The Norn test is one of the methods for diagnosing dry eye syndrome. Dry eye syndrome is a lack of moisture on the surface of the conjunctiva and cornea.
The front side of the eyeball is covered with a thin tear film, which protects the eye from direct exposure to the atmosphere, helps flush out foreign bodies from the eye, provides the cornea with nutrients and oxygen, and has immunoprotective properties. The film breaks, and we blink to renew the tear fluid and restore the film. At the age of 16-35, the film breaks in approximately 21 seconds; with age, this interval decreases and by the age of 60-80 it is already 11.6 seconds. If the tear film breaks in less than 10 seconds, it is considered pathological, and in this case, dry eye syndrome is diagnosed.
The Norn test is a test to determine how long it takes for the tear film to break. The patient is asked to look down, after which, pulling back the lower eyelid with a finger, the ophthalmologist instills a 0.1-0.2% solution of sodium fluorescein, which colors the tear fluid. Next, a scan is performed using a slit lamp and a blue filter. The patient is asked to blink one last time, after which he must look without blinking. This allows the doctor to time the first rupture of the film after blinking. The entire procedure (tinting the film, using a slit lamp and a light filter) is designed so that observing film breakage does not pose a problem.
Also, the Norn test makes it possible to detect pathological changes in the cornea that have already begun.
Try asking your child what a tear is. You will most likely find out that “a tear is simply when we cry.” Meanwhile, not every adult knows: a tear is far from “simple” and, in addition, tears are always present in the eyes, and not just when crying.
The human lacrimal apparatus is a tiny irrigation and drainage system. In a very limited volume near the front of the eyeball, tear fluid must somehow be produced, perform its functions and be discharged along certain drainage paths. Let's try to figure out how this happens.
There are two main structural elements: tear producing and tear draining. From school we remember that “tears are produced by the lacrimal gland,” but this knowledge is incomplete and insufficient. The fact is that the composition of the tear fluid is very complex and must be clearly balanced, since it performs a number of difficult-to-combine functions simultaneously: wetting the anterior surface of the eyeball (which is especially important for the transparent cornea, which would otherwise dangerously dry out when interacting with air oxygen), aseptic removing trapped particles, minimizing friction during movements of the eyeball and, at the same time, protecting tissues from waterlogging and “souring.”
Therefore, the composition of tears includes not only the liquid fractions themselves, but also oily-mucous, hydrophobic ones, and separate structural parts of the tear-producing section are responsible for their secretion. In addition to the main lacrimal gland, located above the eye from the side of the temple, there are also additional lipid and mucin glands of the conjunctiva, the mouths of which extend onto the inner surface of the eyelids adjacent to the eye.
Mixing and uniform distribution of various fractions of tear fluid over the surface of the eyeball occurs when blinking, ensuring constant renewal of a thin, but multi-layered tear film, which protects the cornea, sclera, and conjunctiva from the problems described above. Considering the mobility of the eyeball and the unreliability of surface tension, the film must be renewed quite often: otherwise, tears will appear in it (the fabric dries faster in these areas) and, in addition, the film itself quickly evaporates. Therefore, you should not suppress the natural blink reflex and read these lines, as they say, with an unblinking gaze - it is no coincidence that any system of eye gymnastics for people who constantly work with a computer necessarily includes breaks with intense blinking.
Having given way to a new portion, the waste tear fluid must, of course, go somewhere, otherwise the person would cry for days on end. On the inner wall of the eyelid, at the bridge of the nose, there are drainage entrances to the lacrimal canaliculi, where excess moisture flows. Getting into the so-called lacrimal sac, through the nasolacrimal duct, the liquid is discharged into the nasal cavity, where it is used for additional wetting of the nasal mucosa.
Schirmer test has been practiced for over a hundred years. The only equipment needed for such a study is a narrow strip of highly absorbent paper. In modern ophthalmology, of course, it is not a notebook “blotter” that is used for this purpose, but a specially developed and industrially produced aseptic material. The test consists of placing a five-millimeter edge of an absorbent strip bent at an angle of about 45 degrees between the eye and the lower eyelid (closer to the temple). The fold is located at the edge of the eyelid, and there should be no contact between the paper and the cornea. All that is required of the patient is to sit for five minutes with his eyes closed. After this time, the strip is removed and quickly, taking into account the ongoing soaking, the length of the already moistened section is measured. If it is shorter than 15 millimeters, the secretion of tear fluid is insufficient.
