Ultrasound examination (ultrasound) completes the ophthalmological examination of the patient because it is contact. And any microdamage to the cornea can distort the readings of autorefractometry or aberrometry.
A-scan (ultrasound biometry) determines the size of the anterior chamber of the eye, the thickness of the lens and the anteroposterior segment (PZO - the anteroposterior size of the eye) with an accuracy of hundredths of a millimeter. With myopia, the eye increases, which is fixed by the apparatus. PZO is used even in identifying the degree of progression of myopia. PZO is normal 24 mm (Fig. 15).
Rice. 15. The size of the eyeball. The length of the anteroposterior segment of a normal eyeball practically coincides with the diameter of a five-ruble coin
B-scan is a conventional two-dimensional ultrasound of the eye. It is possible to diagnose retinal detachment (an urgent operation is necessary, laser correction is at best delayed for a long time), destruction of the vitreous body, intraocular tumors, etc.
Pachymetry. Measurement of the thickness of the cornea. The same indicator that most often supplies contraindications to laser correction. If the cornea is too thin, correction is often not possible. Normal corneal thickness at the center is 500–550 micrometers (~ 0.5 mm). Now there are not only ultrasound, but also optical pachymeters, which measure the thickness of the cornea without touching it.
Conclusion
All of the above are only the main stages of an ophthalmological examination. There can be a lot more research and apparatus, especially if you are found to have any kind of eye disease. There are optional but desirable examinations that I decided not to mention here (such as determining the leading eye, deviation, etc.).
After the end of the ophthalmological examination, the doctor makes a diagnosis and answers your questions, the main one of which is: "Can I do laser correction?" It is extremely rare that situations arise in which laser correction is necessary for medical reasons (for example, when there is a large difference in the "pluses" or "minuses" between the eyes).
Features of filling out a consulting opinion
After the examination, the patient is given a consultation report, which reflects the main results, diagnosis and recommendations. Sometimes very short, sometimes an impressive work on several sheets, including various prints and photographs. Whoever is lucky. The volume does not mean anything here. However, you can glean some useful information from it. Let me give you an example.
Consulting Opinion No. ....
Ivanov Ivan Ivanovich. Date of birth 01.01.1980.
Examined in the clinic "Z" 01.01.2008.
Complains of poor distance vision since the age of 12. The last five years, the progression of myopia is not noted, which is confirmed by the data from the outpatient card. Prophylactic retinal laser coagulation was performed in both eyes in 2007. Has worn soft contact lenses daily for the past 3 years. I took them off for the last time 7 days ago. Denies hepatitis, tuberculosis, other infectious and general somatic diseases, allergy to medicines.
For a narrow pupil:
OD sph –8.17 cyl –0.53 ax 178 °
OS sph –8.47 cyl –0.58 ax 172 °
In conditions of cycloplegia (for a wide pupil):
OD sph –7.63 cyl –0.45 ax 177 °
OS sph –8.13 cyl –0.44 ax 174 °
Visual acuity.
Currently, a large number of formulas have been developed for the accurate calculation of the optical power of an implantable intraocular lens (IOL). All of them take into account the value of the anteroposterior axis (PZO) of the eyeball.
The contact method of one-dimensional echography (A-method) is widespread in ophthalmic practice for examining the PZO of the eyeball, however, its accuracy is limited by the resolution of the device (0.2 mm). In addition, incorrect position and excessive pressure of the sensor on the cornea can lead to significant errors in the measurements of the biometric parameters of the eye.
The method of optical coherent biometry (OCB), in contrast to the contact A-method, makes it possible to measure PZO with a higher accuracy with the subsequent calculation of the optical power of the IOL.
The resolution of this technique is 0.01-0.02 mm.
Currently, along with the OKB, ultrasonic immersion biometry is a highly informative method for measuring PZO. Its resolution is 0.15 mm.
An integral part of the immersion technique is immersion of the sensor in an immersion medium, which excludes direct contact of the sensor with the cornea and, therefore, increases the measurement accuracy.
J. Landers showed that partial coherent interferometry, carried out using the IOLMaster device, provides more accurate results than immersion biometry, however, J. Narvaez and co-authors in their study did not obtain significant differences between the biometric parameters of the eyes measured by these methods.
Target- comparative assessment of measurements of the PZO of the eye using IB and OKB for calculating the optical power of the IOL in patients with age-related cataract.
