Contained in the orbit, the eye is made up of the eyeball and its appendages (eyelids, lacrimal glands, etc.). Its function is to receive light and to transform it into a nervous message which is transmitted to the brain by the optic nerve. It works like a camera.
The three tunics of the eyeball
The external tunic, the liquids that nourish and protect it
The external tunic includes the sclera and the cornea.
The sclera gives the eye its white color and protects it.
The cornea is the main lens of the eye. It allows light rays to pass through it by changing their direction: this is the phenomenon of refraction. The cornea ensures about 80% of the refraction.
It is nourished by the aqueous humor and is permanently humidified by tears, secreted by the lacrimal glands distributed by the beating of the eyelids.
The intermediate tunic or uvea
It’s composed of the iris, the ciliary body and the choroid.
The iris varies the opening of the pupil (between 2.5 and 7 mm) in order to regulate the amount of light that enters the eye.
This avoids blindness in full sun, and allows to capture the few rays at night.
The iris gives the eye its color.
The ciliary body extends the iris backwards and joins the choroid.
The choroid is a vascular layer: it is very rich in blood vessels to feed the photoreceptors of the retina.
It is impregnated with a black pigment, melanin, which transforms the interior of the eye into a dark room. It absorbs the light rays that are useless for vision.
The inner tunic
The inner tunic or retina is the layer sensitive to light thanks to the photoreceptors (cones and rods) it contains.
The rods, approximately 130 million, are located in periphery and are very sensitive to the light. They allow night vision. The cones, about 5 to 7 million, are located in the fovea, the most sensitive part of the retina. They allow day vision and are very sensitive to colors.
The muscles of the eye
The oculomotor muscles
Six oculomotor muscles, attached to the outside of the sclera, allow the movement of the eye in the orbit. A seventh one controls the upper eyelid.
Upper rectus muscle (upward, inward and counterclockwise movement)
Inferior rectus muscle (downward, inward and clockwise movement)
Inner rectus (inward movement)
External rectus (forward movement)
Small oblique (upward, outward and clockwise movement)
Large oblique (downward, forward and counterclockwise movement)
The ciliary muscles
At the limit of the iris and the choroid, they vary the convergence of the lens: by modifying its curvature, the lens makes it possible to focus the light on the retina..
Conjunctivitis is an inflammation of the tunic that covers the white of the eye and the inside of the eyelids: the conjunctiva. It is therefore a superficial inflammation of the eye in its front part, clearly visible, associated or not with an infection. The conjunctiva is transparent and fragile, but it is quickly reconstituted. It is a mucous membrane, like those found in the mouth, for example.
The causes of conjunctivitis are very varied. Irritants” reach the conjunctiva through the air, water, fingers, handkerchiefs, eyelids, tears, nose, sinuses, blood or because “it has to come out of our eyes”.
When the eyes have been exposed to air currents, sea or pool water, dust, etc., it is recommended to preventively flood them with saline solution in order to eliminate the “irritating agent” and thus avoid conjunctivitis.
Signs of conjunctivitis:
The eyes are red, painful, watery…
The eyelids are often swollen and the eyelashes stuck by more or less abundant secretions.
Secretions can flow more or less abundantly from the eyes, disturbing the sight, with, sometimes, itching.
Conjunctivitis can be accompanied by keratitis, damage to the eyelids or lacrimal passages.
Contagious, it usually follows a viral infection, such as the flu. There are often swollen glands in the neck area and a very red and watery eye. It is advisable to be particularly vigilant in case of herpes, this affection being as painful as dangerous for the eyes, and to consult urgently. Herpes is very contagious and the simple contact of fingers is enough to infect the eyes.
During the visit to the ophthalmologist, the diagnosis of viral conjunctivitis is made and a treatment is prescribed for several days or even weeks, depending on the severity of the infection.
Bacterial conjunctivitis is an infection of the conjunctiva that resembles an “eye cold” with abundant secretions that stick to the eyelashes, redness and pain.
It is contagious and may require a laboratory sample to identify the causative germ. The most widespread on the planet, by far, is trachoma due to the microbe Chlamydia trachomatis, responsible in many cases for blindness… and infecting almost the entire population in the poorest countries of the world. The ophthalmologist will determine the origin of the conjunctivitis and prescribe a treatment adapted to the germ in question.
Allergic Conjunctivitis Such conjunctivitis can occur as part of a general allergy, such as hay fever. It can also affect only the eyes, such as cat hair allergy.
The eyes are often red, watery, swollen and very itchy. The causes of such an allergy are varied, from pollens to strawberries to cosmetics to dust mites, and finding the trigger – the only way to prevent a relapse – may require a thorough investigation.
It is up to the ophthalmologist to confirm that the conjunctivitis is indeed allergic and to prescribe an appropriate treatment.
A lack of water in the tears can trigger dry conjunctivitis with dry eye. The tears become greasy and no longer lubricate the ocular surface sufficiently. The eyelids act like windshield wipers on a dry windshield. The dry eye is not sufficiently cleaned of dust and ends up being irritated, which causes burning, a feeling of sand in the eyes, red eyes that are annoying, are dazzled and tire quickly.
The eye is painful when waking up because the lachrymal glands sleep at night and the eyelid ends up sticking slightly on the ocular surface.
Sticky eyelids in the morning should be gently opened by spraying them with warm water. Sometimes the irritation is so severe that one wakes up much too early.
Dry eyes can be the result of working conditions: air-conditioned atmosphere, poor lighting quality, prolonged work on a screen. They are also sometimes due to hormonal problems or rheumatism.
The treatment prescribed by the ophthalmologist consists of making up for the missing tears and trying to bring them back.
This conjunctivitis is caused by poor flow of tears, which stagnate and get infected easily in babies. Everything is too small in them, including the tear duct that carries tears out of the eyes. And any stagnant fluid gets infected.
When tears stagnate in the eye, the tear “lake” becomes a “pond”. In most cases, everything settles spontaneously with growth, and a complete recovery can be observed around the age of one year. The ophthalmologist will prescribe an appropriate treatment or will propose a surgical intervention.
Conjunctivitis in contact lens wearers:
This is a sneaky conjunctivitis to be treated very vigorously from the first symptoms, because it can lead to complications in the form of keratitis or a serious corneal abscess.
This reminds me of the case of a young woman who went on vacation with daily disposable lenses. She did not have enough lenses to complete her stay. She kept the last pair of lenses in her eyes for several days, and got a sneaky corneal abscess under the “spoiled” lens.
She almost lost her eye. She will no longer be able to wear contact lenses and even Lasik surgery has become impossible in her case.
Following the instructions given with each type of contact lens, and in particular the recommended period of use, will allow you to bear wearing lenses for a very long time, or even for life.
It is important to avoid sleeping with your contact lenses, except for those designed for this purpose. To be on the safe side, it is advisable to remove them for 48 consecutive hours every month. You should also put them in a dry case at night, because the permanent humidity favors the development of mycosis and conjunctivitis.
To improve ocular comfort, they can also be placed with a drop of calendula D4 or Euphrasia D3 eye drops in the lens. In case of dry eyes, it is recommended to moisten the eyes with the same eye drops several times a day, whenever dryness is felt.
There are other types of conjunctivitis: a visit to the ophthalmologist is necessary in all cases to receive the right diagnosis and treatment.