A qualitative exploration of the effect of visual field loss on daily life in home-dwelling stroke survivors.

OBJECTIVE: To explore the effect of visual field loss on the daily life of community-dwelling stroke survivors. DESIGN: A qualitative interview study. PARTICIPANTS: Adult stroke survivors with visual field loss of at least six months' duration. METHODS: Semi-structured interviews were conducted with a non-purposive sample of 12 stroke survivors in their own homes. These were recorded, transcribed verbatim and analyzed with the framework method, using an inductive approach. RESULTS: Two key analytical themes emerged. 'Perception, experience and knowledge' describes participant's conflicted experience of having knowledge of their impaired vision but lacking perception of that visual field loss and operating under the assumption that they were viewing an intact visual scene when engaged in activities. Inability to recognize and deal with visual difficulties, and experiencing the consequences, contributed to their fear and loss of self-confidence. 'Avoidance and adaptation' were two typologies of participant response to visual field loss. Initially, all participants consciously avoided activities. Some later adapted to vision loss using self-directed head and eye scanning techniques. CONCLUSIONS: Visual field loss has a marked impact on stroke survivors. Stroke survivors lack perception of their visual loss in everyday life, resulting in fear and loss of confidence. Activity avoidance is a common response, but in some, it is replaced by self-initiated adaptive techniques.

A device for the relief of phantom limb pain and rehabilitation in stroke.

PURPOSE: To determine if simple, robust spectacle mounted devices are feasible for the replacement of the mirror boxes currently used in the rehabilitation of patients suffering from phantom limb pain, complex regional pain syndrome and stroke. METHODS: Four devices, using three different optical systems were produced: plane mirror, astronomical telescope using cylindrical lenses and two reflecting prism systems. RESULT: The illusory effect of the devices was similar to that of the mirror box. CONCLUSIONS: Any of the systems would be suitable to replace the mirror box, but the reflecting prism system is the easiest to set up.

The weight of spectacle frames and the area of their nose pads.

The current international standard for spectacle frames recommends that frames weighing up to 25 g should have a minimum nose-pad contact area of 200 mm(2) and that those weighing over 25 g should have a minimum contact area of 250 mm(2). It is shown that these recommendations are being almost universally ignored for frames with separate pads on arms. The information on frame materials in manufacturers' literature is woefully inadequate but, from the information available, there was little difference in weight between stainless steel frames and those from unnamed materials.

Low energy lamps and eye lens autofluorescence.

Tungsten filament lamps are rapidly being displaced from the market-place by compact fluorescent lamps. Although the colour temperature and total luminous output of a fluorescent lamp may be similar to that of an incandescent lamp, the output spectrum is very different. The peaks of the mercury vapour spectrum at 365.4nm (UV) and at 435.8nm (blue) are close to the peak fluorescence excitation wavelengths in the human lens, and it has been shown that such fluorescence can lower sensitivity to low contrast objects. This effect could also explain the reported preference for brown, red and yellow tinted lenses often reported by elderly patients, as these coincidentally block the ultraviolet and blue exciting wavelengths.

The influence of automobile windscreen rake on effective light transmittance.

The theoretical transmittances at the installation angle of the windscreens of the ten best-selling cars in the UK in 2008 are investigated. The data show that the ten most popular cars on the UK roads have a windscreen rake that reduces transmittance to a value close to or below that specified in International Standards for normal incidence. British and International Standards for windscreen transmittance should be revisited by the relevant authorities in the light of the high rake angles that have become widespread in recent years. The problem is worsened considerably by tinted windscreens having become the default option in many models. It is also suggested that there may be good reason for all spectacles supplied to drivers for low light level driving to be untinted and anti-reflection coated.

Automobile windscreen rake, spectacle lenses, and effective transmittance.