Material and methods... 12 patients (22 eyes) with cataracts, aged from 56 to 73 years, were examined. The average age of the patients was 63.8 ± 5.6 years. In 2 patients, mature cataract (2 eyes) was diagnosed in one eye, immature cataract in the paired one (2 eyes); in 8 patients - immature cataract in both eyes; 2 patients had an initial cataract in one eye (2 eyes). The study of paired eyes in 2 patients was not carried out due to pathological changes in the cornea (post-traumatic corneal leucorrhoea - 1 eye, opacity of the corneal graft - 1 eye).
In addition to traditional research methods, including visometry, refractometry, tonometry, biomicroscopy of the anterior segment of the eye, biomicro-ophthalmoscopy, all patients underwent ultrasound examination of the eye, including A- and B-scanning using the NIDEK US-4000 echoscan. To calculate the optical power of the IOL, PZO was measured using IB on an Accutome A-scan synergy device and OKB on IOLMaster 500 (Carl Zeiss) and AL-Scan (NIDEK) devices.
Results and discussion... PZO ranging from 22.0 to 25.0 mm was registered in 11 patients (20 eyes). In one patient (2 eyes), the PZO in the right eye was 26.39 mm, and in the left - 26.44 mm. Using the method of ultrasound IB, PZO was able to measure all patients, regardless of the density of the cataract. In 4 patients (2 eyes - mature cataract, 2 eyes - localization of opacities under the posterior capsule of the lens) during OKB using the IOLMaster device, PZO data were not determined due to the high density of lens opacities and insufficient visual acuity of patients to fix the gaze. When performing OKB using the AL-Scan device, PZO was not recorded only in 2 patients with posterior capsular cataract.
Comparative analysis of the results of the study of biometric parameters of the eyes showed that the difference between the PZO parameters measured using the IOL-Master and AL-scan ranged from 0 to 0.01 mm (on average - 0.014 mm); IOL-Master and IB - from 0.06 to 0.09 mm (on average - 0.07 mm); AL-scan and IB - from 0.04 to 0.11 mm (on average - 0.068 mm). The data of the IOL calculation based on the results of measurements of the biometric parameters of the eye using the OKB and ultrasonic IB were identical.
In addition, the difference in the anterior chamber of the eye (ACD) measurements on the IOL-Master and AL-scan ranged from 0.01 to 0.34 mm (mean 0.103 mm).
When measuring the horizontal diameter of the cornea (parameter "from white to white" or WTW), the difference in values between the IOL-Master and AL-scan devices ranged from 0.1 to 0.9 mm (average 0.33), and the WTW and ACDs were higher on AL-scan compared to IOLMaster.
It was not possible to compare the keratometric parameters obtained on the IOL-Master and AL-scan, since these measurements are carried out in different parts of the cornea: on the IOLMaster - at a distance of 3.0 mm from the optical center of the cornea, on AL-scan - in two zones : at a distance of 2.4 and 3.3 mm from the optical center of the cornea. The data of calculating the optical power of the IOL based on the results of measurements of the biometric parameters of the eye using the OKB and ultrasound immersion biometry coincided, except for cases of high myopia. It should be noted that the use of AL-scan made it possible to measure biometric indicators in the 3D control mode of the patient's eye movements, which undoubtedly increases the information content of the results obtained.
conclusions.
1. The results of our research have shown that the difference in the measurements of PZO with the help of IB and OKB is minimal.
2. When carrying out immersion biometry, the values of PZO were determined in all patients, regardless of the degree of maturity of the cataract. The use of AL-scan, in contrast to the IOLMaster, allows obtaining PZO data for denser cataracts.
3. There were no significant differences between biometric parameters, IOL optical power indices obtained with the help of IB and OKB.
Ultrasound examination of the eye is an advanced diagnostic method based on the principle of echolocation.
The procedure is used to clarify the diagnosis in case of detection of ophthalmic pathologies and to determine their quantitative values.
What is eye ultrasound?
Ultrasound of the eyeball and orbits of the eye allows you to determine the areas of localization of pathological processes, which can be determined due to the reflection from such areas of the sent high frequency waves.
The method is characterized by fast and simple implementation and almost complete absence of preliminary preparation.
In this case, the ophthalmologist receives the most complete picture of the condition of the tissues of the eye and the fundus, and can also assess the structure of the muscles of the eye and see violations in the structure of the retina.
This is not only a diagnostic, but also a preventive procedure, which in most cases is performed both after surgical interventions and before them in order to assess the risks and prescribe the optimal treatment.
