacement periods and patient differences. Of principal interest was the influence of these factors on material deposition and their subsequent impact on subjective performance. A range of novel and established analytical techniques were used to examine hydrogel lenses following carefully controlled clinical studies in which clinical performance was meticulously monitored. These studies established the inter-relationship between clinical performance and deposition to be evaluated. This project showed that significant differences exist between individuals in their ability to deposit hydrogel lenses, with approximately 20% of subjects displaying significant deposition irrespective of the lens material. Additionally, materials traditionally categorised together show markedly different spoilation characteristics, which are wholly attributable to their detailed chemical structure. For the first time the in vivo deposition kinetics of both protein and lipid in charged and uncharged polymers was demonstrated. In addition the importance of care systems in the deposition process was shown, clearly demonstrating the significance of the quality rather than the quantity of deposition in influencing subjective performance.

Ocular biomaterials and the anterior eye

Hydrogels, water swollen polymer matrices, have been utilised in many biomedical applications, as there is the potential to manipulate the properties for a given application by changing the chemical structure of the constituent monomers The eye provides an excellent site to examne the interaction between a synthetic material and a complex biological fluid without invasive surgery. There is a need for the development of new synthetic hydrogels for use in the anterior eye, Three applications of hydrogels in the eye were considered in this thesis. For some patients, the only hope of any visual improvement lies in the use of an artificial cornea, or keratoprosthesis, Preliminary investigations of a series of simple homogeneous hydrogel copolymers revealed that the mechanical properties required to withstand surgery and in eye stresses, were not achieved This lead to work on the development of semi-interpenetrating polymer networks based on the aforementioned copolymers, Manufacture of the device and cell response were also studied. Lasers have been employed in ocular surgery to correct refractive defects. If an irregular surface is ablated, an irregular surface is obtained. A hydrogel system was investigated that could be applied to the eye prior to ablation to create a smooth surface. Factors that may influence ablation rate were explored, Soft contact lenses can be used as a probe to study the interaction between synthetic materials and the biological constituents of tears. This has lead to the development of many sensitive analytical techniques for protein and lipid deposition, one of which is fluorescence spectrophotometry. Various commercially available soft contact lenses were worn for different periods of time and then analysed for protein and lipid deposition using fluorescence spectrophotometry, The influence of water content, degree of ionicity and the lens material on the level and type of deposition was investigated.

Lipoidal species in ocular spoilation processes

Tear component deposition onto contact lenses is termed `spoilation' and occurs due to the interaction of synthetic polymers with their biological fluid environment. Spoilation phenomena alter the physico-chemical properties of hydrophilic contact lenses, diminishing the optical properties of the lens; causing discomfort and complications for the wearer. Eventually these alterations render the lens unwearable. The primary aim of this interdisciplinary study was to develop analytical techniques capable of analysing the minute quantities of biological deposition involved, in particular the lipid fraction. Prior to this work such techniques were unavailable for single contact lenses. It is envisaged that these investigations will further the understanding of this biological interfacial conversion. Two main analytical techniques were developed: a high performance liquid chromatography (HPLC) technique and fluorescence spectrofluorimetry. The HPLC method allows analysis of a single contact lens and provided previously unavailable valuable information about variations in the lipid profiles of deposited contact lenses and patient tear films. Fluorescence spectrophotofluorimetry is a sensitive non-destructive technique for observing changes in the fluorescence intensity of biological components on contact lenses. The progression and deposition of tear materials can be monitored and assessed for both in vivo and in vitro spoiled lenses using this technique. An improved in vitro model which is comparable to tears and chemically mimics ocular spoilation was also developed. This model allows the controlled study of extrinsic factors and hydrogel compositions. These studies show that unsaturated tear lipids, probably unsaturated fatty acids, are involved in the interfacial conversion of hydrogel lenses, rendering them incompatible with the ocular microenvironment. Lipid interaction with the lens surface then facilitates secondary deposition of other tear components. Interaction, exchange and immobilisation (by polymerisation) of the lipid layer appears to occur before the final and rapid growth of more complex, insoluble discrete deposits, sometimes called `white spots'.