Astigmatism: Clinical Guidelines

List of Abbreviations

D – diopter

IOL – intraocular lens

LASIK – Laser-Assisted in Situ Keratomileusis

STCL – soft toric contact lenses

OKL — orthokeratology lenses (rigid gas-permeable orthokeratology contact lenses)

RGPCL – rigid gas-permeable corneal contact lenses

SGPCL – scleral gas-permeable contact lenses

SMILE – Small Incision Lenticule Extraction

DED – dry eye disease

PRK – photorefractive keratectomy

Dk – oxygen permeability of a contact lens. Characterizes the oxygen flux through the contact lens material.

Dk/t is an index of oxygen permeability of a contact lens, characterizing the rate of oxygen molecule penetration through a unit area of the lens over a specific time period. The higher the Dk/t value, the higher the oxygen permeability of the lens

LRI - limbal relaxing incisions

Terms and Definitions

Astigmatism is a combination of two or more refraction values in a single eye; astigmatism is not an independent type of clinical eye refraction, but represents a measure of the non-sphericity of its optical system.

Principal sections (meridians) of an astigmatic eye are two sections (meridians) located at an angle of 90⁰ to each other, in which refraction is the strongest and the weakest.

Sturm's conoid is a schematic description of the light ray path in an astigmatic eye and image formation on the retina.

Irregular astigmatism is astigmatism in which refraction changes within a single meridian.

Regular astigmatism is astigmatism in which refraction remains constant in each principal meridian.

Physiological astigmatism is a small degree of astigmatism capable of self-compensation, which does not affect vision and does not require optical correction.

1. Brief information on the disease or condition

1.1 Definition of the disease or condition

Astigmatism (from Greek a- meaning negation and stigma meaning point) is a combination of two or more refraction values in a single eye. Astigmatism is not an independent type of clinical eye refraction, but represents a measure of the non-sphericity of the eye's optical system [1,2,3,4].

Regular astigmatism is astigmatism in which the refractive power of the eye's optical system varies, but remains constant in two perpendicular meridians (sections), as a result of which a bundle of light rays originating from any point in space and falling on the eye is collected not into a focal point, but into a figure having two focal lines – anterior and posterior, located on the optical axis. These lines, together with the circle of least confusion and the figures of horizontal and vertical ovals located between them, constitute the so-called Sturm's conoid [1,2,3,5,6].

Irregular astigmatism is astigmatism in which the refractive power changes within a meridian, and the bundle of light rays falling on the eye does not form line, circle, or oval figures on the optical axis. Irregular astigmatism develops as a result of eye diseases that deform the shape of its optical surfaces: keratoconus, keratoglobus, corneal scars of various origins, corneal dystrophies, lenticonus, lens subluxation, and other conditions [1,7,8].

Irregular astigmatism requires a special approach to correction and treatment and is not considered in these clinical guidelines.

1.2 Etiology and pathogenesis of the disease or condition (group of diseases or conditions)

Astigmatism is more commonly a congenital condition and is caused by the shape of the ocular refractive surfaces (the shape of the anterior and posterior surfaces of the cornea, the crystalline lens, the irregularity of their curvature, the ratio of refractive power to the optical axis of the eye, and the shape of the posterior pole of the eye), which creates a disparity in the refraction of the principal meridians of the eye [1,3,7].

The development of regular acquired astigmatism is associated with uneven eye growth or changes in the relationship between the optical elements of the eye [8,9]. In addition, regular and irregular astigmatism of the eye can develop as a result of: keratoconus, keratoglobus, corneal dystrophies, lens subluxation, corneal scars of various origins, corneal surgical interventions (including refractive), cataract surgery and other eye surgeries, eyelid diseases, and other causes [7,10,11].

1.3 Epidemiology of the Disease or Condition

Astigmatism is a very common refractive error. In various countries, astigmatism of 0.5 D or more is found in 9.8 – 27.2% of children and in 11.4–67.97% of adults [9,10,11]. Such a variation in the prevalence rates of astigmatism in different countries is likely due to the availability or lack of reliable methods for diagnosing astigmatism, as well as difficulties in diagnosing this condition in children. In Europe, the prevalence rate of astigmatism of 0.5 D or more in children is 12.9%, and in adults 39.7–67.97%. Overall, the prevalence rate of astigmatism greater than 0.5 D is 32.2–67.97%, greater than 1.0 D is 15.6–22.5%, greater than 2.0 D is 4.2–5.4%, and greater than 3.0 D is 1.6% [11,13].