Indications for using this method
- opacities of a different nature;
- the presence of foreign bodies in the organs of vision with the ability to determine their exact size and location;
- neoplasms and tumors of a different nature;
- hyperopia and myopia;
- cataracts;
- glaucoma;
- dislocation of the lens;
- optic nerve pathology;
- retinal detachment;
- adhesions in the tissues of the vitreous body and disturbances in its structure;
- injuries with the ability to determine their severity and nature;
- disturbances in the work of the muscles of the eye;
- any hereditary, acquired and congenital anomalies of the structure of the eyeball;
- hemorrhage in the eye.
In addition, ultrasound can determine changes in the characteristics of the optical media of the eye and estimate the size of the orbit.
And also ultrasound helps to measure the thickness of adipose tissue and their composition, which is necessary information when differentiating the forms of exophthalmos ("bulging").
Contraindications
- open injuries of the eyeball with violation of the integrity of its surface;
- hemorrhages in the retrobulbar region;
- any damage to the eye area (including eyelid injuries).
What does an ultrasound of the eye show: what pathologies can be detected
Ultrasound of the eye shows many ophthalmic diseases, in particular, it is possible to diagnose diseases such as refractive errors (farsightedness, myopia, astigmatism), glaucoma, cataracts, optic nerve pathology, dystrophic processes of the retina, the presence of tumors and neoplasms.
Also, through the procedure, it is possible to control the state of pathologies in the course of treatment, as well as any ophthalmic inflammatory processes and pathological changes in the tissue of the lens.
How is an eye ultrasound done?
In modern ophthalmic practice, several types of ultrasound are used, each of which is designed to perform specific tasks and is done using its own technical features:
In B-mode, anesthesia is not required, since the specialist moves the sensor along the eyelid of the closed eye, and to ensure the normal procedure, it is enough to lubricate the eyelid with a special gel that will facilitate such sliding.
Normal indicators of a healthy eye with ultrasound
After the ultrasound procedure, the specialist hands over the completed patient card to the attending physician, who deciphers the indications.
Normal indications for the procedure are:
Useful video
This video shows an ultrasound of the eye:
Minor deviations of these characteristics are permissible, but if the values go far beyond such indicators, this is a reason to undergo additional examinations in order to confirm the disease and prescribe adequate treatment to the patient.
Causes of myopia
Today this phenomenon is very common. Statistical data state that about a billion of the world's inhabitants suffer from myopia. Ophthalmologists diagnose her at any age. However, for the first time it is found in children from 7 to 12 years old, and the ailment intensifies in adolescence. Between the ages of 18 and 40, visual acuity usually stabilizes. So, let's find out about the causes of myopia.
Briefly about the disease
The second name of the disease used by doctors is myopia. It is a visual impairment in which the patient sees perfectly close objects and poorly those that are at a distance. The term "myopia" was introduced by Aristotle, who noticed that people with poor vision in the distance squint myops.
Speaking in the language of ophthalmologists, myopia is a pathology of refraction of the eyes, when the image of objects appears in front of the retina. In such people, the length of the eye is increased or the cornea has a high refractive power. Therefore, refractive myopia occurs. Practice shows that most often these two pathologies are combined. With myopia, visual acuity decreases.
Myopia is classified as strong, weak, medium.
Why does myopia occur?
Ophthalmologists name several reasons for the development of myopia. Here are the main ones:
- Irregularity of the shape of the eyeball. In this case, the length of the anteroposterior axis of the organ of vision is greater than normal, and when focusing, the light rays simply do not reach the retina. The elongated shape of the eyeball is a stretching of the back wall of the eye. This state of the vision system can change the fundus, for example, contribute to retinal detachment, myopic cone, dystrophic disorders in the macular zone.
- Excessive refraction of light rays by the optical eye system. At the same time, the size of the eye corresponds to the norm, however, strong refraction forces the light rays to converge in focus in front of the retina, and not traditionally on it.
In addition to these causes of myopia, ophthalmologists also identify factors that contribute to the development of this eye disease. These are the following circumstances:
- Genetic predisposition. Specialists in the field of ophthalmology state that people do not inherit poor vision, but a physiological tendency to it. And the first at risk are those patients in whom both father and mother are susceptible to myopia. If only one of the parents has myopia, then the chances of developing the disease in their son or daughter are reduced by 30 percent.
