Visual system concepts and definitions

Prof. Kent Caszlo, Professional Director of the Israel ALE.
Eye structure

Cornea cornea

  • Transparent dome-like structure
  • First and outer layer of the eye
  • Transmits flares from the object into the eye

Iris iris

  • Located behind the corneal and in front of the lens.
  • Gives the characteristic color of the eye
  • At the center of it is the pupil.
  • Responsible for shrinking and expanding the pupil.
  • The iris lyses the amount of incoming light and contributes to the sharpness of vision (noir phenomenon).

Pupil – Pupil

  • A hole in the center of the iris. We think it's black because light doesn't come out of it.
  • Determines the amount of light that enters the eye and reaches the ret.
  • Its function is similar to reducing the camera:
  • In the dark, the pupil expands.
  • In the light the pupil shrinks.

Lens lens

  • Located behind the pupil.
  • Made of transparent elastic tissue.
  • Its function is to break another of the rays of light that pass through the lens, thus concentrating on one focus that falls on the retina.
  • The lens is dynamic and strengthens for close vision and returns to zero state for distant vision


  • The inner part of the eye is composed of cells (receptors) and nerve fibers, their function is to absorb the rays of light that have passed through all parts of the eye and transmit the information to the brain.
  • The energy of light becomes the same electricity that passes through the optic nerve to the brain.

The receptors

The main cells in the retino are called receptors, there are two types, rhodes in the form of cane and cones in the form of a cone.
The receptors absorb the light and transmit an electrical message to the brain (not images).
The most important difference between them is:

  • Cones can report details, central vision, colors and day vision
  • Harrods reports peripheral (general) and night vision.

The Macula

  • The macula is responsible for the central vision and its center is called the phobia. Physically, it's about 2% of the entire ret right.
  • This area is responsible for sharp vision, color vision, detail vision, reading and facial recognition.
  • Outside the macala in the retina area – responsible for peripheral vision and night vision. This area is very much about getting around space

Main Eye Track – Visual Brain
At least
40% of the brain is directly involved in the visual process, with new studies suggesting about 90% of the brain is involved.

Why is it important to have a quick maturity of the visual system?

  • The sense of sight leads us further and more accurately than any other sense.
  • To enable the development of motor movements under visual supervision
  • Damage to the sense of vision affects the entire motor development of the baby in addition to the effect on visual perception.

The connection between the brain and the eye develops and strengthens due to the quality of the message that the eye transmits. At the beginning of the development of the visual system, the reporting to the brain is that of each eye separately – there are cells that receive a report from the right eye and cells that receive a quasi-left report of equal quality. Later in the reporting of two eyes merges in cells that absorb reports from both eyes together ("bi-eyed" cells). In a state of equality between the eyes, the "competition" between them ends in a "draw" and both eyes are connected to the "bi-poor" cells in equal measure.
This is the basis for 2D and 3D vision
In a state of visual impairment, when there is an impairment of the quality of vision in one eye (or both), the message that passes from the eye to the brain is not of quality, the connection is weakened and therefore there will be an effect on communication and connection to the brain.
For example, if the message of one kind is wrong due to blurred vision, a lazy eye (ambliophy) may develop, which is poor vision even if you lower the cause of blurring (such as cataracts) or if glasses are suitable.
If the message from the eye is wrong due to strabismus, there is the chance of two problems:

  • Difficulty in bi-ocular vision: In competition in the brain for the "two-eyed" cells one eye will win, "conquering" most (or all) of the bi-eyed cells.
  • Lazy eye: impaired vision in the same eye even if the eclipse is taken down/corrected

In both cases, although the problem begins with the phenomenon in the eye, the real problem is in mind-eye communication.
Echomadation of the lens
chomedation – Focusing the lens of the eye by changing the lens constellations as a result of contracting the muscles that surround it.
The echomadation of the eye lens allows the person to see sharply as he looks at different distances.
When we look at a distant object, the focus of the rays on their way to the retino is mostly done in the corneal, so the lens can be relatively flat. But when we look at a close object, further breaking and focus is needed by the lens.

Hyperopia Sight-Impaired

When the rays of light come out of a close spot, they do not concentrate on the retina but behind it, so that the person cannot clearly see nearby objects.
Distant objects are relatively clearly visible.
Farsightedness may be caused by a short eyeball, or due to the non-acumness of the corneal or due to poor lens shape. It's usually a birthing eclipse.
Myopia myopia myopia

A state of impairment in the break of the rays of light caused by the lens's inability to concentrate the light on the retina of the eye.
Myopia manifests itself in the focus of the observed bone before the retina. Therefore, nearby objects are clearly visible, while distant objects appear blurry.
The strength o
f our eye should be symmetrical, so a lot of people with glasses have a "number" that corrects them (such as +2.00 or -4.00). In astigmatism, the eye has two forces on different planes (sometimes comparing it to the difference between a ball and an egg, even though the eye never looks like an egg). Correct it by repairing two forces on different planes (cylinder) and then having a prescription for more complex glasses, such as + 2.00-1.00X180
Eye movements
hese movements reach a good level very early in the baby's life.

  • Sight surveillance or pursuit

– The purpose of this movement is to "perceive" the character with the center of vision to get more content and understanding
– Begins to exist at 3 months of age and improves greatly until the age of 4 months when we expect 80% of an adult's ability.

  • Saccades: Transactions used to "scan" space and also in reading

– Starts around a month
– Reaches 70% adult ability at six months of age
These two movements are functi
ons of the central visual system.
Biocular vision

  • The ability to combine two eyes together begins around the age of 3 months.
  • The most sensitive period for the development of 3D vision ends around the age of 3
  • In many cases it is difficult to determine that there is strabismus before the age of six months (there is still the possibility of independent actions of the eyes in normal newborns)
  • Any strabismus prescribed until the age of 12 months is defined as the strabismus of the newborn.

What's the field of view?

  • The amount of peripheral vision around the center of the gaze
  • The field of view is measured in degrees and is angular
  • There is overlap in a field of view of two eyes

Visual acuity
Visual acuity is angular and there are different types of visual acuity:

  • Light perception
  • Light Projection
  • Discrimination
  • Form vision or recognition
  • Separation Capacity, Resolution (Resolution)
  • Localization (localization)
  • Super capabilities

Visual acuity develops quickly and at the age of six months it is very ripe and therefore it is of high importance for therapeutic intervention very early in the baby's life.

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