Norn's Test historically younger (it was proposed in 1969) and somewhat more complex. A special illuminating substance is used, sodium fluorescein, a weak solution of which is instilled, pulling the lower eyelid, into the limbal zone. After this, the patient should blink, and then refrain from blinking by force of will. A slit lamp is used as a diagnostic tool (a device widely used for refractometry - diagnostics of the refractive properties of the ocular media). In this case, a cobalt filter is placed in the illumination system, which improves the visualization of fluorescein. The patient looks into the eyepieces of the device while a vertically flat light stream, directed by a rotating mirror, passes along the surface of the cornea. The technique allows the doctor to see breaks in the tear film and record the time of their appearance. To ensure and maintain the water regime necessary for the eye, the film must remain intact for at least 10 seconds after each blinking act.
Drainage (removal) of tear fluid is no less important a process than its secretion. The standard for meaningful and fairly reliable diagnosis of the lacrimal ducts is the so-called. color tests and, if indicated, direct probing of the lacrimal canaliculi.
The Vesta color test is also one of the traditional and proven diagnostic techniques: in two years it will celebrate its centenary. As in the previous method, it requires a sodium fluorescein solution, but in a slightly higher, two percent concentration. After instilling the solution, the patient is asked to tilt his head down for a period, the total duration of which can be 20 minutes or more. If the functional status of the lacrimal ducts is normal, the coloring substance should appear in the nose within the first five minutes after instillation (the test is positive). If this interval is from 6 to 20 minutes, the reaction to the test is considered slow and, finally, if fluorescein does not appear in the nasal cavity after 20 minutes, the test is considered negative and indicates blockage of the lacrimal tract.
If the result is positive, there is no point in continuing the patency study. If drainage is somehow difficult or completely blocked (negative nasolacrimal test), additional diagnostics is necessary.
First of all, an anesthetic is instilled into the eye to eliminate discomfort during further manipulations. Their algorithm is as follows:
Assessment of the patency of the lacrimal canaliculi is carried out using a thin probe, which is inserted with all precautions (to avoid injury); under the anatomical norm, the probe should freely penetrate the lacrimal sac until it touches the adjacent bone wall;
A disinfectant solution of furatsilin, or simply a sterile saline solution, is injected through the lower lacrimal punctum with a syringe (with a blunt cannula instead of a needle). After this, the patient must lower his head again, placing a special container under his chin. The path and nature of the flow of the flushing liquid is of key importance: is it evacuated through the nose freely, comes out in rare drops, or generally flows out in the same way as it was introduced (in some cases, the liquid comes out of another, upper lacrimal opening);
Sometimes it is advisable to conduct an additional Pole test - the so-called. “pump” - which also serves to diagnose the patency of the lacrimal tract. Instill a 3% solution of collargol (this dye preparation also contains silver, known for its antiseptic properties) and wait two minutes. Then the conjunctiva of the lower eyelid is tamponed dry with a cotton ball and immediately after this the area of the lacrimal sac is pressed with a finger (creating pressure similar to a pump, which gives the name to the test). With normal patency of the tubules, the colored collargol should erupt in a small fountain from the lower lacrimal opening - this result is considered positive. Any other option (fluid flows sluggishly, only a microscopic amount appears, or nothing happens at the lacrimal opening at all) indicates impaired or blocked patency and is considered negative.
Schirmer test (determination of tear production) - 500 rub.
Norn test (test of tear film stability) - 500 rub.
The Norn test is a diagnostic technique aimed at determining the stability of the tear film. The procedure is quite simple and does not require any preparation from the patient. During this procedure, a solution of fluorescein or analogs is instilled into the patient’s eye, which stains the tear film of the eye.
After this, the ophthalmologist scans the cornea using a blue filter element and a slit lamp. This approach allows any disruption of the tear film to be identified and appropriate action taken.
The Norn test has become widespread in ophthalmology, since it can confirm or exclude dry eye syndrome in a patient. This condition is fraught with a number of serious complications.
During the diagnostic process, the ophthalmologist can determine the stability of the tear film. It covers the cornea of the eye and performs a number of important functions. They are as follows:
Thinning of the tear film causes discomfort, sand in the eyes, redness and pain, which is fraught with much more serious consequences. By interpreting the results of the Norn test, the doctor has the opportunity to determine the time of tear film rupture, as well as a number of pathological changes in the cornea at the initial stage.
The procedure is simple and does not require special preparation from the patient. All you need to do is visit the ophthalmologist’s office on time. He will be asked to take a sitting position and a 0.1-0.2% solution of sodium fluorescein will be dropped into the eye or special strips with a coloring effect will be used.
