These photoreceptors are cylindrical in shape, with a length of approximately 0.06 mm and a diameter of approximately 0.002 mm. Thus, such a cylinder is really quite similar to a stick. Eye healthy person contains approximately 115-120 million rods.
The human eye rod can be divided into 4 segmental zones:
1 - Outer segmental zone (includes membranous discs containing rhodopsin),
2 - Connecting segmental zone (cilium),
4 - Basal segmental zone (nerve connection).
Rods are highly photosensitive. So, for their reaction, the energy of 1 photon (the smallest, elementary particle Sveta). This fact very important for night vision, which allows you to see in low light.
Rods cannot distinguish colors; this is primarily due to the presence of only one pigment in them - rhodopsin. The pigment rhodopsin, otherwise called visual purple, due to the included protein groups (chromophores and opsins), has 2 light absorption maxima. True, one of the maxima exists beyond the range of light visible to the human eye (278 nm - the region of ultraviolet radiation), therefore, it is probably worth calling it the wave absorption maximum. But the second maximum is visible to the eye - it exists at around 498 nm, located on the border of the green and blue color spectrum.
It is reliably known that rhodopsin, present in rods, reacts to light much more slowly than iodopsin, contained in cones. Therefore, rods are characterized by a weak reaction to the dynamics of light fluxes, and in addition, they poorly distinguish the movements of objects. And visual acuity is not their prerogative.
Cones of the retina
These photoreceptors also got their name due to their characteristic shape, similar to the shape of laboratory flasks. The length of the cone is approximately 0.05 mm, its diameter at the narrowest point is approximately 0.001 mm, and at the widest point it is 0.004. The retina of a healthy adult contains about 7 million cones.
Cones have less sensitivity to light. That is, to excite their activity, a luminous flux will be required, which is tens of times more intense than to excite the work of rods. But cones process light fluxes much more intensely than rods, so they perceive their changes better (for example, they better distinguish light when objects move, in dynamics relative to the eye). They also define images more clearly.
The cones of the human eye also include 4 segmental zones:
1 - Outer segmental zone (includes membranous discs containing iodopsin),
2 - Connecting segmental zone (constriction),
3 - Internal segmental zone (includes mitochondria),
4 - Synaptic connection zone or basal segment.
The reason for the above-described properties of cones is the content of the specific pigment iodopsin in them. Today, 2 types of this pigment have been isolated and proven: erythrolab (iodopsin, sensitive to the red spectrum and long L-waves), and chlorolab (iodopsin, sensitive to the green spectrum and medium M-waves). A pigment that is sensitive to the blue spectrum and short S-waves has not yet been found, although the name has already been assigned to it - cyanolab.
The division of cones according to the type of dominance of color pigment in them (erythrolab, chlorolab, cyanolab) is due to the three-component vision hypothesis. There is, however, another theory of vision - nonlinear two-component. Its adherents believe that all cones contain erythrolab and chlorolab at the same time, and therefore are able to perceive colors in both the red and green spectrum. The role of cyanolabe, in this case, is played by the faded rhodopsin of the rods. This theory is also confirmed by examples of people suffering from color blindness, namely the inability to distinguish the blue part of the spectrum (tritanopia). They also have difficulty seeing at night (hemeralopia), which is a sign of abnormal rod activity in the retina.
Video about the structure of rods and cones
Symptoms of damage to the rods and cones of the retina
- Decreased visual acuity.
- Color vision impairment.
- "Lightning" before my eyes.
- Narrowing of the field of view.
- Veil before the eyes.
- Deterioration of twilight vision.
Diseases affecting rods and cones
Damage to the rods and cones of the eye is possible when various pathologies retina:
- Hemeralopia ("night blindness").
- Macular degeneration.
- Retinal pigment abiotrophy.
- Colorblindness.
- Retinal disinsertion.
- Inflammation of the retina (retinitis, chorioretinitis).
