The eye is shaped as a slightly irregular hollow sphere that takes incoming light and translates it into images. Light first passes through the cornea, the clear front “window” of the eye. The cornea’s refractive power bends (refracts) the light rays that move freely through the pupil (the opening in the center of the iris) through which light enters the eye. The iris (the colored part of the eye) works like a camera shutter: it opens and closes, having the ability to control the diameter and size of the pupil and thus the amount of light entering the eye. After passing through the iris, the light rays pass through the eye’s natural crystalline lens. This clear, flexible structure works like a camera lens, shortening and lengthening its width in order to properly focus the light rays. They then pass through a dense, transparent gel-like substance, called the vitreous, which fills the eye, helping it maintain its spherical shape. In a normal eye, the light rays end up in a focus point on the retina. The retina functions much like a camera film. It is responsible for capturing all of the light rays, converting them into light impulses and then sending them to the optic nerve.
Eye movements are controlled by six pairs of muscles located on the outer part of each eye. Under normal circumstances, when both eyes look towards the same direction, one pair of muscles contracts while the other dilates. These muscle pairs function separately with the intention of keeping the eyes in parallel positions and of allowing them to move towards all directions.
When the eyes coordinate successfully
For properly functional vision, both eyes must focus on the same element simultaneously. Each eye perceives the same object from a slightly different angle, thus sending two different images to the brain, which are then combined into one unique, three-dimensional image. In a process called convergence, each eyes sees an object from slightly different angles and the brain compares and processes the two sets of information to form a single, three-dimensional image. When both eyes see clearly and the brain processes a single image effectively, it is called stereopsis.
Strabismus – Diplopia – Amblyopia
Strabismus occurs when one eye looks directly towards an object while the other eye looks to a different direction, inwards or outwards. One clear image and one blurry image are both sent to the brain from each eye respectively. These images cannot be combined into one (diplopia) and the brain chooses to ignore the image received from the weaker eye. Thus, the greatest portion of eyesight is through one eye, leaving the weak one to be used much less (amblyopia).
The eyes function fully from the age of six months old, while the brain function that perceives and processes visual stimuli grows until the age of six to seven years old.
Diagnosing visual impairment
Stereoscopic vision can be defined as the visual ability to distinguish depth; good stereoscopic vision implies that both eyes cooperate and function properly making it unlikely for strabismus or amblyopia to develop. In general, the stereoscopic vision exam is the way to diagnose and treat any visual impairment in children.
What is amblyopia?
Amblyopia is the condition that occurs when the vision of one eye deteriorates due to failure to collaborate properly with the brain. Even though the eye seems normal, the brain favors the function of the other eye.
This condition is caused by untreated strabismus; as the child grows older, the brain automatically blocks the reception of blurry images from the “weak eye”, making it idle. Consequently, amblyopia (lazy eye) is developed in the eye, making it almost blind if not treated at an early stage.
How is amblyopia caused?
Amblyopia can be developed under any condition that impedes the eye from clear focus.
- Strabismus, the inward or outward misalignment of the eyes.
- Occasionally, cataract, which causes blurriness to the front part of the eye.
- A quite common cause is the inability of one eye to focus as much as the other eye.
- Diseases related to the ability of the eye to focus light rays on the retina: farsightedness, shortsightedness and more frequently astigmatism.
Farsightedness is the condition when the distance between the cornea and the retina is too short. Such eyes tend to focus better on distance than on proximate objects.
Nearsightedness is when the distance between the cornea and the retina is too long making it easier to focus on proximate objects.
Eyes suffering from astigmatism also tend to focus with difficulty both on proximate and distant objects because of their irregular shape.
How often does amblyopia occur?
This condition is the most common cause of ophthalmological problems of children, affecting about 2 to 3 out of 100 children. Unless treated at an early childhood age it remains through adult life. Moreover, it is the most common cause for monocular diplopia amongst young and middle-aged people.
How is amblyopia diagnosed?
Unless vision in both eyes is deteriorated or the amblyopic eye is clearly irregular, diagnosing amblyopia is difficult, as children do not usually aware of a visual disfunction.
To diagnose amblyopia, the ophthalmologist examines the eyes for any possible variances by covering them in turn and by using tests to check their visual acuity. These tests vary depending on the child’s age group. For toddlers, changes in attitude are observed when each eye is covered; if the “strong” eye is covered then babies react by crying or being tense. Boards with pictures are used for younger children and boards with letters or numbers are used for older children it is. Moreover, the doctor examines the inner part of the eye to eliminate any pre-existing conditions or irregularities that might have caused amblyopia.
How is amblyopia treated?
The ophthalmologist may diagnose amblyopia in time and treat it, improving the vision. This is done with one or more of the following ways:
- Glasses prescription (if necessary). Glasses can provide good vision by fixing refractive errors. They may also treat or eliminate strabismus, for instance in the presence of high-degree farsightedness. For glasses to be prescribed (especially in the presence of strabismus), the examination is performed using special drops (cycloplegic), which nullify the eye’s natural adjustment capabilities, measuring refraction objectively. This exam can even be performed to toddlers of months of age.
- Covering the non-amblyopic eye. By covering the non-amblyopic eye with a bandage for weeks or months, the child is forced to use the eye with inferior vision. Whilst the eye is covered, children are kept busy with creative projects to increase the chances of success. Frequent ophthalmological checks are required to monitor the results.
- Eye drops such as atropine. These medications are used as an alternative form of treatment and they are applied to the non-amblyopic eye if the child is not cooperative with the eye covering method. It is used in the lighter amblyopia incidents.
- Special educative computer program (neurovision) for children of 9 years of age. This is a clinically effective treatment, which takes place at home through a computer and trains the brain into clearly recognizing images.
- Special electronic amblyopia glasses (Amblyz). This form of treatment includes a pair of glasses for children, which has a smart processor (small portable computer) and looks like a common pair of sunglasses. This processor can be programmed to adjust the polarity to create a “shutter” effect to the lens of the non-amblyopic eye. This happens for small time intervals throughout the day and strengthens the amblyopic eye. The Amblyz glasses frame is light-weight and made out of robust plastic, while the inside is covered in soft materials assuring comfortable application.
After the sight is balanced between the eyes, strabismus can be treated with surgery.
What if amblyopia treatment does not succeed?
In some cases, amblyopia treatment cannot achieve vision improvement. Choosing to interrupt the treatment is a hard decision but it is sometimes for the best. Children suffering from amblyopia in one eye may resort to safety glasses and special athletic glasses for the protection of the well-functioning eye. Given that the non-amblyopic eye stays in good condition children may enjoy any sort of activity.
Can amblyopia be treated in adults?
Given that there has not been much research conducted on adult amblyopia, the success rate for its treatment is unknown. The optical system is developed rapidly during the first 7 to 10 years of life; when the crucial connections between the eyes and the brain are created. Specialists are researching if treatment of adult amblyopia can improve the vision.
Goals of the amblyopia treatment
In all cases, the goal is to achieve the best vision possible for each eye. Even if full treatment is not always possible, a significant improvement in vision is highly possible. After the age of 9 years old, applying the eye cover method has fewer possibilities for success.
How may I assist my child in improving its vision?
As a parent, you may follow these steps:
- 1. Make sure you schedule an appointment to the ophthalmologist for your children from a young age (before 3 years old).
- 2. If needed, begin the treatment as soon as possible.
- 3. Make sure that the treatment plan is closely followed.