Sodium fluorescein is a dye that has found widespread use in medicine for diagnostic studies. It is used with caution, excluding the presence of contraindications in the patient.
After applying the dye, the patient is asked to blink and avoid blinking during the slit lamp examination. An ophthalmologist examines the cornea and records the period of time during which the integrity of the tear film is disrupted. To do this, use a stopwatch, which turns off after the gap has increased.
In the process of interpreting research data, the ophthalmologist compares the results obtained and the Norn test indicators, which in ophthalmology are considered to be the norm. Since the test is carried out at least three times, using drops in each eye, the doctor operates on the average value. When decoding, the patient’s age must be taken into account. The norm is:
The Norn test is performed to determine such an indicator as the time of tear film breakup. This study is needed to confirm or exclude dry eye syndrome, when insufficient tear production occurs and the cornea does not receive the necessary moisture. This pathological condition is dangerous due to complications, in particular, loss of visual acuity. The diagnostic procedure is carried out in a clinic using the latest equipment.
Excessive sitting at a PC and constantly running the air conditioner increases the risk of dry eye syndrome. With this pathology, damage to the superficial elements of the visual system often occurs. The Norn test is required when a person’s normal tear production is disrupted, that is, the number of basal tears decreases. It is carried out quickly, without harming health and without pain. During the research process, a person should look only down at all times. The test is carried out in stages:
After conducting the study three times on each organ, the doctor will calculate the average value, on the basis of which a certain conclusion will be made.
The Norn test must have results accepted as the norm. Often changes occur in the lower part, where the film thickness is minimal. In order to get an accurate result, the specialist conducts this test several times in a row (at least 3 times for each eye). From the obtained figures, the average is determined. The norm for each group of patients is different. It depends on the age category, the main indicators are presented in the table:
Basically, the specialist makes a conclusion about a change in the stability of the precorneal tear film if a breakthrough occurs less than 10 s after blinking.
Because soft contact lenses interact directly with the tear film and require sufficient amounts of tears to wear comfortably, it is necessary to evaluate the tear film quantitatively and qualitatively to help prevent potential problems.
Typically the film thickness is 7 microns
The average volume of tear fluid in the eye is 6 µl
Time for complete evaporation of the tear film 10-20 s
Flashing time is normal - every 5-10 s
To study the tear film, there is a special device - a tiascope, with which you can detect the very initial changes in its structure. However, in everyday practice this is not necessary, so we will focus on the simplest methods to distinguish normality from pathology.
Quantitative assessment of tear fluid can be done using the following methods:
Schirmer test
Qualitative assessment is carried out using the following methods:
Tear meniscus examination
Tear Film Breakup Time Study
The layer of water and dissolved nutrients on the cornea is called the tear film. This film is constantly produced and removed from the surface of the eye. The tear film consists of:
Lipid layer
Water layer
Mucin layer
lipid layer
Provides sliding of the conjunctiva of the upper eyelid along the surface of the eye
Protects the cornea from drying out
aqueous layer
Provides the cornea with oxygen and nutrients
Immune defense (lysozyme)
Flushes foreign bodies out of the eye
mucin layer
Binds the tear film to the cornea
Makes the surface of the cornea even and smooth, thereby ensuring high quality vision
The tear meniscus is a thickening of the tear film along the posterior edge of the lower eyelid. To assess his condition, the biomicroscopy technique is used, if possible, with a “grid”, at high magnification (x25) and avoiding bright lighting so as not to interfere with the tear reflex.
Methodology:
Compare both eyes
Examine before any instillations and manipulations
Examination of the tear meniscus helps assess tear volume:
Normal: meniscus width 0.3 -0.4 mm
Insufficient tear volume - meniscus 1.0 mm
and tear quality:
Normal: the border of the meniscus is smooth, the shape is convex
With pathology: irregular shape and scalloped edge
The study is carried out without the use of any dyes, which eliminates the irritating and tear-causing effects of medications.
The examination is carried out using a special device - a xeroscope, but if it is not available, you can use a regular keratometer and, in this case, the indicator is the time at which the picture of the marks projected on the cornea begins to blur.
The method allows you to assess the stability of the tear film, namely the function of the mucin layer.
Results:
Normal > 30 s
Borderline states: from 10 to 30 s
Pathology< 10 с
This method assesses the stability of the tear film using fluorescein.
After instillation of fluorescein, using a blue cobalt filter of a biomicroscope, we determine the time when the tear film is destroyed on the surface of the cornea, which is visually determined as the appearance of dark spots on a smooth background.
Results:
The norm is from 10 to 45 s
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