The light-sensitive part of the eye is a mosaic of light-sensitive cells (photoreceptors) located on the retina. The retina of the eye contains two types of light-sensitive receptors, occupying an area with an aperture of about 170° relative to the visual axis: 120...130 million rods (long and thin receptors for night vision), 6.5...7.0 million cones (short and thick receptors for daytime vision) . Before light reaches the retina, it must first pass through a layer of nerve tissue and a layer blood vessels. This arrangement of photosensitive elements from the point of view common sense is not optimal. Any television camera designer would have taken care to install the connecting wires so as not to interfere with the light falling on the photocells. The retina is constructed on a different principle and the reasons for this reverse retinal structure are not fully understood.
The rods and cones are tightly adjacent to each other with their elongated sides. Their dimensions are very small: the length of the rods is 0.06 mm, the diameter is 0.002 mm, the length and diameter of the cones are 0.035 and 0.006 mm, respectively. The density of rods and cones in different parts of the retina ranges from 20,000 to 200,000 per 1 mm 2. In this case, cones predominate in the center of the retina, rods - in the periphery. In the center of the retina there is the so-called oval-shaped macula macula (length 2 mm, width 0.8 mm). In this place there are almost only cones. The “macula” is the area of the retina that provides the clearest sharp vision.
Rods and cones differ in the light-sensitive substances they contain. The substance of the rods is rhodopsin (visual purple). The maximum light absorption of rhodopsin corresponds to a wavelength of approximately 510 nm (green light), i.e., rods have maximum sensitivity to radiation with λ = 510 nm . The light-sensitive substance of cones (iodopsin) comes in three types, each of which has maximum absorption in different zones of the spectrum.
Under the influence of light, the molecules of photosensitive substances dissociate (disintegrate) into positively and negatively charged particles. When the concentration of ions and, consequently, their total electrical charge reaches a certain value, under the influence of the charge, a current pulse appears in the nerve fiber, which is sent to the brain.
The reactions of light decay of rhodopsin and iodopsin are reversible, that is, after they were decomposed into ions under the influence of light and the charge of the ions excited a current pulse in the nerve, these substances are again restored to their original light-sensitive form. Energy for restoration is provided by products that enter the eye through an extensive network of tiny blood vessels. Thus, a continuous cycle of destruction and subsequent restoration of light-sensitive substances is established in the eye.
If the level of the amount of light acting on the eye does not change over time, then a mobile equilibrium is established between the concentrations of substances in states of decay and the original photosensitive form. The magnitude of this concentration depends on the amount of light acting on the eye at a given or previous moment, i.e. The light sensitivity of the eye changes at different levels of active light.
It is known that if you enter a very dimly lit room from a bright light, at first the eye does not distinguish anything. Gradually, the eye's ability to distinguish objects is restored. After a long stay in the dark (about 1 hour), the sensitivity of the eye becomes maximum, as the concentration of photosensitive substances reaches its upper limit. If, after a long stay in the dark, you come out into the light, then at the first moment the eye will be in a state of blindness: the restoration of photosensitive substances lags behind their decay. Gradually the eye adapts to the level of illumination and begins to work normally.
Let us recall that the property of the eye to adapt to the level of the amount of active light, which is expressed by a change in its light sensitivity, is called adaptation.
Rods – night vision. Rods can react to the smallest amount of light. They are responsible for our ability to see in the moonlight, the light of the starry sky, and even in cases where the starry sky is hidden by clouds. In Fig. 2.2 the dotted curve displays the dependence of the sensitivity of the rods on the wavelength. Rods provide only achromatic, or color-neutral perception in the form of white, gray and black. Moreover, each rod does not have a direct connection with the brain. They unite in groups. Such a device explains the high sensitivity of rod vision, but prevents it from distinguishing the smallest details. These facts explain the general colorlessness and blurriness of night vision and the truth of the proverb: “At night, all cats are
 |
ry."
