Ocular Aberrations Wavefront Sensor in Clinical Application

A versatile Hartmann-Shack (HS) wavefront sensor (WFS) was designed and constructed. Its advantages include simultaneous pupil centre determination, off-axis capability, realtime data displays, and efficient lenslet sampling orientation. The instrument is compact and transportable, making it convenient for use in a clinical setting. Subject alignment is achieved by the use of a parallel channel that is recombined with the sensing channel to simultaneously image the external eye and the HS spots onto a single charge coupled device (CCD). The pupil centre is determined using this image of the eye, rather than the HS spots. Off-axis measurements are possible throughout an unobstructed 10 degree field of view. User-friendly software was developed to provide the clinician with data displays at 10 Hertz and above. The optical design includes a rotated lenslet array which increases the dynamic range in those meridians where astigmatism is most typically expected in the eye. Telecentric re-imaging of the HS spots increases the system’s robustness to CCD misalignment. Our experimental WFS was used in two experiments. The first experiment examined agreement between the experimental WFS and the ZyWave (a commercially available WFS) for monochromatic aberrations measured on 21 normal eyes. The second experiment investigated the variation of monochromatic aberrations over the central visual field. Measurements were performed on 60 normal eyes and the data was used to produce a statistical model of population distributions of Zernike coefficients. It is hoped this data will aid future designs for ocular multi-conjugate adaptive optics systems endeavouring to achieve wide-field high resolution retinal images

Optical characterisation of holographic diffusers and Bangerter foils for treatment of amblyopia

Amblyopia is a significant issue for children worldwide, and current treatment methods have drawbacks that can hinder treatment effectiveness and/or patient experience. This study proposes a new treatment method using holographic diffusers while also comparing their optical characteristics to a current treatment method (Bangerter foils). Holographic diffusers were developed by optically patterning thin polymer layers on a micron scale. Two compositions of photopolymer (acrylamide and diacetone acrylamide based) are analysed herein. Characterisation shows that holographic diffusers of either composition can achieve a wide range of on-axis intensity reductions, allowing for precise and customisable treatment levels by altering recording exposure time in a low-cost and durable manner

Compliance and Appropriateness of Driver Vision Regulations in Ireland

Driving is a highly complex task which relies heavily on vision for successful execution. There are currently 2,820,528 holders of driving licences in Ireland. Holders of a driving license must meet the standards for vision as set out by the Road Safety Authority Slainte agus Tiomáint document. Visual acuity and Visual Field measurements are specified as the minimum standard. If there is reason to believe that these measurements are inadequate, it is required that the subject undergo a more detailed examination. Currently, drivers must undergo a vision screening when applying for their first license, and additional vision screening is not required until they reach 70 years of age. During this interval, licenses have 10 yearly renewal intervals. It is well known that a person’s vision changes with age. These changes may be normal and age-related, or pathological and disease related. Either Way, these changes can have a significant detrimental effect on both unaided vision and corrected acuity, and therefore their ability to meet the driving standards (either with or without refractive aides). It is our aim to assess the vision of a sample population of drivers with respect to the current vision standards for driving, and to critically evaluate the appropriateness of the standards currently in place

Modelling spherical aberration detection in an analog holographic wavefront sensor

The analog holographic wavefront sensor (AHWFS) is a simple and robust solution to wavefront sensing in turbulent environments. Here, the ability of a photopolymer based AHWFS to detect refractively generated spherical aberration is modelled and verified

Analog holographic wavefront sensor for defocus and spherical aberration measurement recorded in a photopolymer

