Eye: structure
The eyes are located in the depressions of the skull, called the eye sockets, the eye is strengthened here with the help of four direct and two oblique muscles that control its movements. The human eyeball has a diameter of about 24 mm and weighs 6 to 8 g. The eyeball is formed by three membranes of the eyeball and is covered with conjunctiva in front.
The wall of the eye consists of three concentric layers:
1. sclera and cornea. Outside the cornea protects the conjunctiva – a thin transparent layer of cells, transient in the epithelium of the eyelids. Conjunctiva does not enter the corneal area covering the iris. The eyelids protect the cornea from mechanical damage, and the retina from too bright light. The outer surface of the cornea is covered with a thin layer of tear fluid.
2. choroid, ciliary body, lens and iris.
3. the retina. The retina is the inner lining containing photoreceptor cells (rods and cones), as well as the body and axons of the neurons that form the optic nerve. In the place where the optic nerve comes out of the eye, the retina does not contain any rods or cones, this place is called a blind spot of the retina. The most sensitive area of the retina, containing only cones, is the central fossa fossa. The beam of light is focused on it most accurately.
The shape of the eye is maintained by hydrostatic pressure (25 mm Hg) of aqueous humor and vitreous.
The outer shell of the eyeball, the sclera, is under conjunctiva. It consists mainly of collagen fibers, usually affected by autoimmune diseases.
Medium, vascular, shell provides the production and outflow of aqueous humor. The defeat of the choroid is most often caused by immunocomplex allergic reactions and allergic reactions of the delayed type.
The inner shell of the eyeball, the retina, consists of nerve elements and is a peripheral part of the visual analyzer.
The conjunctiva is the mucous lining the posterior surface of the eyelids and the anterior surface of the sclera. It consists of epithelium and connective tissue basis. Normally, mast cells (about 6000 / mm-3) lymphocytes and granulocytes are detected only in the stroma of the conjunctiva, directly under the epithelium. When inflammation occurs, for example, in spring conjunctivitis, conjunctivitis with papilla hyperplasia, these cells appear in the epithelium.
Conjunctiva is rich in lymphatic vessels. The lymph flows from the lateral part of the conjunctiva to the parotid lymph nodes located in front of the auricle trestle, from the medial lymph node to the submandibular lymph nodes. The membranes of the eyeball are devoid of lymphatic vessels.
The vascular membrane and its derivatives – the iris and ciliary body – contain a dense network of vessels. The ciliary body produces aqueous humor, which, like urine and CSF, is a plasma filtrate.
In allergic diseases of the eye can affect any of the membranes of the eyeball. Conjunctiva and tear film on its surface are the first barrier to infection, airborne allergens, organic and inorganic compounds.
Eyes: ophthalmologic examination
First examine the eyelids, then the conjunctiva.
When conjunctivitis is defined: edema, hyperemia, hypertrophy of the papillae and follicles on the conjunctiva of the eyelids and the eyeball. The follicles are larger than the papillae, have the appearance of colorless, grayish or yellow grains ranging from tenths to a few millimeters, do not have their own blood vessels. In the center of each papilla, on the contrary, there is a vessel. When conjunctivitis necessarily palpate the parotid and submandibular lymph nodes: their increase is characteristic of infectious conjunctivitis and is not found in allergic conjunctivitis. Then, tearing, presence and character of discharge from the eyes are evaluated. With uveitis and cataract ophthalmoscopy.
Uveitis is often observed in autoimmune diseases, cataracts – in allergic diseases and long-term treatment with corticosteroids.
In the study of the anterior chamber of the eye assess the nature of the aqueous humor. The watery moisture may contain blood, which is evenly distributed in the anterior chamber or settles at its bottom, or pus, which usually settles at the bottom of the chamber. If the anterior chamber is shallow, glaucoma should be suspected. In this case, mydriatics are contraindicated. A rough estimate of the depth of the anterior chamber of the eye is possible with side lighting with a pen-flashlight.
Eyes: diseases, symptoms of diseases
Trichiasis – the growth of eyelashes in the direction of the eyeball – is caused by the deformation of the cartilage of the upper or lower eyelid, which leads to the twisting of the eyelid.
Constant contact of the eyelashes with conjunctiva leads to conjunctivitis, possibly corneal damage.
Tearing can be a consequence of increased production of tear fluid in case of allergies or obstruction of the tear ducts. The latter is often observed in chronic sinusitis and rhinitis. If you suspect a violation of the outflow of tear fluid in the eye instilled 2% solution of fluorescein. Normally, the dye disappears after 1 min.