Rice. 2.2. Relative spectral sensitivity of rods and cones
Cones – daytime vision. The response of cones is more complex than that of rods. Instead of simply distinguishing between light and dark, and perceiving a range of different gray colors, cones provide the perception of chromatic colors. In other words, with cone vision we can see various colors. The spectral distribution of cone vision sensitivity by wavelength is shown in Fig. 2.2 with a solid line. This curve is usually called the visibility curve, as well as the spectral sensitivity curve of the eye. Rod vision, compared to cone vision, is much more sensitive to radiation in the short-wavelength portion of the visible spectrum, and sensitivity to radiation in the long-wavelength (red) portion of the spectrum is approximately the same as that of cones. However, the cones continue to respond to small increases in the intensity of the incident light (forming an image on the retina) even when the density of its flux for some time becomes so great that the rods no longer respond to them - they are saturated. In other words, all rods in this case give the maximum possible number of nerve signals. Thus, our daytime vision is provided almost entirely by cones. The shift in sensitivity to light along the wavelength axis from cone (daytime) vision to rod (or night) vision is called the Purkinje effect (more correctly Purkinje). This “Purkinje shift,” named after the Czech scientist Purkinje who first discovered it in 1823, is responsible for the fact that an object that is red in daylight is perceived as black in night or twilight lighting, while an object that is perceived Like blue during the day, appears light gray at night.
Having two types of light-sensitive receptors (rods and cones) in humans is a great advantage. Not all animals are so lucky. Chickens, for example, only have cones and therefore must go to bed when the sun goes down. Owls only have sticks; they have to squint their eyes all day.
Rods and cones - twilight vision. Both rods and cones are involved in twilight vision. Twilight is the range of illumination that extends from the illumination created by the radiation from the sky when the sun has dropped more than a few degrees below the horizon, to the illumination provided by the moon rising high in a clear sky at half-phase. Twilight vision also includes vision in a dimly lit room (for example, with candles). Because under such conditions the relative contribution of rod and cone vision to overall visual perception is constantly changing, color judgments are extremely unreliable. However, there are a number of products whose color assessment must be done using such mixed vision, since they are intended for us to consume in dim light. An example is phosphorescent paint used in road signs for dark conditions.
Brain work
Information from the receptors is transmitted to the brain via the optic nerve, which contains about 800 thousand fibers. In addition to this direct transmission of excitation from the retina to the brain centers, there is complex feedback to control, for example, the movements of the eyeballs.
Somewhere in the retina, complex information processing occurs - the logarithm of current density and the conversion of the logarithm into pulse frequency. Next, information about brightness, encoded by the pulse frequency, is transmitted along the optic nerve fiber to the brain. However, it is not just current that passes through the nerve, but a complex process of excitation, some combination of electrical and chemical phenomena. In contrast of electric current is emphasized by the fact that the speed of signal propagation along the nerve is very low. It lies in the range from 20 to 70 m/s.
Information coming from the three types of cones is converted into impulses and encoded in the retina before being transmitted to the brain. This encoded information is sent as a luminance signal from all three types of cones, as well as difference signals for each two colors (Figure 2.3). A second brightness channel is also connected here, probably originating from an independent wand system.
The first difference color signal is K-Z signal. It is formed by red and green cones. The second signal is signal J-S, which is obtained in a similar way, except that the information about the yellow color is obtained by adding the input sig
 |
catches from K+Z cones.
Fig.2.3. Model visual system
The brain has more than once been likened to a giant center that collects and processes a large amount of information. Attempts to understand the millions of connections in this incredibly complex device have been largely successful. We know, for example, that optic nerve one eye connects to the optic nerve of the other (optic chiasm) in such a way that the nerve fibers of the right half of one retina run next to the fibers from the right half of the other retina and, after passing through the relay station (geniculate body) in the midbrain, end their path in almost the same in the same place in the occipital lobe of the brain, in the back of it. The excitations of the retina are projected in this lobe, and the part of them corresponding to the center of the eye (the macula) is greatly enhanced compared to the excitations of other parts of the retina. The relay station has the ability for lateral connections, and itself occipital part has many connections with all other parts of the brain.