1.4 Features of Coding the Disease or Condition

H52.2 – Astigmatism

1.5 Classification of the disease or condition

The generally accepted classification of astigmatism is supported by the majority of vision care specialists [1,2,3,4,5,6,10,14].

According to the combination of refractions in the principal meridians (the position of the focal lines of Sturm's conoid relative to the retina), 5 types of astigmatism are distinguished:

• Compound hyperopic;

• Simple hyperopic;

• Mixed;

• Simple myopic;

• Compound myopic.

According to the relative position of the principal meridians, 3 types of astigmatism are distinguished:

• With-the-rule – the meridian with stronger refraction is vertical or located within a ±30° sector from the vertical;

• Against-the-rule – the meridian with stronger refraction is horizontal or located within a ±30° sector from the horizontal;

• Oblique – both meridians lie in the sectors from 30° to 50° and from 120° to 150°.

• Based on the difference in the magnitude of astigmatism and the direction of the principal meridians, astigmatism is classified as:

• Isometropic;

• Anisometropic.

Based on the regularity of refraction within the meridian of astigmatism, astigmatism is classified as:

• Regular;

• Irregular*.

*These clinical guidelines consider only regular astigmatism

Astigmatism is classified into:

• Total (or refractive)

• Corneal;

• Internal (specifically distinguished by some authors [15,16], defined as the difference between total and corneal astigmatism).

The degree of astigmatism is determined by the difference in refraction between the weak and strong meridians, is expressed in diopters (D), and has no sign.

1.6 Clinical presentation of the disease or condition

Patient complaints include decreased distance and near visual acuity, distortion of the perceived space, monocular diplopia or polyopia, focusing difficulties, asthenopia, headaches associated with visual load, and decreased distance vision in the dark.

Objective refraction testing reveals astigmatism.

Visual acuity testing reveals a decrease in uncorrected visual acuity; depending on the type and form of astigmatism, the patient may correctly identify only horizontally or vertically oriented optotypes while incorrectly identifying others. Placing spherical lenses before the eye may slightly improve visual acuity, but it is always lower than the visual acuity achieved with astigmatic correction (a cylindrical lens or a combination of spherical and cylindrical lenses). When a cylindrical lens or a combination of spherical and cylindrical lenses is placed before the eye, visual acuity increases to 1.0 or higher. In cases where astigmatic correction does not improve visual acuity to normal values, it is referred to as refractive amblyopia induced by astigmatism.

In the majority of patients with astigmatism, binocular functions are preserved. No changes in the anterior segment of the eye are detected. Media are clear. No specific fundus changes are found.

2. Diagnostics, medical indications and contraindications for diagnostic methods

Criteria for diagnosing astigmatism: astigmatism values of 0.75 D and more, and cases where, with lower astigmatism values, correction with a cylinder improves visual acuity compared to any sphere.

2.1 Complaints and Anamnesis

Comments: when evaluating the history of the present illness, special attention should be paid to the age at which astigmatic correction was first prescribed and the date of the last prescription. The previous correction should be evaluated using a lensmeter. The dynamics of refraction and the astigmatic component should be assessed based on previous examination data or previously dispensed correction (spectacles). Assessing refractive dynamics based on the patient's subjective report in astigmatism has low informational value. When evaluating the personal and medical history, special attention should be paid to the characteristics and conditions of the patient's visual activity, the patient's expectations, and the availability of correction.

2.2 Physical Examination

Physical examination is not performed for astigmatism.

2.3 Laboratory Diagnostics

Laboratory diagnostic tests are not performed for astigmatism.

2.4 Instrumental Diagnostics

Comments: in children under three years of age, visometry is performed approximately – by determining whether the child has object vision. More precise measurement is possible using the preferential looking test, optokinetic nystagmus recording methods, and visual evoked potentials.

Visometry in children aged three years and older is performed using charts: from 3 years of age using a children's silhouette picture chart, from 5 years of age using Landolt rings or "E" tests. In adults, visual acuity is examined using Landolt rings or "E" tests. Examining visual acuity using letters and numbers in astigmatism is the least accurate method.

