Gary Philip Misson

South Warwickshire NHS Foundation Trust · Ophthalmology

The human eye can detect the polarization of light by at least two separate and distinct mechanisms: differential absorption by a radial diattenuator and polarization by scatter. Both mechanisms transform incident polarized light into luminance signals that can be detected by polarization-insensitive photoreceptors. These pre-receptoral mechanisms...

Clinical relevance: Identifying polarisation-modulated patterns may be an effective method for both detecting and monitoring macular damage. Background: The aim of this work is to determine the effectiveness of polarisation-modulated patterns in identifying macular damage and foveolar involvement using a methodology that involved feature selecti...

The relationship of macular pigments and foveal anatomy to the perception of Maxwell’s spot (MS) and Haidinger’s brushes (HB) entoptic phenomena were investigated. Dual-wavelength-autofluorescence and OCT were used to define macular pigment density and foveal anatomy in 52 eyes. MS was generated by alternating unpolarized red/blue and red/green uni...

Purpose: The purpose of this study was to determine if a battery of polarization-modulated stimuli, quantified as a single metric, is effective in identifying macular disease in the presence/absence of cataract or pseudophakia. Methods: Using a modified liquid crystal display, polarization pattern perception (PPP) for a formulated battery of geo...

O’Shea et al. review historical and modern research showing that, similar to scores of other species, humans can see the polarization of light. They describe three phenomena and how to see one of them on an LCD screen and in the sky, their mechanisms, and their clinical uses. They consider the adaptive significance of this human ability.

Many readers may know that scores of animal species sense the polarization of light for purposes including navigation, predation, and communication 1 • Horváth G. Polarized Light and Polarization Vision in Animal Sciences. Springer, 2014 • Crossref • Google Scholar . It is commonly thought that humans lack any sensitivity to polarization of lig...

In 1844, the Austrian mineralogist Wilhelm von Haidinger reported he could see the polarization of light with the naked eye. It appears as a faint, blurry, transient, yellow hourglass shape superimposed on whatever one looks at. It is now commonly called Haidinger's brushes. To our surprise, even though the paper is well cited, we were unable to fi...

Purpose: Determine the repeatability of and optimum stimulus parameters for testing polarization pattern perception in a real-world clinical population, and assess the ability of polarization perception to distinguish normal from abnormal eyes. Methods: Polarization perception was evaluated in staff and patients attending ophthalmology clinics a...

Recent reports indicate that the subjective ability of humans to discriminate between polarization E-vector orientations approaches that of many invertebrates. Here, we show that polarization-modulated patterned stimuli generate an objectively recordable electrophysiological response in humans with normal vision. We investigated visual evoked poten...

Under specific conditions of illumination and polarization, differential absorption of light by macular pigments is perceived as the entoptic phenomena of Maxwell’s spot (MS) or Haidinger’s brushes (HB). To simulate MS and HB, an existing computational model of polarization-dependent properties of the human macula was extended by incorporating neur...

Macular pigments (MPs), by absorbing potentially toxic short-wavelength (400–500 nm) visible light, provide protection against photo-chemical damage thought to be relevant in the pathogenesis of age-related macular degeneration (AMD). A method of screening for low levels of MPs could be part of a prevention strategy for helping people to delay the...

Recent studies on polarization perception have shown that humans are sensitive to patterned stimuli modulated by either angle of linear polarization (AoP) or degree of polarization (DoP). Here, we present a model of human polarization sensitivity that incorporates both AoP and DoP as spatially dependent input variables. Applying the model to both s...

Haidinger's brushes (HB) are entoptic phenomena resulting from differential absorption of linear polarized light by the human macula. Computational models have assisted in understanding the behavior of these subjective phenomena but have been limited in their application. This study presents a revised computational model that incorporates known det...

Haidinger’s brushes (HB) are entoptic phenomena resulting from differential absorption of linear polarized light by the human macula. Computational models have assisted in understanding the behavior of these subjective phenomena but have been limited in their application. This study presents a revised computational model that incorporates known det...

It is generally believed that humans perceive linear polarized light following its conversion into a luminance signal by diattenuating macular structures. Measures of polarization sensitivity may therefore allow a targeted assessment of macular function. Our aim here was to quantify psychophysical characteristics of human polarization perception us...

This study explores both theoretically and experimentally the human perception of polarized light beyond that currently established. The radial analyser theory of Haidinger's phenomenon (HP) is used to predict the effect of observing visual stimuli comprising patterned zones characterized by orthogonal planes of linear polarization (linear polariza...

