OTHER IMPACTS OF AMD TO VISION
This section covers some of the other impacts of AMD to vision, including:
Scotoma
An area of reduced or absent retinal sensitivity in the visual field, which is located centrally or paracentrally for patients with AMD.
Scotomas have a major impact on the performance of everyday activities and have been reported in 91% of low vision rehabilitation patients.
Wide searching motions of the eye or head can indicate a large central scotoma. A patient with a central scotoma naturally chooses (unconsciously) a preferred eccentric area of the retina to perform tasks (e.g. reading). This area is called the preferred retinal locus (PRL). Patients with a central scotoma will perform visual tasks by aiming the eye such that the image of the visual target is placed within the PRL.
AMD patients may use more than one PRL depending on the stimulus conditions or the visual task.
Patients with scotomas that encircle the PRL (ring scotomas) experience great difficulty in activities of daily living while often still having fairly good visual acuity results.
The presence or absence of a central or paracentral scotoma is a much more powerful predictor of reading problems than visual acuity.
Metamorphosia
Straight lines such as pillars or fence posts become distorted, appearing "wavy" or "bent".
Both vertical and horizontal distortions can occur, leading to difficulties in mobility and recognizing facial features.
Glare Sensitivity
Discomfort glare occurs when the overall illumination is too bright (e.g. when the midday sun is reflected from sand or snow). In extreme cases this may result in pain or photophobia. In milder cases it is often referred to as photoaversion.
Disability glare refers to the reduced visibility of a target because of the presence of a light source elsewhere in the visual field (e.g. reduced visibility of road signs in oncoming headlights).
Glare sensitivity problems increase with age. The sight of some patients with AMD will take longer than normal to adjust from bright to dim lighting, for example when going from a bright outdoor environment to a dim indoor setting, or when driving into a tunnel on a sunny day.
Steroacuity
A reduction in fine-detail depth perception experienced by patients with AMD can cause difficulties in tasks such as threading a needle or tying shoelaces.
Colour Perception
Patients with AMD may report an inability to distinguish among shades of colours.
Problems in the way colors are perceived can lead to difficulties in:
- distinguishing traffic lights
- matching clothes when dressing
- distinguishing whether fruit is ripe or meat is cooked
- decorating the home
Photopsia
The presence of formed hallucinations has been reported by over half the patients seen for low vision evaluation. This experience is not usually reported voluntarily, as patients are concerned that this may be construed as evidence that they are "losing their marbles.
Seeing faces or animals is a common experience among patients with low vision, and is typically not a manifestation of some other serious problem such as a psychiatric condition.
