The pressure inside the eye chambers is determined by the difference in the rate of inflow and outflow of fluid from them. The methods of tonometry (pressure measurement) used in clinical practice are indirect and give a tonometric pressure indicator.
Measurement of intraocular pressure is very important for the diagnosis of glaucoma and timely ophthalmic care for patients.
Maklakov's tonometer in ophthalmotonometry
In domestic ophthalmology, non-contact tonometry methods and measurement of intraocular pressure according to Maklakov are most often used. The latter was proposed in 1884, and entered into wide practice a little later.
Tonometry according to Maklakov consists in a short-term installation of a weight (tonometer) on the cornea of the eye and obtaining an imprint of the contact surface. According to its area, an indicator of intraocular pressure is set.
Besides the territory of the CIS, the method is widely used in China.
Maklakov eye tonometer - completeness and device design
Tonometer kit includes:
- two cylindrical weightsweighing 10 g, widened at the ends with flat end surfaces;
- measurement holder that can hold both weights at the same time;
- 3 measuring rulers for evaluating the diameter of the imprint or the ruler of Professor B. Polyak;
- case.
Loads are hollow inside, contain lead weight. Their end surfaces are made of frosted glass, which allows you to evenly hold the coloring solution.
The holder is needed so that during measurements with fingers not to create excessive pressure on the Maklakov tonometer.
Instructions for working with a tonometer
Before starting work, it is necessary to check the condition of the tonometer. Violation of the integrity of the end pads can cause damage to the cornea of the patient's eyes. In addition, the cylinder must move easily in the gap of the holder.
Treatment of Maklakov tonometers before use consists in wiping the areas with alcohol, after which the device is dried for 15-30 seconds.
Sterilization by boiling in a 2% solution of baking soda for 30 minutes is carried out only in cases of emergency:
- when a patient was examined with signs of inflammation of the conjunctiva;
- in case of a threat in the department of viral keratoconjunctivitis.
Since Maklakov's tonometer is leaky, water can get into it when boiling. So that the results of ophthalmotonometry are not distorted due to changes in the mass of the device, it is dried for an hour or more on sterile gauze.napkin.
The paint applied to Maklakov's tonometer is collargol (colloidal silver with albumin) ground in a mixture of glycerin and water. Bismarck-brown or methylene blue dyes can be used. To cover the plates with paint, a stamp pad is used or a drop of the prepared dye is transferred with a glass rod, and then rubbed with a cotton swab. The latter method is safer in epidemic terms.
Method of studying intraocular pressure with a Maklakov tonometer
Before tonometry, the patient's eyes are anesthetized. To do this, a solution of dicaine is instilled into the conjunctival sac twice with an interval of 2 minutes. The patient covers his eyelids between instillations.
Next, the doctor or nurse performs the following steps in the following order:
- Maklakov's tonometers are disinfected with alcohol, they are dried.
- A thin layer of paint is applied to the tonometer pads.
- The patient lies on the couch without a pillow, slightly raising his chin, fixes his gaze on the index finger of his outstretched hand. The central part of the cornea should be in a horizontal position.
- With the fingers of one hand, the examiner expands the palpebral fissure so that the eyelids do not put pressure on the eyeball.
- With the other hand, using the holder from above, he lowers the Maklakov tonometer with a colored area to the center of the cornea. The weight should come down completely over the eye with all its weight.
- Then the load is quickly lifted and imprinted on paper,moistened with alcohol.
- The study is repeated for the second eye.
- Patient's eyes are washed out of paint with saline and instilled with albucid.
During the lowering of the tonometer on the cornea, the paint on the contact area is washed off with a tear. The result is a ring.
Interpretation of the results of ophthalmotonometry according to Maklakov
The diameter of the light circle on the print is proportional to the degree of flattening of the cornea during the examination. Accordingly, the higher the pressure, the less ink will be removed and, accordingly, the light area of the print will be smaller.
The diameter of the light area is measured with a transparent ruler. The researcher should place it scale down to avoid distortion. The result is evaluated through a binocular loupe. The scale applied to the ruler allows you to immediately convert the result into millimeters of mercury.
When measuring with a regular ruler (up to 0.1 mm), the pressure indicator is calculated as a ratio to the weight of the tonometer: the square of the radius of the print by the number "Pi" and the specific gravity of mercury (13.6).
The norm of eye pressure according to Maklakov is the range of 18-26 mm Hg. st.
Limitations and features of the method
It is not recommended to use Maklakov tonometry in the following cases:
- after eye surgery;
- for an allergic reaction to an anesthetic;
- with inflammation of the eye and membranes.
Maklakov's tonometer exerts pressure on the eyeball that exceeds this indicator in other methods, respectively, the norm of the result shifts upwards. For comparison, the normal eye pressure according to Goldman is 9-21 mm Hg. Art. Therefore, comparing the results obtained by different methods will not be correct.