The value of visual acuity is taken as the chart line in which all symbols are correctly identified.

Comments: objective examination is performed using autorefractometers and/or skiascopy. In children, the examination is performed under natural conditions and after cycloplegia. In adults, the examination can be performed under natural conditions alone; cycloplegia is resorted to when examination under natural conditions yields ambiguous results.

Subjective refraction testing is performed in children older than three years and in adults. A cylindrical lens or a combination of a spherical and a cylindrical lens that achieves maximum visual acuity is selected.

Comments: automated refacto- and keratorefractometry is a reliable method for diagnosing astigmatism. The method allows for fast and accurate examination of astigmatism in adults and children older than three years under both narrow and wide pupils. In children older than one year, the examination is possible using a handheld modification of the autorefractometer; in children under 1 year of age, a pediatric remote autorefractometer can be used. The latter yields the least accurate results. Autorefractometry data do not constitute a ready-to-use prescription for spectacles or contact lenses – refinement using subjective methods is required [17,18]. The latter does not apply to infants and toddlers.

Comments: the method is of adjunctive importance in evaluating total ocular astigmatism. Although corneal and total ocular astigmatism values frequently do not coincide and there is no rigid correlation between these parameters, the following rule can be applied: if keratometry reveals direct corneal astigmatism up to 1.0 D, cylindrical correction is generally not required. With direct corneal astigmatism of 1.25 D and higher, as well as with inverse and oblique corneal astigmatism of any magnitude, astigmatism correction will be required with a high degree of probability [1].

Comments: skiascopy (retinoscopy) using a handheld mirror ophthalmoscope with a flat mirror or using an electric ophthalmoscope is a reliable method for assessing refraction, but has low accuracy in diagnosing astigmatism, particularly its principal meridians. More accurate results are provided by modified skiascopy techniques: cylinder skiascopy and streak skiascopy. In foreign literature, these methods are generally referred to as retinoscopy [4,14,19].

Comments: computer video keratotopography is a non-invasive diagnostic method that allows qualitative and quantitative analysis of the anterior corneal surface topography. The method is based on computer processing of Placido disc concentric rings projected onto the cornea, any distortion of which is recorded for computer analysis. The result can be obtained both in numerical values and as color-coded maps. It is recommended to perform 5 to 10 consecutive measurements to obtain the most accurate data. Tear film structure abnormalities can significantly affect the examination results.

Comments: Scheimpflug principle-based ophthalmic keratotopographic systems allow the measurement of both anterior and posterior corneal curvature, which is important for diagnosing and assessing the progression of primary and secondary corneal ectasias.

Comments: crossed-cylinder tests are performed under the best spherocylindrical correction that achieves the highest visual acuity; to obtain accurate astigmatic component values, it is necessary for the eye's retina to be positioned at the circle of least confusion, while the anterior and posterior focal lines lie in front of and behind the retina at an equal distance.

Axis test. The patient is asked to look at a line on the chart corresponding to a visual acuity level slightly above the threshold, or use the "multiple-dot test". The handle of the cross-cylinder is aligned with the axis of the correcting cylinder inserted in the trial frame, and the cross-cylinder is sequentially presented to the eye in two positions: first, the axis of the cross-cylinder with the same sign as the correcting cylinder is positioned to the right, and then to the left of the correcting cylinder's axis. If both positions of the cross-cylinder blur vision equally, the axis position of the correcting cylinder is correct. If there is a difference in vision between the two cross-cylinder positions, the correcting cylinder in the trial frame is rotated toward the similarly signed axis of the cross-cylinder in the position of best vision.

Power test. The handle of the cross-cylinder is positioned at a 45º angle to the axis of the correcting cylinder so that initially the axis of the correcting cylinder in the frame coincides with the similarly signed axis of the cross-cylinder. Then, the cross-cylinder is flipped so that the axis of the correcting cylinder coincides with the oppositely signed axis of the cross-cylinder. Depending on the patient's responses, the power of the correcting cylinder is increased, decreased, or left unchanged.

The power of the spherical component of the correction is refined if the power of the correcting cylinder has been changed by 0.5 D or more. Thus, an increase in minus cylinder power by 0.5 D requires a decrease in minus sphere or an increase in plus sphere by 0.25 D. Cross-cylinder tests can be used in children over 8 years of age in 53.6±5.6% of cases, in children over 11 years of age in 73.7±7.4% of cases, and in adults in 73.3±9.2% of cases. When subjects do not understand the testing instructions, objective measurement data are taken as the basis.

