Quality performance rating

This Thesis reports on the principles and usefulness of Performance Rating as developed by the writer over a number of years. In Part one a brief analysis is made of the Quality scene and its development up to the present. The need is exposed for Performance Rating as a tool for all areas of management*. At the same time a system of Quality Control is described which the writer has further developed under the title of 'Operator Control'. This system is based on the integration of all Quality control functions with the creative functions required for Quality achievement. The discussions are mainly focussed on the general philosophy of Quality, its creation and control and that part of Operator Control which affects Performance Rating. Whereas it is shown that the combination of Operator Control and Performance Rating is both economically and technically advantageous, Performance Rating can also usefully be applied under inspection control conditions. Part two describes the principles of Area Performance Rating. *The need for, and the advantages of, Performance Rating are particularly demonstrated in Case study No.1. From this a summation expression is derived which gives the key for grouping of areas with similar Performance Rating (P). A model is devised on which the theory is demonstrated. Relevant case studies, carried out in practice in factories are quoted in Part two, Chapter 4, one written by the Quality manager of that particular factory. Particular stress is laid in the final conclusions on management's function in the Quality field and how greatly this function is eased and improved through the introduction of Area Performance Rating.

Evaluating techniques to improve visual performance with and assessment of premium intraocular lenses

Premium Intraocular Lenses (IOLs) such as toric IOLs, multifocal IOLs (MIOLs) and accommodating IOLs (AIOLs) can provide better refractive and visual outcomes compared to standard monofocal designs, leading to greater levels of post-operative spectacle independence. The principal theme of this thesis relates to the development of new assessment techniques that can help to improve future premium IOL design. IOLs designed to correct astigmatism form the focus of the first part of the thesis. A novel toric IOL design was devised to decrease the effect of toric rotation on patient visual acuity, but found to have neither a beneficial or detrimental impact on visual acuity retention. IOL tilt, like rotation, may curtail visual performance; however current IOL tilt measurement techniques require the use of specialist equipment not readily available in most ophthalmological clinics. Thus a new idea that applied Pythagoras’s theory to digital images of IOL optic symmetricality in order to calculate tilt was proposed, and shown to be both accurate and highly repeatable. A literature review revealed little information on the relationship between IOL tilt, decentration and rotation and so this was examined. A poor correlation between these factors was found, indicating they occur independently of each other. Next, presbyopia correcting IOLs were investigated. The light distribution of different MIOLs and an AIOL was assessed using perimetry, to establish whether this could be used to inform optimal IOL design. Anticipated differences in threshold sensitivity between IOLs were not however found, thus perimetry was concluded to be ineffective in mapping retinal projection of blur. The observed difference between subjective and objective measures of accommodation, arising from the influence of pseudoaccommodative factors, was explored next to establish how much additional objective power would be required to restore the eye’s focus with AIOLs. Blur tolerance was found to be the key contributor to the ocular depth of focus, with an approximate dioptric influence of 0.60D. Our understanding of MIOLs may be limited by the need for subjective defocus curves, which are lengthy and do not permit important additional measures to be undertaken. The use of aberrometry to provide faster objective defocus curves was examined. Although subjective and objective measures related well, the peaks of the MIOL defocus curve profile were not evident with objective prediction of acuity, indicating a need for further refinement of visual quality metrics based on ocular aberrations. The experiments detailed in the thesis evaluate methods to improve visual performance with toric IOLs. They also investigate new techniques to allow more rapid post-operative assessment of premium IOLs, which could allow greater insights to be obtained into several aspects of visual quality, in order to optimise future IOL design and ultimately enhance patient satisfaction.