AGE-RELEATED FEATURES OF

SENSORY SYSTEMS (ANALYZERS)

National University of Pharmacy

Human anatomy and physiology department

EYES

and

VISION

Plan

1. General principles of the structure of sensory systems.

2. Properties of analyzers.

3. The structure of the eye, its departments, functions.

4. The structure of the visual sensory system.

5. Age features of vision in children of different age

groups and elderly people.

6. Accommodation, importance and development with

age, disruption of accommodation (nearsightedness and

farsightedness).

One of the most important functions of the nervous system is obtaining

and analyzing information about changes in the conditions of the

external and internal environment. This function is performed by the

nervous system with the help of analyzers.

THE CONCEPT OF ANALYZERS

ANALYZER – a single functionally and

anatomically related system consisting of a

receptor apparatus located on the periphery of

afferent neurons, conducting pathways and

various parts of the cerebral cortex (according to

I.P. Pavlov)

Analyzers consist of three parts:

1. The peripheral part of the analyzer, where the perception

(reception) is present. This part is represented by nerve cells

that perceive irritations. Depending on the nature of the

stimulus, photoreceptors, mechanoreceptors, nociceptors,

chemoreceptors, thermoreceptors, are distinguished.

There are organs of vision, hearing, taste, smell, touch and balance.

2. An intermediate part formed by the conductive pathways and

subcortical structures.

3. A central part – plot of the cerebral cortex, where the analysis

and synthesis of the final of perceived sensations.

THE CONCEPT OF ANALYZERS

Eye and visionThe organ of vision is the most

important of the sense organs,

providing a person with up to 90%

of information. Peripheral part of the

analyzer – the organ of vision

consists of the eyeball and auxiliary

organs: eyelids, eyelashes, lacrimal

glands, oculomotor muscles.

The wall of the eyeball consists of

three membranes.

1. SCLERA, in the anterior part of

the eye is transparent, this part of it

is called the cornea.

2. CHOROID (vascular membrane ).

In the anterior part it passes into the

iris, which has a hole in the center –

the pupil. The annular and radial

muscles of the iris reflexively

change the diameter of the pupil,

regulating the amount of light

entering the eye. The color of the

eyes depends on the pigment of the

iris.

Eye and vision

Eye and visionNear the iris is the ciliary body, the muscle, through which the

curvature of the lens changes, accommodation takes place, an

adaptation to a clear vision of objects located at a different distance

from the eye.

Between the cornea and the iris is a cavity filled with humor – the

anterior chamber of the eye. The cavity between the iris and the lens is

called the posterior

chamber of the eye.

3. RETINA. It contains photosensitive

cells – visual receptors, about 130

million rods, providing a black-and-

white vision and about 7 million cones

giving information about color.

The retina consists of several layers of cells: the outer layer adjacent to

the choroid is a layer of black pigment cells. This layer absorbs light,

preventing its dispersion and reflection. Then there is a layer containing

rods and cones, in front of it there are three more layers of cells, then

their axons uniting into the optic nerve.

Eye and vision

Eye and visionThe maximum number of cones is in the retina at the optical axis of

the eye, against the pupil, this area is called the yellow spot. In the

place where the optic nerve departs from the eyeball, there are no

receptors in the retina – a blind spot. The maximum number of rods is

located on the periphery of the eye. Rods contain visual pigment

rhodopsin, cones – Iodopsin

The vitreous body fills

the whole cavity of the

eye, is formed by a

transparent gelatinous

substance. Between the

vitreous body and the

posterior chamber of

the eye is the lens, an

elastic transparent

formation in the form of

a biconvex lens.

Anatomy of the Eyeball

How do we see?Light passes through the cornea,

that bends – or refracts – this incoming

light. The iris regulates the size of the

pupil, the opening that controls the

amount of light that enters the eye.

The lens further focuses light, or an

image, onto the retina. The image on

the retina is reduced and inversed.

The photoreceptors of retina convert

light into electrical signals. These

electrical signals are processed further,

and then travel to the brain (posterior

parts of the occipital lobes) through the

optic nerve.

The brain processes the signals and

again flips the image and we see

everything correctly.

Age features of the visual analyzerIN A NEWBORN

There is no complete morphological maturity of all

parts of the analyzer.

The image on the retina is inversed.

Gradually, due to the activity of the cortical part of the

analyzer, the perception of the direct image is formed.

This period is reflected in the fact that in the first

months of life the child confuses the upper and lower

sides of the subject.For example, if a child is shown a burning candle, trying to grab

a flame, he will stretch his hand not to the upper, but to the

lower end of the candle.

The pupil is narrow – no more than 3 mm in diameter,

at 6-8 years it becomes wide, because during this

period the sympathetic fibers begin to exert a tonic

effect on the muscle that widens the pupil.

Eye coordination in a newborn is imperfect:

movements are jerky; periodically there can be

a convergent strabismus (cross-eyed).

Effective coordination is achieved by 3-7 years.

Protective reflexes

Blinking appears in the first days of life, but

the blinking rate is lower (2 times per 1 min)

than for an adults (20 times per minute).

The lacrimal reflex appears at the 2nd month;

before this time the child cries without tears.

Pupillary reflex is present in the newborn, but

in its appearance it becomes "adult" only to 3-6

years.

Age features of the visual analyzer

By 4 months – formation of the central visual

fossa (fovea centralis) and myelination of the

visual pathways is completed

By 1 year – there is an intensive development

of neurons of the lateral geniculate body and

visual projection zones of the cortex

Up to 6-7 years – the formation of multiple

connections between the neurons of the

associative zones of the cortex involved in the

analysis of visual information occurs.

