If we continuously notice serious difficulties in carrying out our daily activities, such as reading, writing, ironing, drawing, watching television, driving a car or working on a computer, it is very likely that we have a refractive visual defect, that is, a vision abnormality.
The main vision anomalies are:
- Astigmatism
- Myopia
- Farsightedness
- Retinal diseases
- Optic nerve abnormalities
In this Psychology-Online article, we will list and define the main vision abnormalities under the theory of basic psychology.
Vision Anomalies: main eye diseases
These optical anomalies, no matter how small, cause significant discomfort that can be disproportionate when compared to the small refractive anomaly (myopia, hyperopia or astigmatism) that causes it.
Corneal abnormalities: astigmatism
A normal cornea has a constant radius of curvature. It has no equal in astigmatism. This causes parts of the object to focus well and others not. This problem can be treated, sometimes it is innate and other times it is due to mechanical injuries. Other injuries or infections produce defects, such as marks, scratches or incrustations.
retinal abnormalities
- Detachment: holes, tears and separation of the retina as a result of a blow or eye disease.
- Retinopathy: hemorrhage, oscillations in visual acuity caused by poor treatment of diabetes.
- Macular degeneration: reduced central vision, poor visual acuity, inability to discriminate colors.
- Retinitis pigmentosa: This vision anomaly is characterized by progressive degeneration of the retinal pigment layer, night blindness and poor color discrimination.
Optic nerve abnormalities
The most common nerve anomaly is its destruction or deterioration caused by glaucoma, is characterized by abnormally large pressure in the posterior chamber of the eye. The most common cause is that the aqueous humor must be renewed; if the drainage channel is occluded, the pressure rises.
Convergence anomalies
They are a product of the accommodation function performed by the lens. There are two important ones:
- Farsightedness, is characterized by a difficulty in accommodation with respect to objects located at a short distance from the individual. It is not possible to bulge enough for the image to form on the retina. The farsighted person can see distant objects well but not close ones. It may also be due to the eye being too short.
- Myopia, consists of an excess of bulging. If the object is close there is no problem. The problem is with distant objects. It can also be understood that the eye is excessively long, in which case most objects would be blurred. It can be corrected by reducing the refractive power, placing a concave lens in front, which makes distant objects closer. You can also resort to keratotomy or grinding the lens to flatten it.
The intervention of the ocular media produces blurring in the image. We could call this the point spread function. The image is sharp in the center and as we move away in any direction it becomes blurrier. This means that after the previous processes there will be others that will correct this.
How does the human eye work? – Dynamic aspects of vision
The retina is the place that contains photosensitive cells. This is where the transduction. It is composed of several layers of cells: photoreceptors, horizontal, bipolar, amacrine and ganglion. Photoreceptors are of two types: cones and rods. The cones are large and not very sensitive to light. That is why they are the cells in charge of daytime or photopic vision.
There are several kinds of cones, and each one would be characterized by being maximally sensitive to lights of a certain wavelength: 440 (blue), 530 (green) or 560 (red). This does not mean that they are not activated with other colors. There are about 8 million per eye that are concentrated mainly in the area of the retina we call the fovea. Rods are much more sensitive to light than cones. They are responsible for scotopic or night vision. There is only one type and it is maximally sensitive to intermediate wavelengths. There are about 120 million per eye.
Convergence
It consists of the fact that we have around 130 million receptors and around 10 million ganglion cells. Consequently, convergence must occur, several photoreceptors connect with a ganglion. This phenomenon raises several questions: convergence entails sensitivity, the possibility of working in minimal light conditions. We also lose resolution.
Sensitivity
It is the ability to detect minimal amounts of light. The way to ensure this is integration temporal space. If we have a non-detectable luminous point, this is added to other points that appear and affect another photoreceptor. This also occurs at a temporal level. These two sums are explained by the Ricco and Block’s Laws respectively. They come to say that the absolute threshold of luminosity of the individual within certain limits is constant for the intensity and size of the luminous point (intensity *area either intensity *duration of stimulus).
Balance Sensitivity – Resolution
There are like two subsystems, one in charge of sensitivity and the other in charge of resolution. There could be one system based on rods and the other on cones. There is evidence about both systems:
- Dark adaptation: This is based on the fact that the sensitivity changes depending on whether the environment is more or less illuminated. In the procedure the threshold is measured over time. In the graph you can see two components, which could indicate that each one corresponds to a system. If we project to an area in which there are only cones, the effect that would be produced can only be due to these.
- If we deviate the range by 20º from the fovea, the curve that would be obtained would be due only to the rods. Dark adaptation has been applied to various fields: Reading, dyslexics seem to have problems with the parafovea. These individuals’ cane system may not function properly.
- Children and some elderly people show different dark adaptation curves, the anomaly occurs with regard to canes. It is believed to be involved in seasonal affective disorder.
Vision abnormalities: The purkinje effect
We characterize this vision abnormality as follows:
- Both cones and rods are sensitive to lights of different lengths wave, but they are not sensitive in the same way.
- In low light conditions, the colors don’t look the same that with a lot of light.
- At night the only color that can be perceived well is green.
- Change the color quality when the intensity changes.
- The visual system would solve the problem by having a double system: for high sensitivity and resolution.
This article is merely informative, at Psychology-Online we do not have the power to make a diagnosis or recommend a treatment. We invite you to go to a psychologist to treat your particular case.
If you want to read more articles similar to Vision Anomalies – Basic Psychologywe recommend that you enter our category.