Comments: the examination using a stenopeic slit involves placing the stenopeic slit alternately before the eye in two principal meridians and selecting the best spherical lens for each of them. This method has low diagnostic value and can only be used as a preliminary test.

Comments: the Snellen astigmatism chart is a board with radial lines drawn around the entire circumference every 10–30º. The use of the astigmatism chart helps answer whether the patient has astigmatism or not. If, under the best spherical correction, all lines of the chart appear equally clear to the patient, it is concluded that there is no astigmatism. If, against a background of slight blurring of most lines, two mutually opposite lines stand out as darker, the presence of astigmatism is concluded. To detect evenly mixed astigmatism, an examination is performed with a +0.5 D lens. The direction of the lines will indicate the approximate direction of one of the principal meridians of the astigmatic eye [30].

Comments: Scheimpflug-principle-based ophthalmologic keratotopographic systems allow the measurement of both anterior and posterior corneal curvature, which is important for diagnosing secondary astigmatism in keratoconus and after refractive surgeries.

2.5 Other Procedures

No other diagnostic tests are performed for astigmatism

3. Treatment, including drug and non-drug therapies, diet therapy, and pain management

3.1 Optical correction

Comments: astigmatism of less than 1.0 D may be self-compensated and often does not require optical correction. Correction is required when cylinder correction improves visual acuity compared to sphere alone, typically in cases of against-the-rule astigmatism and oblique astigmatism. Correction of with-the-rule astigmatism of less than 1.0 D is less frequently required, but possible. When the fellow eye has astigmatism requiring correction, low-magnitude astigmatism is also corrected, but only if cylinder correction does not reduce visual acuity.

Comments: in infants under one year of age, astigmatism correction is needed only as an exception. At up to three years of age, during the height of the emmetropization process, astigmatism greater than 2.0 D is corrected based on objective examination data, especially if accompanied by spherical ametropia. As a rule, partial astigmatism correction is prescribed, considering that astigmatism decreases in the majority of children by the age of three.

Comments: at three years of age and older, if subjective refraction testing is impossible, any type of astigmatism of 1.0 D or more is corrected. Astigmatism correction close to full correction is prescribed in accordance with objective data. When subjective testing becomes possible, it is decisive in prescribing correction. The sphere is corrected for the highest visual acuity. The cylinder is added in cases of refractive amblyopia and/or when it improves vision compared to any sphere. Typically, these are with-the-rule astigmatism of 1.0 D or more, or against-the-rule and oblique astigmatism of 0.5 D or more. The cylinder that yields the highest visual acuity is prescribed. The axis position and cylinder power are refined using crossed cylinders, if possible. Children under 12 years of age generally adapt easily to astigmatic spectacles of any complexity, even if astigmatic correction is prescribed for the first time. For children over 12 years of age, astigmatic correction is prescribed taking into account its tolerability, especially when astigmatic spectacles are prescribed for the first time.

Comments: as a rule, reducing the astigmatic correction leads to improved tolerability, especially for spectacles. However, such a reduction is always accompanied by a decrease in visual acuity. Therefore, when prescribing astigmatic correction (spectacles), one should aim for full correction, resorting to undercorrection of astigmatism only in cases of maladaptation. Following full adaptation to astigmatic spectacles, the astigmatism correction should be increased to full; this is usually possible after 3–6 months of wearing the correction (spectacles).

Comments: in bifocal and progressive spectacles, as well as in occupational spectacles with degression, identical values of the astigmatic component are already incorporated into the lens design, so specifying only the addition is sufficient for near vision.

3.2 Contact lens correction

Comments: the advantage of contact lenses over spectacles is the creation of a sharper image on the retina, reduction of aberrations, absence of prismatic effect, and absence of visual field restriction by the spectacle frame [1, 27].

Comments: in the presence of relative contraindications to contact lens wear, astigmatism correction with contact lenses should be approached with caution, carefully selecting the type of contact lenses, their wear schedule, and follow-up intervals.

Comments: when fitting custom-designed soft toric contact lenses (STCLs), rigid gas-permeable contact lenses (RGCLs), scleral gas-permeable contact lenses (SGCLs), and orthokeratology contact lenses (OKLs) in children, the recommended follow-up interval may be shortened to 3 months.