- Weakening of the scleral tissue often increases the size of the eyeball due to increased intraocular pressure. The consequence of this is the development of myopia in a person.
- Weakness of accommodation, which leads to distension of the eyeball.
- General weakening of the body as the basis for the formation of myopia. It is often the result of both overwork and malnutrition.
- The presence in the body of allergic and infectious diseases (diphtheria, scarlet fever, measles, hepatitis).
- Birth and brain injury.
- Diseases of the nasopharynx and oral cavity in the form of tonsillitis, adenoids, sinusitis.
- Unfavorable conditions for the functioning of the visual system. Ophthalmologists refer to them as excessive stress on the eyes, their overexertion; reading in vehicles that move, in the dark, while lying down; sitting for many hours and without interruptions at a computer or TV screen; poor lighting of the workplace; wrong posture while writing and reading.
All of the above reasons and factors, especially a combination of several of them, contribute to the development of myopia in children and adults.
At the ninth week of intrauterine development, the sagittal size is 1 mm, by 12 weeks it increases to an average of 5.1 mm.
The total eye length of a premature infant (25-37 weeks post-conception) increases linearly from 12.6 to 16.2 mm. The measurement results from a more recent study are shown in the table below.
Newborn Eye Measurement Results with ultrasound examination:
1. The average depth of the anterior chamber (including the cornea) is 2.6 mm (2.4-2.9 mm).
2. The average thickness of the lens is 3.6 mm (3.4-3.9 mm).
3. The average length of the vitreous body is 10.4 mm (8.9-11.2 mm).
4. The total length of the newborn's eye is 16.6 mm (15.3-17.6 mm).
Postnatal growth of the emmetropic eye can be divided into three stages:
1. The phase of rapid postnatal growth, when during the first 18 months of life the length of the eye increases by 3.7-3.8 mm.
2. Slower phase, at the age of two to five years, the length of the eye increases by 1.1-1.2 mm.
3. The slow juvenile phase, which lasts until the age of 13 years, the length of the eye increases by another 1.3-1.4 mm, after which the growth of the eye in length is minimal.
Relationships between different structures of the eye during the growth period. Ultrasound examination results.
Anteroposterior eye size in boys (mm).
Sizes of the oculomotor muscles and sclera
In the first six months of life, the eye grows at its fastest rate. All of its dimensions are increasing. At birth, the size of the cornea and iris is approximately 80% of the size of the cornea and iris of an adult.
The posterior segment, on the contrary, grows to a greater extent in the postnatal period. Consequently, this creates additional difficulties in predicting the results of surgical treatment of strabismus in very young children.
The thickness of the sclera at the age of 6, 9 and 20 months is 0.45 mm, as in the eyes of an adult.
The anteroposterior axis (PZO) is an imaginary line connecting the two poles of the eye and showing a significant gap from the tear film to the retinal pigment epithelium. Among physicians, the anteroposterior axis is the length of the eye and this parameter, together with the refractive power, has a direct impact on the clinical refraction of the eye.
Front-rear axle dimensions:
- for a healthy adult - 22-24.5 mm;
- for a newborn child - 17-18 mm;
- with farsightedness (hyperopia) - 18-22 mm;
- with myopia (myopia) - 24.5-33 mm.
The lowest rates, respectively, are for newly born children. All newborns have farsightedness, intensive eye growth occurs in the first 3 years of life. As they grow older, the child's clinical refraction increases. Mainly already at the age of 10, normal vision is formed and the dimensions of the anteroposterior axis are close to 20 mm.
The genetic factor also plays an important role in the development of the length of the eyeball. Despite the fact that the optimal parameters of the PZO for an adult is 23-24 mm, in some cases, with a large height and weight, healthy indicators can reach 27 mm. Finally, the eyeball, like the anterior-posterior axis, ends its development when the active growth of the entire human body stops.
In the case when the eyes must regularly adapt to intense stress in conditions of insufficient lighting, the dimensions of the anteroposterior axis reach pathological parameters characteristic of such a diagnosis as myopia. Myopia develops in both adults and children, most often schoolchildren, who study in dim light and do not use a table lamp. For long-term professional activities that require special care in working with small objects, high-quality lighting and contrast are imperative. In the absence of the above conditions, especially with weak accommodation, the development of myopia is inevitable.
Determination of the length of the anteroposterior segment is mandatory if refractive errors are suspected in children and adolescents. Studying the length of the PZO of the eye is the only effective method for today that allows to reliably determine the progression of myopia.
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