Norn test in ophthalmology. Study of tear production and drainage. Qualitative assessment is carried out using methods
Methods for studying tear production
Comprehensive examination of the tear-producing apparatus of the eye includes assessment of the stability of the precorneal tear film and measurement of the secretion of tear fluid (total, as well as, if necessary, main and reflex).
Determine the stability time of the precorneal tear film.
Determine the total amount of secreted tear fluid.
Determine the amount of main (carried out by accessory lacrimal glands) secretion of tear fluid.
Indications
Dry eye syndrome and suspicion of it with normal Schirmer test values.
Contraindications
Similar to those for the Schirmer test.
Preparation
The test strip is prepared as for the Schirmer test. Eye drops with an anesthetic are instilled into the conjunctival cavity.
Methodology
After instilling the anesthetic solution from the lower conjunctival fornix, carefully absorb the tear and the remaining drug with a cotton swab. Then, a strip of filter paper is placed behind the patient’s lower eyelid for 5 minutes (as when performing the Schirmer test) and the result obtained is assessed in the previously described manner.
Interpretation
Normally, at least 10 mm of the test strip is wetted in 5 minutes. Smaller sample values indicate a decrease in the main tear production.
Since the Schirmer test allows you to estimate the volume of total tear production, and the Jones test - the main tear production, the difference in their results characterizes the amount of reflexively released tears (normally - at least 5 mm). However, its “reserve” is significantly higher than this value, since the irritant used in the examined tests (filter paper) is far from the strongest.
Operational characteristics
The sensitivity of both tests (Schirmer and Jones) is satisfactory. False-negative test results are associated with excessive irritation of the cornea due to improper placement of the strip.
The specificity of both tests is very high (provided that the procedure for their preparation is followed).
Factors influencing the result
Erroneous results of the examined tests can be caused by incorrect placement of the test strip, namely its contact with the cornea, excessive irritation of the eyelashes and skin of the eyelid. As a result, excessive stimulation of reflex lacrimation occurs and a false negative test result occurs. For the same reason, opening the eyelids during the examination is also unacceptable. However, the largest number of erroneous conclusions when testing the samples in question is associated with the inadequate quality of the filter paper for preparing the test strip, so it is preferable to use their standard branded kits (see Fig. 8-2).
Complications
Not noted (taking into account contraindications for the test).
Alternative Methods
Method for measuring tear production using a test thread is based on determining the time required to wet a piece of hydrophilic (polyvinol, cotton, etc.) thread placed at one end behind the lower eyelid of the subject (as when performing a Schirmer test). The test result depends on the material and thickness of the test thread used. The method allows you to evaluate both total tear production and its main components.
Lactoferrin test aims to measure the concentration of lactoferrin in tears (it is produced by the lacrimal glands). A decrease in tear production is indicated by a decrease in the concentration of the test protein in tears to 0.92 mg/ml or lower. A simplified method for determining lactoferrin in tears using a portable Lactoplate analyzer has been developed. The method is designed to estimate the amount of main tear production.
Test with sodium fluorescein dilution is based on fluorophotometric observation of the decrease in the concentration of the dye in the conjunctival cavity as it is “diluted” by constantly secreted tears. The test allows you to estimate the amount of main tear production.
Method for assessing the height of the tear meniscus. Using a slit lamp (with a thin slit), the ratio of the vertical and horizontal components of the lower tear meniscus in the area of contact of the free edge of the lower eyelid to the cornea is assessed. Normally, the height of the tear meniscus is 2 times higher than its base. If the ratio in question changes in favor of the vertical component, lacrimation is diagnosed, if horizontal there is a decrease in tear production. The sample serves to measure the volume of fluid present in the conjunctival cavity at the time of examination, which indirectly allows one to assess the main tear production.
Assessment of active patency of the lacrimal ducts
Schirmer test.
Two strips 5 mm wide and 40 mm long are cut out of laboratory filter paper of the “Filtrak” type. Their ends (5 mm) are bent at an angle of 40-45°. The patient is asked to look up and at the same time, with the finger of one hand, the lower eyelid of the right eye is pulled down, and with the other hand, the short curved end of the strip is carefully inserted beyond its ciliary edge in the lateral third of the palpebral fissure. In this case, the curved part of the strip with its end should reach the bottom of the lower fornix of the conjunctiva. Then the same procedure is carried out on the left eye. Immediately after inserting the test strips over the eyelids, start the stopwatch.
After 5 minutes, they are removed and the length of the moistened part (from the bend point) is measured using a millimeter ruler. Normally it is at least 15 mm.
