Anatomy of the Eye | Kellogg Eye Center

• Choroid
  Layer containing blood vessels that lines the back of the eye and is located between the retina (the inner light-sensitive layer) and the sclera (the outer white eye wall).  
• Ciliary Body
  Structure containing muscle and is located behind the iris, which focuses the lens.
• Cornea
  The clear front window of the eye which transmits and focuses (i.e., sharpness or clarity) light into the eye. Corrective laser surgery reshapes the cornea, changing the focus.
• Fovea
  The center of the macula which provides the sharp vision.
• Iris
  The colored part of the eye which helps regulate the amount of light entering the eye. When there is bright light, the iris closes the pupil to let in less light. And when there is low light, the iris opens up the pupil to let in more light.
• Lens
  Focuses light rays onto the retina. The lens is transparent, and can be replaced if necessary. Our lens deteriorates as we age, resulting in the need for reading glasses. Intraocular lenses are used to replace lenses clouded by cataracts.
• Macula
  The area in the retina that contains special light-sensitive cells. In the macula these light-sensitive cells allow us to see fine details clearly in the center of our visual field. The deterioration of the macula is a common condition as we get older (age related macular degeneration or ARMD).
• Optic Nerve
  A bundle of more than a million nerve fibers carrying visual messages from the retina to the brain. (In order to see, we must have light and our eyes must be connected to the brain.) Your brain actually controls what you see, since it combines images. The retina sees images upside down but the brain turns images right side up. This reversal of the images that we see is much like a mirror in a camera. Glaucoma is one of the most common eye conditions related to optic nerve damage.
• Pupil
  The dark center opening in the middle of the iris. The pupil changes size to adjust for the amount of light available (smaller for bright light and larger for low light). This opening and closing of light into the eye is much like the aperture in most 35 mm cameras which lets in more or less light depending upon the conditions.
• Retina
  The nerve layer lining the back of the eye. The retina senses light and creates electrical impulses that are sent through the optic nerve to the brain.
• Sclera
  The white outer coat of the eye, surrounding the iris.
• Vitreous Humor
  The, clear, gelatinous substance filling the central cavity of the eye.

The five senses include sight, sound, taste, hearing and touch. Sight, like the other senses is closely related to other parts of our anatomy. The eye is connected to the brain and dependent upon the brain to interpret what we see.

How we see depends upon the transfer of light. Light passes through the front of the eye (cornea) to the lens. The cornea and the lens help to focus the light rays onto the back of the eye (retina). The cells in the retina absorb and convert the light to electrochemical impulses which are transferred along the optic nerve and then to the brain.

The eye works much the same as a camera. The shutter of a camera can close or open depending upon the amount of light needed to expose the film in the back of the camera. The eye, like the camera shutter, operates in the same way. The iris and the pupil control how much light to let into the back of the eye. When it is very dark, our pupils are very large, letting in more light. The lens of a camera is able to focus on objects far away and up close with the help of mirrors and other mechanical devices. The lens of the eye helps us to focus but sometimes needs some additional help in order to focus clearly. Glasses, contact lenses, and artificial lenses all help us to see more clearly.  

8.5: The Eye – Biology LibreTexts

1. Last updated

2. Save as PDF

Page ID

40617

Vision is the special sense of sight that is based on the transduction of light stimuli received through the eyes. The eyes are located within either orbit in the skull. The bony orbits surround the eyeballs, protecting them and anchoring the soft tissues of the eye (Figure 8.13). The eyelids, with lashes at their leading edges, help to protect the eye from abrasions by blocking particles that may land on the surface of the eye. The inner surface of each lid is a thin membrane known as the palpebral conjunctiva. The conjunctiva extends over the white areas of the eye (the sclera), connecting the eyelids to the eyeball. Tears are produced by the lacrimal gland, located beneath the lateral edges of the nose. Tears produced by this gland flow through the lacrimal duct to the medial corner of the eye, where the tears flow over the conjunctiva, washing away foreign particles.

Figure 8.13. The Eye in the Orbit

The eye is located within the orbit and surrounded by soft tissues that protect and support its function. The orbit is surrounded by cranial bones of the skull.