An analog holographic wavefront sensor (AHWFS), for measurement of low and high order (defocus and spherical aberration) aberration modes has been developed as volume phase holograms in a photopolymer recording medium. This is the first time that high order aberrations such as spherical aberration can be sensed using a volume hologram in a photosensitive medium. Both defocus and spherical aberration were recorded in a multi-mode version of this AHWFS. Refractive elements were used to generate a maximum and minimum phase delay of each aberration which were multiplexed as a set of volume phase holograms in an acrylamide based-photopolymer layer. The single-mode sensors showed a high degree of accuracy in determining various magnitudes of defocus and spherical aberration generated refractively. The multi-mode sensor also exhibited promising measurement characteristics and similar trends to the single-mode sensors were observed. The method of quantifying defocus was improved upon and a brief study into material shrinkage and sensor linearity is presented

Direct multiplexing of low order aberration modes in a photopolymerbased holographic element for analog holographic wavefront sensing

The fabrication of an analog holographic wavefront sensor, capable of detecting the low order defocus aberration, was achieved in an acrylamide-based photopolymer. While other implementations of holographic wavefront sensors have been carried out digitally, this process utilises a recording setup consisting only of conventional refractive elements so the cost and complexity of holographic optical element (HOE) production could be much reduced. A pair of diffraction spots, corresponding to a maximum and minimum amount of defocus, were spatially separated in the detector plane by multiplexing two HOEs with different carrier spatial frequencies. For each wavefront with a known aberration that was introduced during playback of the hologram, the resulting intensity ratio was measured in the expected pair of diffracted spots. A number of HOEs were produced with the diffraction efficiency of the multiplexed elements equalized, for a range of diffraction efficiency strengths, some as low as \u3c5%. These HOEs were used to successfully classify four amounts of the defocus aberration through the observed intensity ratio

Mind the Gap: Integration of International Students

The international mobilisation of tertiary students is increasing from 0.8 million in 1975 to 3.5 million worldwide by 2016 (OECD, 2018). This increasingly fluid student migration, supported with various European initiatives, the Erasmus exchange program (since 1987) and the Bologna Declaration (since 1999), have influenced the profile of students within the Irish higher education system. By 2016, international students comprised 5.1% of total tertiary students in Ireland (OECD, 2018). According to Irish and UK research, lecturers have an important role in facilitating integration (British Council, 2014; Irish Council for International Students, 2017). However, for most faculty, the term internationalisation of the curriculum was unfamiliar (Clarke, Hui Yang & Harmon, 2018) and faculty also had mixed views on a need to explicitly address cultural and language issues in their learning outcomes or assessment tasks. Although some faculty viewed intercultural training as important most had not received this kind of support (Clarke et al., 2018). This report focuses on the integration challenges international students face, and what best-practice recommendations are available to assist lecturers in aiding integration

Population Study of the Variation in Monochromatic Aberrations of the Normal Human Eye Over the Central Visual Field

Abstract We present data analysis for ocular aberrations of 60 normal eyes measured with a Hartmann-Shack (HS) wavefront sensor (WFS). Aberration measurements were made on-axis and at 5 degree field angles in the nasal, inferior, temporal and superior semi-meridians. Particular attention is given to aberration distributions and possible strategies for aberration correction are discussed. A versatile HS WFS was designed and constructed with features of simultaneous pupil centre determination, off-axis capability, real-time data displays, and efficient lenslet sampling orientation. The subject alignment is achieved by the use of a parallel channel that is recombined with the sensing channel to simultaneously image the eye and the HS spots onto a single CCD. The pupil centre is determined using this image of the eye (iris edge), rather than the HS spots. The optical design includes a square lenslet array positioned with its diagonals aligned with the most typical principal astigmatic meridians of the eye. This favourable orientation helps to enlarge the dynamic range of the WFS. The telecentric re-imaging of the HS spots increases the robustness of the system to defocus in the event of CCD misalignment

Teenagers, Technology, and Education at the CCVC

This report is a culmination of research and analysis gathered to contribute to alternative ways of teaching at the Caritas Charles Vath College (CCVC), secondary school in Hong Kong. This project examined the possibility of using technology in the classroom to increase student interest and motivation in learning. The report concluded that technology would not be an effective solution for the CCVC at this time and it was recommended that more attention be directed towards student discipline and learning difficulties