Age features of the visual analyzer

89% of newborns have hypermetropia, and only 11% have emmetropia.

Hyperopia is caused by the spherical shape of the eye and its short

anteroposterior axis. Due to the growth of the eyeball, hypermetropia

gradually decreases.

By the age of 8-12, the eye becomes emmetropic. At the same time,

primarily because of the location of the text, which is too close (less than 30

cm from the eye), in 30-40% of children the anteroposterior size of the

eyeball increases with age, which leads to myopia (nearsighted) – one of the

most common anomalies of eye refraction .

Visual acuity

Age features of the visual analyzer

Myopia – nearsightedness – light focuses

in front of the retina. This may depend on

the large refractive power of the eye or the

large length of the eyeball. To correct

vision use glasses with scattering lenses.

With congenital farsightedness, the eyeball

is shortened and the distant objects person

can see normally, but when viewing close

subjects, the focal length is retracted

behind the retina.

Visual acuity is related to the structure of

the visual analyzer

Visual acuity – the ability to distinguish small details of the subject, in

newborns is very low – in the range of 0.004-0.002 c. units, in 1 year

it is 0.3-0.6; in 3 years - 0,6-1,0; in 5 years - 0,8-1,0; in 7 years and

older - 0,9-1,0.

Normal visual acuity is established in 3-5 years. The growth of visual

acuity is associated with morphological development of the retina

(shift of bipolar and amacrine cells away from the central fossa).

Age features of the visual analyzer

In children, the lens has a high elasticity,

which contributes to the high accommodation

capacity of the eye.

Accommodation maximum development –

at 10-year-old age. During this period the

accommodation volume is 14 D, at 15 years – 12

D, at 20 years – 10 D, at 30 years – 7 D.

The nearest point of clear vision

(characterizes accommodative capacity):

10 years – 10 cm;

in 20 years – 8.3 cm;

in 30 years – 11 cm;

in 40 years – 17 cm;

in 60 years - 80 cm.

REDUCING THE EYE'S ACCOMODATION ABILITY

REFLECTS THE AGING PROCESS AND IS

ASSOCIATED WITH MANY CAUSES, INCLUDING A

DECREASE IN THE ELASTICITY OF THE LENS AND

LIGAMENT OF ZINN.

Age features of the visual analyzer

Binocular vision – provides a relief

perception of the surrounding world, the

depth of the location of objects and the

distance on which they are located.

Develops gradually.

From the 3-week-old age, the child

stably binocularly fixes eyes on fixed

objects.

After 6-9 months there is a

stereoscopic perception and sense of

depth, which reaches perfection by 16-

17 years.

After 40 years – this ability is reduced.

Age features of the visual analyzer

In newborn number of cones is less than rods.

Up to 4 months, despite the functioning of the rods, the field of vision is very

narrow. Gradually, there is an expansion of peripheral vision, especially in the

period from 5 to 10 years.

By 6 months the central part of the retina is fully developed. At birth, the

child does not differentiate colors due to the immaturity of the cones. The

differentiation of colors begins at 5-6 months (conditioned reflexes

development), but a conscious sense of colors is formed later.

Children can name colors of the painted subjects already in 2,5-3 years. At 3

years the child differentiates the absolute value of the brightness and the

ratio of the brightness of the colors.

A significant increase in the ability to differentiate colors is observed in 10-12

years (maximum – in 30 years, then this ability decreases). In general, with

age, absolute sensitivity to colors decreases, and the ability to distinguish

color shades, on the contrary, increases.

Age features of the visual analyzer

Light sensitivity in newborns is

low. Since the first months of life, it

has multiplied, reaching its maximum

development by 20 years.

After 30 years, it begins to

decline. Functional mobility of the

analyzer, determined, for example,

by the maximum fusion frequency of

light flashes, rises to 30 years.

Dark and light adaptation is

poorly developed in newborns and

infants. The ability to dark adaptation

increases to 20 years, and to light –

up to 24 years.

Age features of the visual analyzer

Age features of the visual analyzer

With age, often the lens loses its elasticity and becomes more

flat, the image of closely located objects goes behind the retina

– develops acquired farsightedness

Age-related changes of vision in elderly people

Vision impairment. The most common eye problems are

myopia (nearsightedness), astigmatism (distorted vision),

hyperopia (farsightedness) and presbyopia (trouble focusing on

close objects). Often corrected by glasses, contacts or

sometimes surgery.

Vision impairment

Age-related changes of vision in elderly people

Age-related macular degeneration (AMD) – damages sharp

and central vision. Treatment for wet AMD ranges from lasers to

injections. No singular proven treatment for dry AMD.

Vision with AMD

Age-related changes of vision in elderly people

Cataract – clouding of the eye’s

lens. Glasses and better lighting

can help but surgery is usually

required.

Vision with cataract

Age-related changes of vision in elderly people

Glaucoma. Damages the eye’s

optic nerve, resulting in vision loss

and blindness. Treated with eye

drops, pills, or surgery.

Vision with glaucoma

Age-related changes of vision in elderly people

Diabetic retinopathy (DR). This

complication of diabetes, the

leading cause of blindness in

adults, causes progressive damage

to the retina. Prevention is key.

Treatment ranges from injectable

medication to surgery.

Vision with DR

Thank you for your

attention!