Movement of the eye within the orbit is accomplished by the contraction of six extraocular muscles that originate from the bones of the orbit and insert into the surface of the eyeball (Figure 8.14). Four of the muscles are arranged at the cardinal points around the eye and are named for those locations. They are the superior rectus, medial rectus, inferior rectus, and lateral rectus. When each of these muscles contract, the eye to moves toward the contracting muscle. For example, when the superior rectus contracts, the eye rotates to look up. The superior oblique originates at the posterior orbit, near the origin of the four rectus muscles. However, the tendon of the oblique muscles threads through a pulley-like piece of cartilage known as the trochlea. The tendon inserts obliquely into the superior surface of the eye. The angle of the tendon through the trochlea means that contraction of the superior oblique rotates the eye medially. The inferior oblique muscle originates from the floor of the orbit and inserts into the inferolateral surface of the eye. When it contracts, it laterally rotates the eye, in opposition to the superior oblique. Rotation of the eye by the two oblique muscles is necessary because the eye is not perfectly aligned on the sagittal plane. When the eye looks up or down, the eye must also rotate slightly to compensate for the superior rectus pulling at approximately a 20-degree angle, rather than straight up. The same is true for the inferior rectus, which is compensated by contraction of the inferior oblique. A seventh muscle in the orbit is the levator palpebrae superioris, which is responsible for elevating and retracting the upper eyelid, a movement that usually occurs in concert with elevation of the eye by the superior rectus (see Figure 8.13). The extraocular muscles are innervated by three cranial nerves. The lateral rectus, which causes abduction of the eye, is innervated by the abducens nerve. The superior oblique is innervated by the trochlear nerve. All of the other muscles are innervated by the oculomotor nerve, as is the levator palpebrae superioris. The motor nuclei of these cranial nerves connect to the brain stem, which coordinates eye movements.

Figure 8.14. Extraocular Muscles

The extraocular muscles move the eye within the orbit.

The eye itself is a hollow sphere composed of three layers of tissue. The outermost layer is the fibrous tunic, which includes the white sclera and clear cornea. The sclera accounts for five sixths of the surface of the eye, most of which is not visible, though humans are unique compared with many other species in having so much of the “white of the eye” visible (Figure 8.15). The transparent cornea covers the anterior tip of the eye and allows light to enter the eye. The middle layer of the eye is the vascular tunic, which is mostly composed of the choroid, ciliary body, and iris. The choroid is a layer of highly vascularized connective tissue that provides a blood supply to the eyeball. The choroid is posterior to the ciliary body, a muscular structure that is attached to the lens by zonule fibers. These two structures bend the lens, allowing it to focus light on the back of the eye. Overlaying the ciliary body, and visible in the anterior eye, is the iris—the colored part of the eye. The iris is a smooth muscle that opens or closes the pupil, which is the hole at the center of the eye that allows light to enter. The iris constricts the pupil in response to bright light and dilates the pupil in response to dim light. The innermost layer of the eye is the neural tunic, or retina, which contains the nervous tissue responsible for photoreception. The eye is also divided into two cavities: the anterior cavity and the posterior cavity. The anterior cavity is the space between the cornea and lens, including the iris and ciliary body. It is filled with a watery fluid called the aqueous humor. The posterior cavity is the space behind the lens that extends to the posterior side of the interior eyeball, where the retina is located. The posterior cavity is filled with a more viscous fluid called the vitreous humor. The retina is composed of several layers and contains specialized cells for the initial processing of visual stimuli. The photoreceptors (rods and cones) change their membrane potential when stimulated by light energy. The change in membrane potential alters the amount of neurotransmitter that the photoreceptor cells release onto bipolar cells in the outer synaptic layer. It is the bipolar cell in the retina that connects a photoreceptor to a retinal ganglion cell (RGC) in the inner synaptic layer. There, amacrine cells additionally contribute to retinal processing before an action potential is produced by the RGC. The axons of RGCs, which lie at the innermost layer of the retina, collect at the optic disc and leave the eye as the optic nerve (see Figure 8. 15). Because these axons pass through the retina, there are no photoreceptors at the very back of the eye, where the optic nerve begins. This creates a “blind spot” in the retina, and a corresponding blind spot in our visual field.

Figure 8.15. Structure of the Eye

The sphere of the eye can be divided into anterior and posterior chambers. The wall of the eye is composed of three layers: the fibrous tunic, vascular tunic, and neural tunic. Within the neural tunic is the retina, with three layers of cells and two synaptic layers in between. The center of the retina has a small indentation known as the fovea.

