Vision disorders

STRUCTURE OF THE EYE

The eyeball has a diameter of about 24 mm. The eye serves functions similar to a video camera. The cornea, pupil, and lens create a sharp image of our surroundings on the retina. The lens automatically changes its shape, and the appropriate muscles change the size of the eyeball, resulting in a perfectly sharp image on the retina.

Cornea - The curved outer layer at the front of the eyeball. It helps focus incoming light. The cornea gets its nutrients from tears and fluid inside the eye. It doesn't have blood vessels and its focusing power is always the same.

Sclera - The white, protective outer layer of the eye. It keeps the eye safe from injuries and provides attachment points for the muscles that move the eyeball. The optic nerve and blood vessels pass through the back part of the sclera.

Iris - The colored part of the eye located behind the cornea. It has a hole in the center called the pupil. The iris contains muscles that adjust the size of the pupil. This helps regulate the amount of light entering the eye based on the surrounding light levels. It's an automatic process called eye adaptation.

Lens - Located behind the iris, it is a transparent, oval structure. The lens further bends light that passes through the pupil. It can change shape to focus on objects that are close or far away. This ability is called the eye's accommodation.

Retina - The inner layer of the eyeball that senses light. It contains cells called rods and cones. Rods detect light intensity, while cones help us see colors.

Macula (fovea centralis) - A small area in the center of the retina. It has the highest concentration of cones and provides the clearest vision.

Eye muscles - Six muscles on the outside of the eye move the eyeball. There are four straight muscles (superior, inferior, medial, and lateral) and two oblique muscles. These muscles work together to control eye movements and adjust the length of the eyeball.

MYOPIA (NEARSIGHTEDNESS)

Myopia is the most common vision impairment and affects nearly half of the world's population. Initially, it manifests as an inability to clearly see objects far away from us. Most often, especially when we start wearing glasses, the impairment tends to increase, on average 0.5-1 diopter per year.

Physically, it can be defined as a disproportion between the power of the optical system of the eye and the length of the eyeball. In myopia, the power of the eye's optical system is too great or the eye is too long, resulting in a blurry image of distant objects. Near objects are seen clearly by a nearsighted person.

To improve the visual acuity of a nearsighted person, diverging corrective glasses or contact lenses are used. Their optical power is expressed in diopters with a minus sign. In cases of high myopia, degenerative changes in the choroid, retina, and vitreous body may occur later in life. Myopia most often develops during adolescence.

Hyperopia (FARSIGHTEDNESS)

Farsightedness (also called hyperopia) is a vision defect caused by a disproportion between the power of the eye's optical system and the length of the eyeball. In hyperopia, the power of the eye's optical system is too weak or the eye is too short, resulting in a blurred image of objects both near and far.

Thanks to the ability of the eye's optical system to add power (accommodation), a person with hyperopia usually sees distant objects clearly, but experiences the most discomfort when working up close. Farsightedness increases with age (presbyopia) due to the progressive weakening of the eye's focusing apparatus, resulting from a decrease in the efficiency of the ciliary muscle and lens elasticity.

To improve the vision of a farsighted person, corrective glasses or contact lenses are used. These are converging lenses. Their optical power is indicated in diopters, with a plus sign (e.g., plus 3 diopters).

PRESBYOPIA (AGE-RELATED FARSIGHTEDNESS)

Presbyopia is a progressive decline in the eye's ability to change its power. It is a natural aging process of the eye and affects everyone, regardless of whether they previously had vision defects or not. People aged 40 - 45 years old begin to experience difficulty reading, especially small print, mainly characterized by the need to read in better lighting and holding the text further from the eyes.

Early presbyopia symptoms are more bothersome in the evening when the eyes are tired. This progressive process of the eye's "aging" eventually leads to an inability to read without specially designated glasses. Presbyopia can be corrected with bifocal or progressive glasses.