A theoretical model of biaxial optical anisotropy is derived and its structural, biomechanical and developmental implications are discussed with reference to known corneal anatomy. METHODS A concise review of the theory of optical crystallography is followed by the derivation of a theoretical model of the optical anisotropic properties of a dome of...

Purpose: Optometrists are expected to refer patients with any abnormality of the eye excluding normal changes due to age to their general practitioner. It can be difficult to decide when a cataract ceases to be a normal age-related change and becomes an ocular abnormality. This study examines the criteria adopted by optometrists and GPs for referri...

A novel qualitative method is presented for determining the macroscopic distribution of collagen lamellae within the central human cornea in vivo. A modified digital photo slit-lamp camera adapted for use with circular polarised light is used. 19 eyes of 10 pseudophakic subjects (with prosthetic intraocular lens implants) are involved in the experi...

The ray transference matrix completely characterises the first-order optical nature of an optical system including the eye. It is in terms of the transference that quantitative analyses (for example, calculation of an average eye) can be performed. However, the fact that the entries of the transference do not have the same physical dimensions precl...

The theory of polarization biomicroscopy is explored using Stokes vectors and Mueller matrices. It is established that circular polarization can be used to simultaneously detect birefringent elements at any orientation unlike orientation-sensitive techniques using linear polarized light alone. A method of biomicroscopy using circular polarized ligh...

1 Abstract The theoretical aspects of the influence of optical retardation on the entoptic phenomenon of Haidinger's brushes are explored. A method is derived for the psychophysical determination of the direction and magnitude of ocular retardation along the visual axis and verified experimentally in human volunteers. The experimental method produc...

Stokes vectors and Mueller matrices are used to model the polarisation properties (birefringence, dichroism and depolarisation) of any optical system, in particular the human eye. An explanation of the form and behaviour of the entoptic phenomenon of Haidinger's brushes is derived that complements and expands upon a previous study. The relationship...

Arthur Mourant had an unusual career in which he managed to combine his first passionate interest in geology and prehistory with his subsequent medical training and interest in the geographical and racial distribution of human blood-groups. Although it was the work associated with blood-groups that was to bring him international recognition, it was...

To determine the incidence of electrophysiological abnormalities in patients with Stargardt's-fundus flavimaculatus (STGD/FFM) disease. A retrospective review was carried out of the hospital records of 46 patients who had undergone a scotopic, single flash photopic and 30 Hz electroretinogram (ERG), pattern ERG (PERG) and electro-oculogram (EOG). P...

Purpose: The phenomenon of apical total internal reflection in the cone of keratoconic patients has been described previously. This study was designed to assess the quantifiable nature of this sign and its ability to diagnose and monitor keratoconus. Method: A sample of 30 patients with varying severity of keratoconus was compared with a series of...

Optometrists are required to refer patients with any abnormality of the eye, excluding normal changes due to age, to a General Practitioner. It can be difficult to decide when a cataract ceases to be a normal age-related change and becomes an ocular abnormality. This questionnaire-based study examines the criteria adopted by Optometrists and GPs fo...

Optometrists are required to refer patients with any abnormality of the eye. excluding normal changes due to age, to a General Practitioner. It can be difficult to decide when a cataract ceases to be a normal age-related change and becomes an ocular abnormality. This questionnaire-based study examines the criteria adopted by Optometrists and GPs fo...

Purpose. To assess the efficacy of electrodiagnostic testing in predicting post operative visual outcome in a group of patients with dense lens opacities undergoing cataract extraction. Methods. Sixty-eight patients with dense lens opacities underwent electroretinogram (ERG), visual evoked potential (VEP), and uncomplicated cataract extraction. Fla...

The retinal vascular tree exhibits fractal characteristics. These findings relate to the mechanisms involved in the vascularization process and to the objective morphologic characterization of retinal vessels using fractal analysis. Although normal retinas show uniform patterns of blood vessels, in pathologic retinas with central vein or artery occ...

A retrospective study was undertaken analysing the results of trabeculectomy without antimetabolites in 33 eyes with uveitis compared to 33 eyes with primary open angle glaucoma (POAG). Both groups were matched for surgeon with a median follow-up of 19 months (range 2-44 months) for the uveitis group and 24 months (range 6-92 months) for the POAG g...