38. Photoreceptors (rods and cones), differences between them. Biophysical processes occurring during the absorption of a light quantum in photoreceptors. Visual pigments of rods and cones. Photoisomerization of rhodopsin. Mechanism of color vision.
.3. BIOPHYSICS OF LIGHT PERCEPTION IN THE RETINA Structure of the retina
The structure of the eye that produces the image is called retina(retina). In it, in the outermost layer, there are photoreceptor cells - rods and cones. The next layer is formed by bipolar neurons, and the third layer is formed by ganglion cells (Fig. 4). Between the rods (cones) and the dendrites of the bipolars, as well as between the axons of the bipolars and ganglion cells there are synapses. The axons of ganglion cells form optic nerve. Outside the retina (counting from the center of the eye) lies a black layer of pigment epithelium, which absorbs unused radiation (not absorbed by photoreceptors) passing through the retina 5*). On the other side of the retina (closer to the center) is choroid, supplying oxygen and nutrients to the retina.
Rods and cones consist of two parts (segments) . Internal segment is an ordinary cell with a nucleus, mitochondria (there are a lot of them in photoreceptors) and other structures. Outer segment. almost entirely filled with disks formed by phospholipid membranes (up to 1000 disks in rods, about 300 in cones). The membranes of the discs contain approximately 50% phospholipids and 50% of a special visual pigment, which in rods is called rhodopsin(in its pink color; rhodos is pink in Greek), and in cones iodopsin. Below, for brevity, we will only talk about sticks; the processes in cones are similar. The differences between cones and rods will be discussed in another section. Rhodopsin is made up of protein opsin, to which is attached a group called retinal. . Retinal in its chemical structure is very close to vitamin A, from which it is synthesized in the body. Therefore, a lack of vitamin A can cause vision impairment.
Differences between rods and cones
1. Difference in Sensitivity. . The threshold for sensing light in rods is much lower than in cones. This, firstly, is explained by the fact that there are more disks in rods than in cones and, therefore, there is a greater likelihood of absorbing light quanta. However, main reason in a different. Neighboring rods via electrical synapses. are combined into complexes called receptive fields .. Electrical synapses ( connexons) can open and close; therefore, the number of rods in the receptive field can vary widely depending on the level of illumination: the weaker the light, the larger the receptive fields. In very low light conditions, over a thousand rods can unite in a field. The point of this combination is that it increases the useful signal to noise ratio. As a result of thermal fluctuations, a chaotically changing potential difference appears on the membranes of the rods, which is called noise. In low light conditions, the amplitude of the noise can exceed the useful signal, that is, the amount of hyperpolarization caused by the action of light. It may seem that under such conditions the reception of light will become impossible. However, in the case of perception of light not by a separate rod, but by a large receptive field, there is a fundamental difference between noise and a useful signal. The useful signal in this case arises as the sum of the signals created by the rods united into a single system - receptive field . These signals are coherent, they come from all the rods in the same phase. Due to the chaotic nature of thermal motion, noise signals are incoherent; they arrive in random phases. From the theory of addition of oscillations it is known that for coherent signals the total amplitude is equal to : Asumm = A 1 n, Where A 1 - amplitude of a single signal, n- number of signals. In the case of incoherent ones. signals (noise) Asumm=A 1 5.7n. Let, for example, the amplitude of the useful signal be 10 μV, and the amplitude of the noise 50 μV. It is clear that the signal will be lost against the background noise. If 1000 rods are combined into a receptive field, the total useful signal will be 10 μV
10 mV, and the total noise is 50 μV 5. 7 = 1650 μV = 1.65 mV, that is, the signal will be 6 times more noise. With this attitude, the signal will be confidently perceived and create a feeling of light. Cones work in good illumination, when even in a single cone the signal (PRP) is much greater than the noise. Therefore, each cone usually sends its signal to the bipolar and ganglion cells independently of the others. However, if illumination decreases, cones can also combine into receptive fields. True, the number of cones in a field is usually small (several dozen). In general, cones provide daytime vision, rods provide twilight vision.