Subconjunctival hemorrhage occurs with severe friction of the eyelids, vomiting, coughing, straining, often occurs without cause. With frequent subconjunctival hemorrhages, it is necessary to examine the blood coagulation system.
Pingvecula is a yellowish plaque on the conjunctiva of the eyeball, often located medially from the cornea. It occurs as a result of subepithelial deposition of collagen and proliferation of connective tissue, usually asymptomatic. With age, the pingvecula increases. The pinguecula is often confused with pterigia, which is a triangular proliferation of the conjunctiva that crawls onto the cornea from the medial side.
Flicheng – a small infiltrate in the form of a grayish node of a rounded shape, located in the region of the limbus, is often observed with tuberculosis, a staph infection, exhaustion.
Blepharitis is an inflammation of the eyelids.
Chalazion is a chronic granulomatous inflammation of the meibomian gland.
Barley – a small abscess on the conjunctiva or the skin of the eyelid, occurs as a result of purulent inflammation of the sebaceous gland.
Episcleritis and scleritis – inflammation of the outer membrane of the eyeball – sclera.
The amarotic cat’s eye, the white pupil, is observed in cataracts, Chediak-Higashi syndrome, retinoblastoma and retrolental fibroplasia.
Eyes: diseases, side effects of drugs
Side effects of agents used to treat eye diseases.
Beta-blockers for local use prescribed for glaucoma. It is assumed that they reduce the production of aqueous humor in the anterior chamber of the eye, which, in turn, leads to a decrease in intraocular pressure. Betaxolol is used as beta1-adrenergic blockers, – and nonselective beta-adrenergic blockers – levobunolol, metipranolol and timolol.
All beta-blockers for local use can cause bronchospasm, as they, bypassing the liver, immediately enter the lungs. However, beta1-blockers cause this complication much less frequently than non-selective beta-blockers.
Adverse reactions to the on / in the introduction of fluorescein during fluorescein angiography develop in 5% of patients. In 50% of them, these reactions develop repeatedly. Since the frequency of deaths in fluorescein angiography is 1: 220,000, and more than 200,000 such studies are conducted in the United States each year, an average of at least 1 person dies from fluorescein in the United States. When on / in the introduction of fluorescein anaphylactoid reaction develops, which in 2.9% of patients is accompanied by nausea, in 1.2% – vomiting, in 0.2% – hyperemia of the skin and urticaria and can lead to shock. It has been shown that with on / in the introduction of fluorescein increases the level of histamine in serum.
Skin tests to identify patients with a high risk of reaction to fluorescein are not informative. Avoid repeated reactions to fluorescein, using schemes for the prevention of anaphylactoid reactions to radiopaque substances, as a rule, fails.
Glaucoma: causes, symptoms, diagnosis and treatment of glaucoma
The term glaucoma implies an extensive group of diseases that are characterized by:
- increased intraocular pressure (IOP)
- damage to the optic nerve head, as well as retinal ganglion cells
- narrowing the field of view
Glaucoma may occur regardless of age, but is most common in the elderly or senile.
Glaucoma is considered one of the main causes of irreversible blindness in the world according to the World Health Organization (WHO).
Intraocular fluid and ways of its outflow
Intraocular fluid (hereinafter VGZH) plays a huge role in maintaining the level of intraocular pressure. It is one of the sources of nutrition for intraocular structures (lens, cornea, trabecular apparatus, vitreous humor).
It is produced by the VGZH processes of the ciliary body, located behind the iris, and is collected in the back chamber of the eye. Next, most of the liquid, washing the lens, flows through the pupil, enters the anterior chamber and passes through the eye drainage system (trabecula and Schlemm’s canal), which is located in the corner of the anterior tail chamber. From the drainage system of the eye, the VGZH enters the output collectors (graduates), and then into the superficial veins of the sclera.
In this way, about 85% of the intraocular fluid flows, but there is another way of outflow, which flows about 15%.
The HAH may exit the eye, seeping through the stroma of the ciliary body and the sclera into the veins of the choroid and sclera. This outflow pathway is called uveoscleral.
There is a certain equilibrium between the production of IGL and its outflow. If this balance is disturbed, the level of intraocular pressure changes, which is a prerequisite for the development of glaucoma.
Causes and mechanisms of development of glaucoma
Glaucoma is a multifactorial disease, for the development of which a number of causes (risk factors) are needed:
- heredity
- individual anatomical features or abnormal structures of the eye
- pathology of the cardiovascular, nervous and endocrine systems.
