Analysis of light visual distortion and quality of vision with different multifocal lens designs for the compensation of presbyopia

Resumo

The present Thesis integrates the results of the studies conducted at the Clinical & Experimental Optometry Research Lab – Minho University (CEORLab) and in collaboration with hospital and clinics that were interested in knowing how we can quantify the sensations that the patients normally describe when using optical devices that change their quality of vision under certain conditions, as night time conditions. In the second chapter of this thesis, we initially explain Night Vision Disturbances (NVD) in the form of haloes, glare, and starburst that affect many subjects when viewing under dim illumination conditions. First, we tried to define several terms relating to this topic due to a lack of standardization. Next, and due to lack of scientific validity of some tests, there were explained how some of them work and why they are sometimes hard to interpret by the physician and by the patient. In chapter 3, we conducted measurements with the new prototype device Light distortion Analyzer (LDA) in a series of subjects to evaluate the repeatability of the prototype device under different conditions of brightness of the stimuli, pupil size, and different examination strategies previously configured in the software of the device. Simultaneously, the times of examination were recorded in order to determine if they are feasible in the clinical practice. One of the goals of the present thesis, resulting in chapter 4, was to apply the measurement of disturbances in contact lens wearers. To test this, two different contact lens materials were fitted to subjects and the light disturbances were measured under different blinking intervals. This work concluded that the perception of light disturbance is affected by the frequency of blinking and this effect worsens with contact lenses. However, under frequent blinking it is not expected that the contact lens material do play a role in the measurement of light disturbance. Chapter 5 reports the results of a study that investigated the impact of different multifocal contact lens (MFCLs) designs in the perception of light disturbance. The multifocal contact lenses produce multiple simultaneous foci that can compromise the quality of the images viewed by the subjects, especially under night vision conditions. The device used to measure night vision disturbances NVD, the Light Distortion Analyzer (LDA), showed to be sensitive to differences in the patterns of disturbance generated by multifocal systems. Besides quantifying NVD, subjective assessment of patient’s complaints was measured by means of two questionnaires in chapter 6. We compared for three different multifocal soft contact lenses worn by presbyopic patients for a 15 days period, using the LDA to quantify the NVD and the questionnaires to know more about the subject’s subjective perceptions. NVD can be can be exacerbated by certain ocular conditions, such as cataract, and refractive surgery procedures. To understand the quality of vision of patients implanted with Multifocal IOL’s, it is important to analyse not only visual acuity and contrast sensitivity, but also try to examine the disturbance caused by punctual sources of light under night vision conditions. The purpose of chapter 7 was to evaluate the light disturbance after refractive lens exchange (RLE) with diffractive bifocal and trifocal intraocular lenses (IOLs) in comparison to a monofocal procedure. Outcome measures showed the reliability of the Light Distortion Analyser (LDA) in finding increased light disturbance index (LDI) in the multifocal groups, as a result of the diffractive optics systems of the current lenses. The perceptions of the patients involve much more factors than the optical ones measurable in the optical bench, as it was study in Chapter 8. However, this experiment confirms that the perception measured with LDA depends in part of the optical design of the lens and its physical performance, as might be anticipated.