2.Difference in Resolution.. The resolution of the eye is characterized by the minimum angle at which two adjacent points of an object are still visible separately. Resolution is mainly determined by the distance between adjacent photoreceptor cells. To prevent two points from merging into one, their image must fall on two cones, between which there will be another one (see Fig. 5). On average, this corresponds to a minimum visual angle of about one minute, that is, the resolution of cone vision is high. Rods are usually combined into receptive fields. All points whose images fall on one receptive field will be perceived
swear like one point, since the entire receptive field sends a single total signal to the central nervous system. That's why resolution (visual acuity) with rod (twilight) vision it is low. When there is insufficient illumination, the rods also begin to unite into receptive fields, and visual acuity decreases. Therefore, when determining visual acuity, the table must be well illuminated, otherwise a significant mistake can be made.
3. Difference in placement. When we want to get a better look at an object, we turn so that this object is in the center of the field of view. Since cones provide high resolution, cones predominate in the center of the retina - this contributes to good visual acuity. Since the color of the cones is yellow, this area of the retina is called the macula macula. On the periphery, on the contrary, there are many more rods (although there are also cones). There, visual acuity is noticeably worse than in the center of the visual field. In general, there are 25 times more rods than cones.
4. Difference in color perception.Color vision is inherent only to cones; the image produced by the sticks is monochromatic.
Color vision mechanism
In order for a visual sensation to arise, it is necessary that light quanta be absorbed in photoreceptor cells, or more precisely, in rhodopsin and iodopsin. Light absorption depends on the wavelength of light; Each substance has a specific absorption spectrum. Research has shown that there are three types of iodopsin with different absorption spectra. U
of one type, the absorption maximum lies in the blue part of the spectrum, another - in green and a third - in red (Fig. 5). Each cone contains a single pigment, and the signal sent by that cone corresponds to the absorption of light by that pigment. Cones containing a different pigment will send different signals. Depending on the spectrum of light incident on a given area of the retina, the ratio of signals coming from the cones different types, turns out to be different, but in general the totality of signals received by the visual center of the central nervous system will characterize the spectral composition of the perceived light, which gives subjective feeling of color.
The visual organ is a complex mechanism optical vision. It contains eyeball, the optic nerve with its auxiliary nervous tissues - the lacrimal system, eyelids, muscles of the eyeball, as well as the lens and retina. The visual process begins with the retina.
The retina has two different functional parts: the visual or optical part; the part is blind or ciliated. The retina has the inner covering layer of the eye, which is separate part located on the periphery of the visual system.
It consists of receptors of photographic significance - cones and rods, which perform the initial processing of incoming light signals, in the form electromagnetic radiation. This organ lies in a thin layer, inside next to vitreous, and the outer side is adjacent to vascular system surface of the eyeball.
The retina is divided into two parts: a larger part responsible for vision and a smaller part – the blind part. The diameter of the retina is 22 mm and it occupies about 72% of the surface of the eyeball.
Rods and cones play a huge role in light and color perception
In the eye organ, the retina, the existing photoreceptors play an important role in the color perception of images. These are receptors - cones and rods, located unevenly. Their density ranges from 20 to 200 thousand per square millimeter.
In the center of the retina is a large number of cones, with more rods located around the periphery. There is also the so-called yellow spot, where there are no sticks at all.
They allow you to see all the shades and brightness of surrounding objects. The high sensitivity of this type of receptor makes it possible to capture light signals and convert them into impulses, which are then sent along the visual nerve channels to the brain.
During daylight hours, the receptors - the cones of the eye - work; at dusk and at night, human vision is provided by the receptors - the rods. If a person sees a color picture during the day, then at night only black and white. Each of the receptors of the photographic system obeys a strictly assigned function.
Structure of rods
Rods and cones are similar in structure Cones and rods are similar in structure, but they differ due to the different functional jobs they perform and the perception of light flux. Rods are one of the receptors, named for their cylindrical shape. Their number in this part is about 120 million.