Flash and pattern visual evoked potentials were recorded in 8 patients (13 eyes) with dysthyroid optic neuropathy (DON), diagnosed using the American Thyroid Association classification. All were treated with systemic steroids, but 4 patients (6 eyes) also required orbital decompression. Flash VEP (P2) and pattern VEP (P100) were recorded prior to a...

The value of post-operative intraocular pressure (IOP) in predicting the outcome of trabeculectomy was investigated in a retrospective study of single eyes of 203 Caucasian patients with uncomplicated chronic open angle glaucoma from the Birmingham and Midland Eye Hospital. Post-operative IOPs were recorded on day 1, at 2 weeks, and at 3, 6, 12 and...

Dendritic ulcers, the commonest manifestation of herpes simplex epithelial keratitis (HSEK) are fractals. It is likely that their fractal properties alter if they progress to a geographic appearance. This study investigates the relationship of maximum ulcer diameter (Feret's diameter) to area (Dm) and perimeter fractal dimensions (Ds), parameters o...

A computer simulation of Haidinger's brushes that is based on the optics of a radially symmetrical array of dichroic elements is presented. The simulation describes the perceived distribution of intensity and contrast of Haidinger's brushes when observed with monochromatic plane polarized light at different orientations. In addition, the behaviour...

The association between peripheral astigmatic asymmetry and angle alpha was tested in the present study. Measurements were made in 34 eyes. Peripheral astigmatism was measured over the horizontal meridian using a Zeiss (Jena) Hartinger coincidence optometer and a Canon R-1 autorefractometer. Curves were fitted to the measured data of each eye and t...

The authors modeled the normally avascular mammalian cornea response to injury by neovascularization. The nature of this process remains obscure, although diffusion mechanisms are thought to be involved. Corneal neovascularization was simulated using fractal stochastic computer models for nonequilibrium diffusion (inverted diffusion limited aggrega...

The fractal dimension of the retinal vasculature and isolated venous and arterial trees down to a caliber of 40 microns was estimated in 23 routine fluorescein angiograms of normal retinas. Fractal dimension was determined with a method based on the box counting theorem. This method is less susceptible to the radial architecture of the retinal vasc...

The Pulsair 2000 non-contact tonometer (Keeler Ltd, UK) is compared with the Goldmann applanation tonometer. Data from 80 eyes were acquired by four experienced observers. A linear regression analysis showed the relationship between the instruments to be: Pulsair = 0.66 + 0.95 Goldmann. Individual components of variation were analysed by analysis o...

Nasolacrimal intubation has been advocated to obviate the need for dacryocystorhinostomy (DCR) for childhood epiphora which fails to resolve despite apparently successful probings. Twenty-eight intubations were attempted on children falling into this category. Of these, 25 were anatomically successful intubations (3 having had to be abandoned becau...

Herpes Simplex Virus (HSV) corneal ulcers have variable clinical behaviour. Classically their morphology has been (qualitatively) described as either dendritic or amoeboid. Using two techniques for fractal dimension estimation, a group of HSV corneal ulcers were analysed to determine the complexity of their shapes objectively. It was found that the...

Fractal geometry can be used to analyze the complexity and self-similarity of many natural forms and structures. By using three techniques for fractal dimension estimation, a group of 11 herpes simplex virus dendritic corneal ulcers was analyzed and found to possess outlines with fractal properties. The mean surface fractal dimension approached 1.4...

Correspondence to: Dr M. Guarro.

Total post-operative refractive astigmatism and keratometric corneal astigmatism were determined in patients following cataract surgery. By comparing the results of the two methods, the value of keratometry as a simple and quick procedure for identification of surgically induced astigmatic errors was established. It is proposed that this method sho...

Aphakic eyes possess considerably less oblique astigmatism than phakic eyes. The possibility that posterior iris displacement after lens extraction accounts for the observed reduction in oblique astigmatism is tested in this study. Oblique astigmatism was calculated for a phakic and an aphakic schematic eye. With no iris displacement little reducti...

Patients exhibiting uniocular cataract often report an improvement in vision on closing their cataractous eye. Such qualitative evidence suggests the presence of binocular inhibition--the converse of binocular summation (that is the normal superiority of binocular over monocular vision). To quantify the extent of inhibition in cataract, binocular a...

Stress-induced birefringence is used in engineering to determine the distribution of mechanical stress in experimental models. The phenomenon has previously been reported in the cat cornea but no data for the human exists. A qualitative description of stress-induced birefringence in the human cornea in vitro is presented. Circularly polarised light...