When using other types of filter paper, the regulatory figures will differ. In particular, the results of studies conducted by V.V. Brzhesky and E.E. Somov (1998) showed that the normal wettability of test strips produced by Alkon is already 23 ± 3.1 mm.
Norn's test.
The patient is asked to look down and, pulling the lower eyelid with a finger, irrigate the limbus area for 12 hours with one drop of 0.1-0.2% sodium fluorescein solution. After this, the patient is seated at the slit lamp and, before turning it on, is asked to blink again and then open his eyes wide. Through the eyepieces of a working slit lamp (a cobalt filter must first be introduced into its system), the cornea is scanned in the horizontal direction. The time of formation of the first break in the colored tear film is noted. Most often it occurs in the lower outer quadrant of the cornea. In the course of research conducted by V.V. Brzhesky and E.E. Somov (1998), proved that in healthy people aged 16-35 years, the tear film break time is 21±2.0 s, and in healthy people aged 60-80 years - 11.6±1.9 s.
ADDITIONS
Burn degrees.
1.Hyperemia and chemosis of the conjunctiva, mild pinpoint opacification of the cornea. The surface layers of the epithelium are damaged.
2.Anemization, chemosis, conjunctival erosion, corneal opacity. The epithelium is damaged, with the exception of the germinative layer. The iris is not changed.
3. The conjunctiva is white, the cornea is intensely cloudy. Necrosis of all layers of the conjunctiva, epithelium, Bowman's membrane, and partially the native layer of the cornea. Irritation of the iris.
4. Disintegration of the conjunctiva and superficial layers of the sclera. Intense opacification and disintegration of the cornea. Necrosis of all layers of the cornea. Irritation of the iris.
EXAMPLES OF RESEARCH
OD sph-1.5 cyl -1.0 ax 90 (sph-1.5 - 1.0 x 90)
OS sph -2.0
This prescription means that the right eye requires spherical correction of myopia with a -1.5 D lens; there is astigmatism, which is corrected with a minus cylindrical lens of 1.0 D, while the axis of the cylinder, i.e. inactive meridian, located along an axis of 90 degrees. For the left eye, spherical correction with a minus lens of 2.0 D was prescribed.
OU sph +1.0 +1.5 add
In this case, bifocal lenses with a distance zone of +1.0 D and a near increase of +1.5 D were prescribed for both eyes.
OD Sph −2.0D Cyl −1.0D ax 179
OS Sph −2.8D Cyl −2.0D ax 173
Dp 68 (34.3/33.7)
For the right eye, correction of myopia (myopia) with an optical power of a lens of 2.0 D and correction of astigmatism using a cylindrical lens with a power of -1.0 D with a cylinder axis of 179 degrees is required.
The left eye requires correction of myopia (myopia) with an optical power of a lens of 2.8D and correction of astigmatism using a cylindrical lens with a power of -2.0D with a cylinder axis of 173 degrees.
The interpupillary distance is 68 mm; The distance from the bridge of the nose to the pupil of each eye is indicated in parentheses.
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
4.1. Structure of the tear film
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
4.2. Tear meniscus examination
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
4.3. Study of tear film breakup time using non-invasive methods
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
4.4. Tear Film Breakup Time Study Using Fluorescein
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
The Norn test is a way to test the stability of the precorneal tear film. Very often, this test is performed in ophthalmology to diagnose a disease such as dry eye syndrome. When it occurs, damage to surface structures occurs (as a result of disruption of the stability of the tear film). This disease is characterized by rapid evaporation of tears.
Methodology
Sample (test) Nora is carried out as follows:
- While the test is being performed, the patient should look down.
- The lower eyelid must be pulled back.
- The tear surface of the eye is stained. To do this, use a few drops of sodium fluorescein solution, which is applied to the limbic area of the eye.
- For follow-up, the doctor uses a slit lamp.
Slit lamp
- The patient needs to blink and then keep his eyes wide open.
- The cornea is scanned through the eyepieces of a slit lamp (the illuminating part of which is preliminarily introduced with a blue light filter). Through observation, the doctor records the time it takes for the precorneal tear film to rupture. This is not difficult to do because the tear film is pre-colored.
- The specialist uses a stopwatch to record time. It must be stopped when the film rupture increases or directed rays appear from the area of tear of the tear surface.
- Most often, the tear occurs in the lower outer part of the cornea. This is due to the fact that the surface in the indicated location is much thinner in thickness.
- In order to obtain the most accurate results after the examination, the doctor should conduct the test several times (2 or 3) on each eye. The results obtained must be reduced to the average value.