They are quite short, 0.06 mm long and 0.002 mm wide. Receptors have four constituent fragments:
- outer section - discs in the form of a membrane;
- intermediate sector - eyelash;
- inner part - mitochondria;
- tissue with nerve endings.
The photocell is capable of responding to weak flashes of light of one photon, thanks to its high sensitivity. It contains one component called rhodopsin or visual purple.
Rhodopsin degrades in bright light and becomes sensitive to blue vision. In the dark or twilight, rhodopsin is restored after half an hour, and the eye is able to see objects.
Rhodopsin gets its name from its bright red color. In the world he acquires yellow, then becomes discolored. In the dark it turns bright red again.
This receptor is not able to recognize color and shades, but allows you to see in evening time outlines of objects. It reacts to light much more slowly than cone receptors.
Cone structure
Cones are less sensitive than rods The cones are conical in shape. Number of cones in this department 6–7 million, length up to 50 microns, and thickness up to 4 mm. It contains the component iodopsin. The component additionally consists of pigments:
- chlorolab - a pigment that can react to yellow - green colors;
- erythrolab is an element capable of sensing yellow-red colors.
There is also a third, separately presented pigment: cyanolab - a component that perceives the violet-blue part of the spectrum.
Cones are 100 times less sensitive than rods, but the perceptual response to movement is much faster. The cone receptor consists of 4 component fragments:
- outer part – membrane disks;
- intermediate link - constriction;
- inner segment – mitochondria;
- synaptic area.
The part of the discs in the outer part facing the light flux is constantly renewed, restoration and replacement of visual pigment is underway. More than 80 disks are replaced within 24 hours; a complete replacement of disks is carried out in 10 days. The cones themselves differ in wavelength; there are three types:
- S – type reacts to the violet-blue part;
- M – type perceives the green-yellow part;
- L – type distinguishes between yellow and red parts.
Rods are a photoreceptor that senses light, and cones are a photoreceptor that senses color. These types of cones and rods together create the possibility of color perception of the surrounding world.
Rods and cones of the retina: diseases
Receptor groups that provide full color perception of objects are very sensitive and can be susceptible to various diseases.
Diseases and symptoms
Known disease- color blindness - disruption of the functioning of the rods and cones Diseases affecting retinal photoreceptors:
- Colorblindness is the inability to recognize colors;
- Retinal pigmentary degeneration;
- Chorioretinitis - inflammation of the retina and membrane vessels;
- Departure of the layers of the retinal membrane;
- Night blindness or hemeralopia, this is a visual impairment at dusk, occurs with pathology of the rods;
Macular degeneration is a nutritional disorder in the central part of the retina. The following symptoms are observed with this disease:
- fog before the eyes;
- difficult to read, recognize faces;
- straight lines are distorted.
Other diseases have pronounced symptoms:
- The indicator of vision decreases;
- Impaired color perception;
- Flashes of light in the eyes;
- Narrowing viewing radius;
- Presence of a veil before the eyes;
- Deterioration of vision at dusk.
Rods and cones are a real paradox! Night blindness or hemeralopia occurs due to a lack of vitamin A, and then the function of the rods is disrupted, when a person cannot see at all in the evening and in the dark, but sees perfectly during the day.
A functional disorder of the cones leads to photophobia, where vision is normal in low light and blindness occurs in bright light. Color blindness – achromasia – may develop.
Everyday care of your vision, protection from harmful effects, prevention of maintaining visual acuity, harmonious and color perception is a priority task for those who want to preserve the organ of vision - the eyes, have vigilance in their gaze and the versatility of a full life without disease.
An educational video will tell you about the paradoxes of vision:
The rods and cones of the retina are peculiar photoreceptors of the visual organs. The responsibility of the cones is to transform the energy received from light into special parts of the brain, as a result of which human eye able to visually perceive his environment. Rods are responsible for the ability to navigate in the dark or so-called twilight vision. Rods perceive only dark and light tones. In contrast, cones perceive millions of colors and their shades, and are also responsible for visual acuity. Each of these receptors has a special structure, thanks to which it performs its functions.