Note that the photoreceptors in the retina (rods and cones) are located behind the axons, RGCs, bipolar cells, and retinal blood vessels. A significant amount of light is absorbed by these structures before the light reaches the photoreceptor cells. However, at the exact center of the retina is a small area known as the fovea. At the fovea, the retina lacks the supporting cells and blood vessels, and only contains photoreceptors. Therefore, visual acuity, or the sharpness of vision, is greatest at the fovea. This is because the fovea is where the least amount of incoming light is absorbed by other retinal structures (see Figure 8.15). As one moves in either direction from this central point of the retina, visual acuity drops significantly. In addition, each photoreceptor cell of the fovea is connected to a single RGC. Therefore, this RGC does not have to integrate inputs from multiple photoreceptors, which reduces the accuracy of visual transduction. Toward the edges of the retina, several photoreceptors converge on RGCs (through the bipolar cells) up to a ratio of 50 to 1. The difference in visual acuity between the fovea and peripheral retina is easily evidenced by looking directly at a word in the middle of this paragraph. The visual stimulus in the middle of the field of view falls on the fovea and is in the sharpest focus. Without moving your eyes off that word, notice that words at the beginning or end of the paragraph are not in focus. The images in your peripheral vision are focused by the peripheral retina, and have vague, blurry edges and words that are not as clearly identified. As a result, a large part of the neural function of the eyes is concerned with moving the eyes and head so that important visual stimuli are centered on the fovea. Light falling on the retina causes chemical changes to pigment molecules in the photoreceptors, ultimately leading to a change in the activity of the RGCs. Photoreceptor cells have two parts, the inner segment and the outer segment (Figure 8.16). The inner segment contains the nucleus and other common organelles of a cell, whereas the outer segment is a specialized region in which photoreception takes place. There are two types of photoreceptors—rods and cones—which differ in the shape of their outer segment. The rod-shaped outer segments of the rod photoreceptor contain a stack of membrane-bound discs that contain the photosensitive pigment rhodopsin. The cone-shaped outer segments of the cone photoreceptor contain their photosensitive pigments in infoldings of the cell membrane. There are three cone photopigments, called opsins, which are each sensitive to a particular wavelength of light. The wavelength of visible light determines its color. The pigments in human eyes are specialized in perceiving three different primary colors: red, green, and blue.

Figure 8.16. Photoreceptor

(a) All photoreceptors have inner segments containing the nucleus and other important organelles and outer segments with membrane arrays containing the photosensitive opsin molecules. Rod outer segments are long columnar shapes with stacks of membrane-bound discs that contain the rhodopsin pigment. Cone outer segments are short, tapered shapes with folds of membrane in place of the discs in the rods. (b) Tissue of the retina shows a dense layer of nuclei of the rods and cones. LM × 800. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

At the molecular level, visual stimuli cause changes in the photopigment molecule that lead to changes in membrane potential of the photoreceptor cell. A single unit of light is called a photon, which is described in physics as a packet of energy with properties of both a particle and a wave. The energy of a photon is represented by its wavelength, with each wavelength of visible light corresponding to a particular color. Visible light is electromagnetic radiation with a wavelength between 380 and 720 nm. Longer wavelengths of less than 380 nm fall into the infrared range, whereas shorter wavelengths of more than 720 nm fall into the ultraviolet range. Light with a wavelength of 380 nm is blue whereas light with a wavelength of 720 nm is dark red. All other colors fall between red and blue at various points along the wavelength scale. Opsin pigments are actually transmembrane proteins that contain a cofactor known as retinal. Retinal is a hydrocarbon molecule related to vitamin A. When a photon hits retinal, the long hydrocarbon chain of the molecule is biochemically altered. Specifically, photons cause some of the double-bonded carbons within the chain to switch from a cis to a trans conformation. This process is called photoisomerization. Before interacting with a photon, retinal’s flexible double-bonded carbons are in the cis conformation. This molecule is referred to as 11-cis-retinal. A photon interacting with the molecule causes the flexible double-bonded carbons to change to the trans– conformation, forming all-trans-retinal, which has a straight hydrocarbon chain (Figure 8.17). The shape change of retinal in the photoreceptors initiates visual transduction in the retina. Activation of retinal and the opsin proteins result in activation of a G protein. The G protein changes the membrane potential of the photoreceptor cell, which then releases less neurotransmitter into the outer synaptic layer of the retina. Until the retinal molecule is changed back to the 11-cis-retinal shape, the opsin cannot respond to light energy, which is called bleaching. When a large group of photopigments is bleached, the retina will send information as if opposing visual information is being perceived. After a bright flash of light, afterimages are usually seen in negative. The photoisomerization is reversed by a series of enzymatic changes so that the retinal responds to more light energy.