Interpretation of results
After the test is completed, the specialist examines the results. Numerous studies have been carried out to highlight the normal time of surface rupture depending on the age of the patient.
- If the patient who underwent the test is in the age group from 16 to 35 years, then the normal time for the tear film to break will be considered 21 seconds after the last blink.
- With age, this figure decreases. Therefore, when the patient's age varies from 60 to 80 years, the time of rupture of the precorneal surface at 11-12 seconds will be considered normal.
The doctor can conclude that there is a violation of the stability of the tear film if the break occurs less than 10 seconds after the last blink.
Cost of examination
The study is carried out in ophthalmology clinics. The test is usually carried out by qualified and experienced professionals. The cost of such a service is very reasonable for citizens. The average price in Moscow and St. Petersburg ranges from 300 to 560 rubles.
In most cases of dry eye syndrome, there are problems with the formation of tear fluid. There may also be changes in the composition and drainage of the solution that is produced by the lacrimal glands. To assess the condition of the eyes in this syndrome, not only clinical signs are used, but also a number of diagnostic tests. For example, the Schirmer test is used to determine tear production; the fluorescein instillation test and the Norton test can be performed to study the tear film itself. To establish a diagnosis of dry eye syndrome, it is enough to identify a decrease in the amount of tears produced, as well as disruption (tears, instability) of the tear film.
To carry out the Norm test, a solution (0.1%) of a photosensitizer (sodium fluorescein) is used. You will also need a slit lamp with a blue filter to carry out the test. In this case, the illuminator is limited to a high slit (of medium width), and the angle with respect to the microscope should be 300. To increase the reliability of the examination, you can switch the operation of the slit lamp to the illuminator overheating mode. The overall sensitivity and specificity of the Norna test are quite high.
Methodology
During the Norna test, one drop of fluorescein solution is instilled into the patient's eye (on the limbus area). In this case, the subject’s gaze should be directed downwards, and the upper eyelid should be retracted. Next, you need to blink once, and then open your eyes and try not to make blinking movements. The doctor starts a stopwatch and observes the stained surface of the tear cord through the slit lamp. Particular attention is paid to the cornea, where the tear film breaks, which looks like a dry spot or black hole.
At the moment when the tear in the tear cord increases in size or radial branches appear from it, the doctor must stop the stopwatch. The tear can be located in any area of the surface of the eye, but its favorite location is the lower outer quadrant of the cornea near the tear meniscus. This is due to the fact that in this area the thickness of the tear film is thinnest. To get a reliable result, you need to test 2-3 times for each eye, and then average the obtained values.
Interpretation of results
In healthy people, tear film rupture occurs no earlier than 10 seconds after blinking. If a violation of the integrity of the film is recorded at an earlier date, then there is a violation of the stability of the precorneal tear layer.
The Schrimer test is based on reflex stimulation of tear fluid production, as well as the absorbency of filter paper, which is placed in the conjunctival cavity.
The purpose of the study is to determine the amount of tears that are produced over a certain time.
The Schrimer test cannot be performed in case of an ulcer or fistula of the cornea, extensive erosion of its surface, or in case of perforation of the eyeball.
Methodology
To carry out the test, you must use special filter paper strips. They can be produced in a set or you need to make them yourself (length 40 mm, width 5 mm). The end of the strip at a distance of 5 mm from the edge is bent at an angle of 40-450. Next, the patient is asked to look up, and this curved tip is placed under the lower eyelid of the eye (in the outer third). It is necessary that the edge of the strip touches the bottom of the lower fornix of the conjunctiva, then the bend will be located at the level of the edge of the eyelid. It is advisable to carry out the test on both sides simultaneously.
After administering the strips, the doctor should start the stopwatch and the patient closes his eyes. After exactly five minutes, the strips are removed and the length of the wet part is measured, starting from the point of inflection. If the wetting boundary cannot be established, the strips can be illuminated. When the wet boundary is located obliquely, the average result is taken into account.
Interpretation of results
In healthy patients, 15 mm test strips are wetted for 5 minutes. With a decrease in tear production, the length of the wetted test strip decreases; with hypersecretion of tear fluid, on the contrary, it lengthens significantly, reaching 35 mm within 2-3 minutes. The Schrimer test does not exclude a decrease in the main tear production, which can be masked for a long time by its reflex increase.
Cost of diagnostic procedures
These studies are quite simple to perform and are inexpensive. The price of each of these procedures in eye clinics in Moscow is about 500 rubles.