Rods and cones are sensitive receptors in the retina of the eye that transform light stimulation into nervous stimulation.
The sticks got their name from their cylindrical shape. Each stick is divided into four main parts:
- basal part, responsible for connecting nerve cells;
- the connecting part provides connection with the eyelashes;
- outer part;
- the inner part contains mitochondria that produce energy.
In order to excite the photoreceptor, the energy of one photon is sufficient. This energy is enough for the eyes to be able to distinguish objects in the dark. Receiving light energy, the retinal rods become irritated, and the pigment they contain begins to absorb light waves.
Cones got their name due to their similarity to a regular medical flask. They are also divided into four parts. The cones contain another pigment that is responsible for distinguishing green and red shades. Interesting fact is that the pigment that recognizes shades of blue color, modern medicine not installed.
Rods are responsible for perception in low light conditions, cones are responsible for visual acuity and color perception The role of photoreceptors in the structure of the eyeball
The interconnected work of cones and rods is called photoreception, that is, the change in the received energy from light waves into specific visual images. If this interaction is disrupted in the eyeball, then the person loses a significant part of his vision. For example, a malfunction of the rods can lead to a person losing the ability to navigate in darkness and twilight.
The cones of the retina perceive light waves coming in during daylight conditions. Also, thanks to them, the human eye has “clear” color vision.
Symptoms of photoreceptor dysfunction
Diseases accompanied by pathologies in the photoreceptor area have the following symptoms:
- deterioration in the “quality” of vision.
- various lighting effects before the eyes (glare, flashes, veil).
- blurred vision at dusk;
- problems associated with color differences;
- reduction in the size of visual fields.
Most of the diseases associated with the organs of vision have characteristic symptoms, by which it is quite easy for a specialist to identify the disease. Such diseases may include color blindness and hemeralopia. However, there are a number of diseases that are accompanied by the same symptoms, and it is possible to identify a specific pathology only with in-depth diagnostics and prolonged collection of anamnesis data.
Cones get their name due to their shape, similar to laboratory flasks. Diagnostic technique
To diagnose pathologies associated with the work of cones and rods, a whole range of examinations is prescribed:
- study of the width of visual fields;
- study of the condition of the fundus of the visual organs;
- comprehensive test for the perception of colors and their shades;
- UV and ultrasound of the eyeball;
- FA - an examination that allows you to visualize the state of the vascular system;
- refractometry.
Correct color perception and visual acuity directly depend on the functioning of rods and cones. It is impossible to answer the question of how many cones there are in the retina, since their number is in the millions. At various diseases the retina of the visual organ disrupts the functioning of these receptors, which can lead to partial or complete loss of vision.
Photoreceptor diseases
Today, the following diseases affecting the photoreceptors of the visual organs are known:
- detachment of the retina of the eyeball;
- age-related retinal degeneration;
- retinal macular degeneration;
- color blindness;
- chorioretinitis.
The adult retina contains about 7 million cones. Prevention of eye diseases
Long-term eye strain is the main cause of fatigue and tension in the visual organs. Constant load can lead to serious consequences and cause the development serious illnesses which may result in vision loss.
Experts say that by following a certain technique, you can successfully combat eye fatigue and prevent the occurrence of pathological changes. The main factor in this matter is proper lighting. Ophthalmologists do not recommend reading or working at a computer in a room with dim light. Lack of lighting can cause severe tension in the eyeballs.
If you use optical lenses and glasses, the diopter size should be selected by a specialist. To do this, you can undergo special tests in the ophthalmologist's office that will reveal visual acuity.
Constant work at the computer leads to the fact that the eyeball begins to lose moisture. This is why it is important to take small intervals so that your eyes can rest. The ideal solution for visual health would be five-minute breaks every one hour. Once every three or four hours it is necessary to perform gymnastic exercises for the eyes.
Another important factor in the prevention of diseases of the organs of vision is proper diet. The food consumed should contain vitamins and useful material. It is recommended to eat more fresh vegetables, fruits and berries, as well as dairy products.
In contact with