ASTIGMATISM (CORNEAL IRREGULARITY)

Astigmatism is a defect that causes distorted vision due to the asymmetry of the eye's cornea. If the curvature of the cornea in the vertical plane is different from that in the horizontal plane, light rays hitting different parts of the cornea are refracted to varying degrees. This causes the image seen by the patient to be blurry. It often happens that when a patient is shown a cross, they can only see one arm of it sharply - either vertical or horizontal. This type of astigmatism is called regular, and such an eye has two focal points. To correct this defect, glasses with cylindrical lenses are used. The human eye usually has physiological irregularity with a value up to 0.5D, which does not require correction. Eye injuries often cause an uneven corneal surface, resulting in irregular astigmatism, characterized by a greater number of focal points. To correct this condition, rigid (or specialized soft) contact lenses are required.

EYE CONVERGENCE PROBLEMS

In people with good vision, the eyes effortlessly focus on a given object, performing convergent movements. At short distances (e.g., reading a book), the eyes automatically turn inward to maintain a sharp image. At long distances, the eyes are virtually parallel. In a dark environment, where the pupils are wide open, the depth of field is minimal. In bright light, with small pupils, the depth of field is much larger, and we see much more sharply.

Thanks to eye convergence, we have a sense of depth and perceive the world in three dimensions. The brain automatically overlays images from each eye, creating a single three-dimensional image. If you have problems with eye convergence, you will not be able to accurately judge distances from objects. Natural convergence gradually weakens over time, often occurring alongside presbyopia, which is why it's important to regularly check for issues and start training to restore proper eye convergence if necessary. Fortunately, exercises aimed at restoring natural eye convergence yield very good results, so it's worth dedicating some time if convergence problems affect you. The most serious convergence problems occur in people with strabismus.

Eye movement in all possible directions, allowing for the observation of objects and moving objects in a broadly understood field of vision, depends on the proper functioning of the external eye muscles. Under normal conditions, both eyeballs are aligned parallel, and from the two retinal images in the visual cortex, a single image with stereopsis characteristics is created in the so-called fusion process, i.e., solid stereoscopic vision. The fusion process takes place in the visual cortex and consists of overlaying and merging two retinal images (from the right and left eye) into one with stereopsis features.

Strabismus is an abnormal alignment of both eyeballs. This is due to a lack of muscle balance with disturbed retinal correspondence or lack of binocular vision. Strabismus can cause amblyopia ("lazy eye"), which is a weakening of vision in one eye.

Depending on the direction, we distinguish several types of strabismus.:

When the eyes turn inward, it's called convergent or esotropia.
When the eyes turn outward, it's called divergent or exotropia.
When one eye looks upward, it's called upward or hypertropia.
When one eye looks downward, it's called downward or hypotropia.
When the eyes are misaligned diagonally, it's called oblique strabismus.

The most common cause, accounting for almost 50% of strabismus cases, is excessive tension in the medial rectus muscle, causing the eye to turn inward too much. The eye deviation can be minimal and almost unnoticeable or so severe that the pupil almost disappears in the corner of the eye. Since the deviation of one eye axis leads to double vision, the brain suppresses the image of the misaligned eye, resulting in reduced vision (lazy eye). Therefore, strabismus is always associated with poorer vision in one eye.

The easiest to cure is the so-called hidden strabismus, which only occurs when seeing with one eye, as binocular vision results in convergence and strabismus does not occur. Treatment methods used here mainly include exercises for improving visual convergence and balancing the defect between the eyes.

Strabismus often occurs in children but also occurs in adults. The causes of strabismus are still unknown. Usually, treatment is only provided for reduced vision if it occurs. Strabismus can be corrected using prismatic glasses that equalize divergence or surgically. However, these methods are often ineffective and lead to increasing frustration for all involved. Fortunately, natural vision training has a positive outcome rate of over 90%, significantly higher than all other optical and medical treatment methods. Children respond very quickly to vision training, so daily training for just a few weeks is usually enough.

Causes of strabismus:

Strabismus can occur in healthy eyes without a specific cause.
It can be caused by eye defects that result in poorer vision in one eye.
Some cases of strabismus are related to conditions that hinder the development of binocular vision, such as cataracts.
Strabismus can also be associated with retinal changes that affect the proper perception of visual stimuli.