PURPOSE: To investigate the effect of windscreen rake angle on effective transmittance and the contribution of spectacle lenses to the total transmittance of the system. METHODS: Theoretical analysis has been carried out using the Fresnel reflectance equations. RESULTS: Windscreen rake can reduce effective transmittance significantly at angles present on modern aerodynamic vehicles. Spectacle lenses reduce the total transmittance still further, often to below the minimum level permissible in current international standards for windscreens. CONCLUSIONS: Drivers should always be supplied antireflection-coated lenses where there is a chance of their spectacles being used for night-time driving, if current International standards for windscreen transmittance are to be met by the spectacle-windscreen combination. Windscreen rake angle should be accounted for both in the International Organization for Standardization transmittance standards and in roadside testing devices.

Vertical diplopia on downgaze with bifocals.

PURPOSE: To investigate if jump or diplopia is experienced at the dividing line of bifocal lenses and if the belief in jump may be, in part, the result of leading questions. METHODS: Ten subjects were asked an open question and 10 a closed question relating to jump for six bifocal lenses and three eye movement conditions. RESULTS: All subjects failed to see any effects other than near blur with saccadic movements. Many subjects observed vertical diplopia with round 38 segments at the bifocal edge during pursuit movements given an open choice of responses. With pursuit movements, when asked a closed leading question, all subjects saw jump with 38 round segments and approximately 50% saw jump with C28 segments. CONCLUSIONS: Bifocal "jump" is shown to be diplopia if an open question is asked of subjects. This is as would be predicted from simple geometrical optics. Both jump and diplopia are shown to be difficult to perceive with C segment and E-style lenses, even though theoretically present. The relevance of diplopia, as opposed to jump, in adaptation to bifocals is considered.

Optical dispensing: the science of vision or blind faith?

The evidence for the basic optometric function of optical dispensing is discussed in terms of the basic principles of scientific debate. The degree of rigour applied to product testing and evaluation of most other medically related areas is lacking in the dispensing of spectacles. There has been much debate on the place of religious faith in our society. Religious belief masquerading as science has come in for particular scrutiny. However, little attention has been paid to the equally contentious issue of non-religious belief, within scientific disciplines, masquerading as science. It could be argued that optical dispensing is, to a significant degree, such a case.

Does the niqab (veil) wearer satisfy the minimal visual field for driving?

Visual field testing of subjects wearing a niqab was carried out using the approved (Esterman) test on a Humphrey perimeter to determine if visually normal subjects met the European driving standard. Measurement of aperture dimensions of the niqab when worn was recorded. When wearing the niqab, all subjects achieved a visual field adequate to satisfy UK/European driving standards. A measurement of the limiting aperture size was obtained and a self-test method for niqab wearers was determined.

A simple variable prism with a linear scale.

PURPOSE: To build a simple, low cost, variable-power prism with a linear scale. METHODS: A sliding lens system, using the prismatic effect of ophthalmic lenses, was constructed. RESULTS: The system functions well at low powers using conventional curved form ophthalmic lenses. CONCLUSIONS: The sliding lens variable prism is a useful alternative to the conventional rotating variable-power prism.

Materials and allergens within spectacle frames: a review.

The materials that have been reported as causing allergic contact dermatitis within spectacle frames are identified, and their most likely location on the frame is highlighted. The lack of any real control over spectacle frame quality and content is indicated to be a problem, as is the difficulty in determining the true source of many frames. Much of the information must be obtained from anonymous sources in the industry, historical 'common knowledge' of indeterminate source or reports of dermatological problems.

A simple new method for the construction of a ptosis crutch.

A technique by which a ptosis crutch can be fitted in minutes, using readily available and inexpensive materials and tools, is described. No specialist skills are needed and the device can be fitted to existing frames and lenses.

Is the spectacle lens jack-in-the-box phenomenon really due to the lenses?

The calculation of the extent of the ring scotoma around positive lenses, as conventionally taught to students of clinical optics, indicates that the scotoma is of a significant size. Using knife-edge lenses this study shows that the calculations are invalid due to the finite size of the eye's entrance pupil and in many instances the scotoma is shown not to exist. The effect noticed in clinical practice is probably largely due to the frame and the edging techniques used which add to the refractive scotoma which is present with high powered lenses, large apertures and/or small pupil sizes.