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Abstract

This thesis presents a series of investigations that describe the recovery of spatial vision following a period of intense light adaptation.

The first investigation in this thesis (Chapter 2) shows, for the first time, how threshold to sinusoidal gratings (0.6-14 c.p.d.), presented in the parafovea, varies during the course of dark adaptation (30 min). For all subjects (n=7) threshold to low spatial frequency gratings declined throughout the experiment, showing discrete cone and rod limbs. For subjects with normal colour vision, threshold to high spatial frequency gratings (14 c.p.d.) increased during the ‘rod’ phase of dark adaptation, a phenomenon known as suppressive rod-cone interaction (SRCI). This increase in threshold, was not observed in the 2 protanopes studied which suggests a distil site for this interaction.

From a functional perspective, the most important quantity for the visual system to extract form the environment is contrast. Therefore, a technique has been developed for measuring contrast sensitivity (CS) during recovery from a period of intense light adaptation. Results were obtained for 2 subjects, for 5 spatial frequencies (0.6-19.9 c.p.d.) at 5 luminances (50-0.005 cdm^-2)(Chapter 3). These results provide a practical description of visual performance under such conditions.

The effect of ‘bleach’ intensity and duration on CS recovery was investigated in Chapter 4. Equal energy ‘bleaches’ that differed in intensity (I) and duration (t) (i.e. I x t = k) produced different CS recovery functions. This suggests that CS recovery is only partly explained by the concentration of a photoproduct (the photochemical hypothesis).

The effect of ‘bleach’ intensity and duration on CS recovery was investigated in Chapter 4. Equal energy ‘bleaches’ that differed in intensity (I) and duration (t) (i.e. I x t = k) produced different CS recovery functions. This suggests that CS recovery is only partly explained by the concentration of a photoproduct (the photochemical hypothesis).

To obtain a fuller understanding of how visual performance changes during photostress testing, 50 subjects were tested using a modified version of the CS recovery technique. Contrast sensitivity recovery functions were modelled using a single exponential function. Analysis of the model variables showed that the time constant of CS recovery increases with age.

The investigations presented in this thesis extend the current understanding of the recovery of spatial vision following a period of intense light adaptation.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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