Figure 8.17. Retinal Isomers

The retinal molecule has two isomers, (a) one before a photon interacts with it and (b) one that is altered through photoisomerization.

The opsins are sensitive to limited wavelengths of light. Rhodopsin, the photopigment in rods, is most sensitive to light at a wavelength of 498 nm. The three color opsins have peak sensitivities of 564 nm, 534 nm, and 420 nm corresponding roughly to the primary colors of red, green, and blue (Figure 8. 18). The absorbance of rhodopsin in the rods is much more sensitive than in the cone opsins; specifically, rods are sensitive to vision in low light conditions, and cones are sensitive to brighter conditions. In normal sunlight, rhodopsin will be constantly bleached while the cones are active. In a darkened room, there is not enough light to activate cone opsins, and vision is entirely dependent on rods. Rods are so sensitive to light that a single photon can result in an action potential from a rod’s corresponding RGC. The three types of cone opsins, being sensitive to different wavelengths of light, provide us with color vision. By comparing the activity of the three different cones, the brain can extract color information from visual stimuli. For example, a bright blue light that has a wavelength of approximately 450 nm would activate the “red” cones minimally, the “green” cones marginally, and the “blue” cones predominantly. The relative activation of the three different cones is calculated by the brain, which perceives the color as blue. However, cones cannot react to low-intensity light, and rods do not sense the color of light. Therefore, our low-light vision is—in essence—in grayscale. In other words, in a dark room, everything appears as a shade of gray. If you think that you can see colors in the dark, it is most likely because your brain knows what color something is and is relying on that memory.

Figure 8.18. Comparison of Color Sensitivity of Photopigments

Comparing the peak sensitivity and absorbance spectra of the four photopigments suggests that they are most sensitive to particular wavelengths.

Age Related Changes to the Eye

While not true for all people, the changes that occur to the eye as a part of aging generally result in some type of vision problem. These changes are known to include a slight shrinkage of the eye, an increase in the amount of connective tissue present, degeneration of some cells, and reduced blood supply.

The loss of fat and connective tissue surround the eye causes wrinkles in the corners of the eyes and sagging skin around the eye. As muscles around the eye weaken eyelids no longer fully close causing the cornea to become dry, irritated, and inflamed.

Age Related Dysfunctions of the Eye

Presbyopia, also known as farsightedness, is the result of the gradual loss of lens elasticity, a flattening of its shape, and an increase in its density. Presbyopia is so common it affects nearly everyone over the age of 40.

Blindness affects 16% of the population over the age of 75 in one or both eyes. While blindness is not a result of aging the incidence of blindness does increase with age.

Glaucoma is the result of elevated pressure within the eye. The pressure is causes by deficient drainage of fluid from the anterior cavity of the eye. The pressure can squeeze shut blood vessels within the eye causing degeneration of the optic nerve fibers and resulting in blindness.

Diabetic retinopathy is another cause of blindness in the aging population. This condition is a complication of diabetes. In some diabetics contractile cells in the wall of retinal capillaries swell and rupture, weakening the vessels and allowing them to dilate and form small pouches called microaneurysms. As blood travels through the larger damaged capillaries adjacent capillaries carry less blood depriving areas of the eye of blood flow. Blindness may result as the disease progresses.

Cataracts are cloudy lens that block from entering the eye. About 90% of people over the age of 70 are said to have some degree of cataract formation. The lenses are composed of fibers that are continuously growing. As the lenses thicken the fibers condense and interfere with the passage of light. The most effective treatment for cataracts is surgical removal.

Age related macular degeneration is a disease of the macular area of the retina. The disease results in the loss of central vision. While the exact causes of macular degeneration are currently unknown, it is thought that the disease disrupts the blood flow between the retina and subretina.