Various combinations of these risk factors trigger the mechanism for the development of glaucoma, which can be represented as stages:
- increased production of intraocular fluid and / or deterioration of its outflow from the cavity of the eyeball;
- an increase in intraocular pressure (IOP) is higher than the tolerant (tolerable) for the optic nerve;
- ischemia (impaired blood supply) and hypoxia (lack of oxygen) of the optic nerve head;
- development of glaucomatous optic neuropathy followed by
- atrophy (death) of the optic nerve.
Forms of glaucoma
The following main types (forms) of glaucoma are distinguished:
- congenital glaucoma:
- primary early congenital glaucoma,
- infantile congenital glaucoma,
- juvenile glaucoma,
- concomitant congenital glaucoma
- Adult primary glaucoma:
- primary open angle glaucoma (POAG) – multifactorial disease associated with involutional and age-related changes in the eye)
- primary angle-closure glaucoma (PZUG) – (the main cause of the disease is the closure of the anterior chamber angle, where the drainage system of the eye is located, by the iris root)
- secondary glaucoma in adults: (a consequence of other ocular or somatic diseases, in which there is an involvement of structures involved in the production or outflow of IGL)
Symptoms of glaucoma
Predominantly, glaucoma is asymptomatic, and the patient notes a decrease in vision, when already 50% of the optic nerve fibers are permanently damaged.
Non-specific symptoms of glaucoma are:
- blurred vision
- pain
- rez
- feeling of heaviness in the eyes
- narrowing of the field of view
- blurred vision in the dark
- “rainbow circles” before the eyes when looking at the source of light
Nonspecific symptoms are called because they may be characteristic of other ophthalmologic diseases.
In case of closed-angle glaucoma and the onset of an acute attack, the symptoms are severe: severe eye pain, headache, redness of the eye, nausea, vomiting.
But if any of the above symptoms appear, you should immediately consult a doctor.
Diagnosis of glaucoma
For the diagnosis of glaucoma and determine the method of treatment of glaucoma, it is necessary to conduct a thorough diagnostic examination, which should include:
- visometry (determination of visual acuity)
- refractometry (determination of the optical power of the eye – refraction)
- perimetry (definition of peripheral vision)
- tonometry (determination of intraocular pressure)
- biometrics (determining the depth of the anterior chamber, the thickness of the lens, the length of the eye)
- biomicroscopy (examination of tissues and media of the eye with a slit lamp)
- gonioscopy (study of the structure of the anterior chamber angle)
- ophthalmoscopy (fundus examination with assessment of the state of the optic nerve and retina)
Glaucoma treatment
Conservative treatment of glaucoma includes drugs that reduce the production of intraocular fluid and / or improve its outflow, hemodynamic (improves blood flow) and neuroprotective (protecting nerve fibers) drugs.
These drugs are prescribed only after a diagnostic examination by an ophthalmologist.
With insufficient effectiveness of conservative therapy (increased IOP, narrowing of the visual field, progression of optical neuropathy), surgical treatment is indicated.
Surgical treatment of glaucoma is aimed at eliminating intraocular blocks (obstacles) in the path of intraocular fluid movement or at creating a new outflow path.
There are many types of operations for glaucoma, but the most successful are:
non-penetrating deep sclerectomy
– with drainage of the anterior chamber angle
– without drainage of the anterior chamber angle
After cutting the conjunctiva and the formation of superficial and deep scleral flaps, the Schlemm canal’s outer wall is removed, thus enhancing the outflow of intraocular fluid through the drainage system of the eye. Sometimes, in the area of excision of the Schlemm’s external wall, drainage is implanted to enhance the effectiveness of the operation.
The advantages of this operation:
- painlessness
- local drip anesthesia
- atraumatic
- performed without penetration into the cavity of the eye, which allows to avoid a number of complications (a sharp decrease in IOP, bleeding, detachment of the choroid, etc.)
Non-penetrating deep sclerectomy is a highly effective method for the surgical treatment of open-angle glaucoma.
penetrating deep sclerectomy
– with drainage of the anterior chamber angle
– without drainage of the anterior chamber angle
– with valve implantation
After cutting the conjunctiva and forming a superficial scleral flap, deep scleral layers are excised, then the anterior chamber is opened and part of the iris is excised, which allows the intraocular fluid to circulate freely in the anterior and posterior chambers of the eye. To enhance the efficiency of the outflow of IHL from the eye, a drainage or valve is implanted in the area of the operation.
Penetrating deep sclerectomy is a more traumatic operation, but its effectiveness is indisputable with angle-closure glaucoma and with the ineffectiveness of a previously non-penetrating operation.
It is worth remembering that timely diagnosis and the appointment of adequate conservative or surgical treatment allows you to maintain high vision in patients with glaucoma for a long period.