The retina is largely held in place by pressure. As one ages and the retina no longer tightly fits in place. When this happens the nervous-tissue layer can separate from the pigment layer resulting in a detached retina.

Contributors and Attributions

CC licensed content, Shared previously

• Chapter 14. Authored by: OpenStax College. Provided by: Rice University. Located at: openstaxcollege.org/files/textbook_version/low_res_pdf/13/col11496-lr.pdf. Project: Anatomy & Physiology. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/content/col11496/latest/.

---

8. 5: The Eye is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

1. Back to top

• Was this article helpful?

1. Article type

   Section or Page

   OER program or Publisher

   Lumen

2. Tags

   This page has no tags.

And an eye like an eagle

Olga Nesterenko,
Moscow Zoo
Chemistry and Life No. 6, 2017

It seems to us that animals see the world in much the same way as we do. In fact, their perception is very different from human. Even in birds – warm-blooded terrestrial vertebrates like us – the sense organs work differently than in humans.

Vision plays an important role in the life of birds. Anyone who can fly needs to navigate in flight, notice food in time, often at a great distance, or a predator (which, perhaps, can also fly and is approaching rapidly). So how is bird vision different from human vision?

To begin with, we note that the eyes of birds are very large. So, in an ostrich, their axial length is twice that of a human eye – 50 mm, almost like tennis balls! In herbivorous birds, the eyes make up 0.2-0.6% of the body weight, and in predatory, owls and other birds looking for prey from afar, the mass of the eyes can be two to three times the mass of the brain and reaches 3-4% of the body weight, in owls – up to 5%. For comparison: in an adult, the weight of the eyes is approximately 0.02% of the body weight, or 1% of the head weight. And, for example, in a starling, 15% of the mass of the head falls on the eyes, in owls – up to a third.

Visual acuity in birds is much higher than in humans – 4-5 times, in some species, probably up to 8. Carrion-eating vultures see the corpse of an ungulate animal 3-4 km away. Eagles notice prey from a distance of about 3 km, large species of falcons – from a distance of up to 1 km. And a kestrel falcon flying at a height of 10–40 m sees not only mice, but even insects in the grass.

What features of the structure of the eyes provide such visual acuity? One factor is size: large eyes produce large images on the retina. In addition, the bird’s retina has a high density of photoreceptors. People in the zone of maximum density have 150,000–240,000 photoreceptors per mm ² , in the house sparrow – 400,000, in the common buzzard – up to a million. In addition, good image resolution is determined by the ratio of the number of nerve ganglia to receptors. (If multiple receptors are connected to the same ganglion, resolution is reduced.) This ratio is much higher in birds than in humans. For example, in the white wagtail, there are about 100,000 ganglion cells per 120,000 photoreceptors.

Like mammals, birds have an area in their retina called the fovea, a depression in the middle of the macula. In the fovea, due to the high density of receptors, visual acuity is the highest. But it is interesting that 54% of bird species – raptors, kingfishers, hummingbirds, swallows, etc. – have another area with the highest visual acuity to improve lateral vision. It is more difficult for swifts to forage than for swallows, also because they have only one area of ​​sharp vision: swifts see well only forward, and their methods of catching insects on the fly are less diverse.

The eyes of most birds are fairly far apart. The field of view of each eye is 150–170°, but the overlap of the fields of both eyes (field of binocular vision) is only 20–30° in many birds. But a flying bird can see what is happening in front of it, from the sides, behind and even below (Fig. 1). For example, the large and protruding eyes of the American woodcock Scolopax minor are set high on a narrow head, and their field of view reaches 360° in the horizontal plane and 180° in the vertical plane. The woodcock has a field of binocular vision not only in front, but also behind! A very useful quality: a feeding woodcock sticks its beak into soft ground, looking for earthworms, insects, their larvae and other suitable food, while also seeing what is happening around. The large eyes of nightjars are slightly shifted back, their field of vision is also about 360 °. A wide field of view is characteristic of pigeons, ducks and many other birds.

In herons and bitterns, the field of binocular vision is shifted down, under the beak: it is narrow in the horizontal plane, but extended vertically, up to 170°. Such a bird, when holding its beak horizontally, can see its own paws with binocular vision. And even raising her beak up (as bitterns do when waiting for prey in reeds and disguising themselves due to vertical stripes on plumage), she is able to look down, notice small living creatures floating in the water and catch them with accurate throws. After all, binocular vision allows you to determine the distance to objects.

For many birds, it is more important not to have a large field of view, but to have good binocular vision, with both eyes at once. These are primarily birds of prey and owls, since they need to estimate the distance to prey. Their eyes are close-set, and the intersection of the visual fields is quite wide. At the same time, the narrow overall field of view is compensated by the mobility of the neck. Of all bird species, binocular vision is best developed in owls, and they can turn their heads 270 °.

To focus the eyes on an object during rapid movement (intrinsic, or object, or total), good accommodation of the lens is needed, that is, the ability to quickly and very quickly change its curvature. The eyes of birds are equipped with a special muscle that changes the shape of the lens more effectively than in mammals. This ability is especially developed in birds that catch prey under water – cormorants, kingfishers. In cormorants, the ability to accommodate is 40-50 diopters, and in humans 14-15, although some species, such as chickens and pigeons, have only 8-12 diopters. Diving birds are also helped to see under water by a transparent third eyelid that covers the eye – a kind of goggles for scuba diving.

Everyone must have noticed how brightly colored many birds are. Some species – tap dances, linnets, robins, in general, are not brightly colored, have areas of bright plumage. In others, bright body parts appear during the mating season, for example, male frigatebirds inflate a red throat sac, and in puffins, the beak becomes bright orange. Thus, even by the coloration of birds, it can be seen that they have well-developed color vision, unlike most mammals, among which there are no such elegant creatures. In mammals, primates are the best at distinguishing colors, but birds are even ahead of them, including humans. This is due to some features of the structure of the eyes.

There are two main types of photoreceptors in the retina of mammals and birds – rods and cones. Rods provide night vision, in the eyes of owls they predominate. Cones are responsible for daytime vision and color discrimination. Primates have three types (they perceive red, green and blue colors known to all ophthalmologists and color correctors), other mammals have only two. Birds have four types of cones with different visual pigments – red, green, blue, and violet/ultraviolet. And the more varieties of cones, the more shades the eye distinguishes (Fig. 2).

Unlike mammals, each cone of birds contains another drop of colored oil. These drops act as filters – they cut off part of the spectrum perceived by a particular cone, thereby reducing the overlap of reactions between cones containing different pigments, and increasing the number of colors that birds can distinguish. Six types of oil droplets have been identified in cones; five of them are mixtures of carotenoids that absorb waves of different lengths and intensities, and in the sixth type there are no pigments. The exact composition and color of the droplets vary from species to species: they may provide a fine-tuning of vision so that its capabilities are best suited to habitat and feeding behavior.

The fourth type of cone allows many birds to see ultraviolet color, invisible to humans. The list of species for which this ability has been experimentally proven has grown greatly in the last 35 years. These are, for example, ratites, waders, gulls, auks, trogons, parrots and passerines. Experiments have shown that areas of plumage displayed by birds during courtship are often ultraviolet in color. To the human eye, about 60% of bird species do not have sexual dimorphism, that is, males and females are outwardly indistinguishable, but the birds themselves may not think so. Of course, it is impossible to show people how birds see each other, but you can roughly imagine this from photographs where the ultraviolet areas are tinted with a conventional color (Fig. 3).

The ability to see ultraviolet color helps birds find food. Fruits and berries have been shown to reflect ultraviolet rays, making them more visible to many birds. And kestrels, perhaps, see the paths of voles: they are marked with urine and excrement, which reflect ultraviolet and due to this become visible to a bird of prey.

However, having the best perception of color among terrestrial vertebrates, birds lose it at dusk. To distinguish colors, birds need 5 to 20 times more light than humans.

But that’s not all. Birds have other abilities that are inaccessible to us. So, they see fast movements much better than people. We do not notice flickering at a speed greater than 50 Hz (for example, the glow of a fluorescent lamp seems to us to be continuous). The temporal resolution of vision in birds is much higher: they can notice more than 100 changes per second, for example, in the pied flycatcher – 146 Hz (Jannika E. Boström et al. Ultra-Rapid Vision in Birds // PLoS ONE , 2016, 11(3): e0151099, doi: 10.1371/journal.pone.0151099). This makes it easier for small birds to hunt insects, but, perhaps, makes life in captivity unbearable: the lamps in the room, according to a person, normally luminous, flicker disgustingly for a bird. Birds are also able to see very slow movement, such as the movement of the sun and stars across the sky, inaccessible to our naked eyes. It is assumed that this helps them navigate during flights.

Colors and shades unknown to us; circular review; switching modes from “binoculars” to “loupe”; the fastest movements are clearly visible, as if in slow motion… It’s hard for us to even imagine how birds perceive the world. One can only admire their capabilities!

How to store Stillavit? | What and how to store

The drug is available as an ophthalmic solution for eye care. A small course of Stillavit can relieve the eyes of the feeling of “dryness”, remove irritation of the cornea and relieve fatigue from prolonged visual stress. Due to the mild action of the components, the drops are also suitable for those people who experience discomfort when wearing contact lenses.

Remarkable feature of the solution – no aggressive preservatives , which reduces the likelihood of allergic reactions. This increases the level of requirements for the storage of the drug. This circumstance must be taken into account so that the action of the components retains a healing character during the entire period of the “life” of the solution.

Contents:

• Forms
• How to store the drug according to the instructions?
• How to identify a spoiled product?

Forms

The agent is produced in Russia by the Ophthalm-Renaissance Company (Moscow). The only release form: drops . The solution is contained in vials made of polymeric material, equipped with a stopper-dropper and a screw cap. Bottle volume: 10 ml .

The action is due to the properties of the active ingredients:

1. Sodium hyaluronate at a concentration of 1.60 mg per 1 ml of solution. Polysaccharide of plant origin obtained by biotechnological method. Physiological, present in large quantities in the corneal endothelium.
2. D-panthenol – 10 mg/ml. Vitamin B5, precursor of pantothenic acid.
3. Sodium chondroitin sulfate – 0.50 mg/ml. Physiological polysaccharide; stimulates the synthesis of hyaluronic acid.

Among the auxiliary components of the solution: disodium EDTA (solvent), sodium tetraborate (antiseptic), sodium salts of phosphoric acids (emulsifier), sodium chloride and water.

The solution is produced under aseptic conditions, which ensures its sterility.

The ability of polysaccharide compounds and pantothenic acid to bind a large number of water molecules provides a moisturizing and lubricating effect of drops. The solution has the necessary viscosity and good adhesive properties. When it enters the anterior part of the eye, it forms a kind of tear film there, which persists when blinking and does not blur vision. Vitamin B5 has a powerful reparative effect, which improves the condition of the cornea and conjunctiva of the eye.

The solution is instilled from 2 to 10 times a day in case of “dry eye” syndrome, large visual loads (computer work, watching TV) to relieve corneal irritation from dust, bright light, wind and other factors.

The solution can be used while wearing any type of contact lens. Its use speeds up the process of adaptation to lenses for “beginners”. In people who have a long wearing experience, Stillavit reduces discomfort from contact of the lens with the eye. As a result of instillation, the eyes are moistened, the condition of the cornea and the tear film covering it is stabilized, which significantly improves the tolerability of contact means of vision correction.

How to store the drug according to the instructions?

The manufacturer guarantees the safety and effectiveness of the solution only within the specified expiration date and subject to the prescribed storage conditions. The necessary information can be found on the packaging of the product, in the instructions and on the bottle itself.

Basic storage requirements for Stillavit solution are given in the table:

Shelf life	Temperature rating	Humidity
2 years; after opening – 1 month	+5 to +25 °C	Up to 80%

The purchased drug should be kept in its original packaging, removing it from there only for the instillation procedure. It is recommended to write down the date of opening of the vial, so as not to miss the end of the 30-day expiration date .

Do not store the solution pack in the bathroom – the humidity is too high there. A suitable place for Stillavit can be a cool living room or a medicine compartment on the side of the refrigerator.

An important condition for maintaining the sterility of the solution is hygiene during instillation of . Wash your hands thoroughly with soap before the procedure. This simple action will not only protect your eyes from possible bacteria from your hands, but also protect the solution itself from contamination. During the introduction of drops into the conjunctival sac, the tip of the dropper should not come into contact with either the fingers or the eyelid. After use, the bottle should be tightly closed with a cap.

How to identify a spoiled product?

The drug should be carefully examined at the time of purchase.