Comments: mass-produced soft toric contact lenses imply scheduled monthly, bi-weekly, or daily replacement. The lenses are manufactured from hydrogel or silicone hydrogel materials and offer a high level of comfort. The minimum astigmatic component values for STCLs are 0.75 D, maximum values are 2.75 D, with a 0.5 D step. Lens refraction is indicated in the prescription format SPH-CYL-AX, where cylinder values are always negative, the spherical component ranges from +6.0 D to -10.0 D, and the cylinder axis step is 10°. Mass-produced STCLs can be fitted to patients with a corneal diameter from 12.0 to 9.5 mm and a corneal radius of curvature from 7.4 mm to 8.2 mm. It is preferable to prescribe daily disposable STCLs for children, though it should be kept in mind that the maximum cylinder values in such lenses are 2.25 D. Fitting soft spherical contact lenses or STCLs in combination with astigmatic spectacles prescribed over the contact lenses is permissible. This allows correction of astigmatism exceeding 3.0 D using soft contact lenses.

Comments: custom STCLs are prescribed in cases where there is no compliance with corneal parameters or the degree of refraction achievable with standard scheduled-replacement STCLs. Such lenses are fitted by an ophthalmologist with appropriate training. Custom STCLs are manufactured by lathe-cutting hydrogel and silicone hydrogel materials and can have an optical power ranging from +30.0 D to -30.0 D with a cylinder of up to 10.0 D. The service life of custom lenses ranges from 3 to 6 months. Prescribing custom STCLs for astigmatism up to 1.5 D should be avoided, as visual acuity may turn out to be lower than with spectacles. In patients with astigmatism and presbyopia, multifocal design STCLs can be fitted and manufactured [27].

Comments: corneal gas-permeable contact lenses (RGCLs) are a self-supporting structure, which ensures the formation of an "optically active" sub-lens tear film portion. RGCLs can be spherical, back-toric, front-toric, and bi-toric (both front and back surfaces are toric). RGCLs are made from a gas-permeable material with an oxygen permeability (Dk) of at least 50. The diameter of RGCLs is smaller than the horizontal diameter of the cornea. RGCLs are custom-manufactured in a laboratory according to an ophthalmologist's prescription. The choice of RGCL type depends on the type of astigmatism and the shape of the corneal surface. Spherical RGCLs compensate for corneal astigmatism up to 3.0 D for any degree of ametropia. Back-toric RGCLs are prescribed for corneal astigmatism of 3.0 D and greater. Front-toric RGCLs are prescribed for lenticular astigmatism, and bi-toric lenses for corneo-lenticular astigmatism. RGCLs do not contact the limbal zone and bulbar conjunctiva of the eyes, so they can be prescribed to patients with disorders in these areas. RGCLs do not contain liquid, do not affect tear exchange, and can be fitted for astigmatism correction in combination with dry eye syndrome [27].

Comments: scleral gas-permeable contact lenses (SGPCL) are self-supporting structures that do not contact the anterior surface of the cornea or the limbal zone and rest on the bulbar conjunctiva 1–2 mm from the limbus. SGPCLs can be miniscleral (diameter less than 16 mm) and scleral (diameter 16 mm and more). Miniscleral lenses are preferred for the correction of regular astigmatism. SGPCLs are made of gas-permeable material with an oxygen permeability of at least 125 Dk. As a rule, all SGPCLs are custom-made according to an ophthalmologist's prescription. The choice of SGPCL type depends on the type of astigmatism and the shape of the anterior surface of the eye. SGPCLs can be spherical or front-toric. Spherical SGPCLs are prescribed only for corneal astigmatism, while front-toric ones are prescribed for both corneal and total astigmatism. Spherical SGPCLs successfully compensate for regular corneal astigmatism of any degree and irregular astigmatism. SGPCLs contain no liquid, do not affect tear exchange, and can be fitted for astigmatism correction in combination with dry eye disease when other types of contact lenses cannot be used. In children, SGPCLs are prescribed for corneal astigmatism of .0 diopters or more at the age of two years and older. In patients with astigmatism and presbyopia, fitting multifocal design SGPCLs is possible.

Comments: orthokeratology contact lenses (OKLs) are reverse-geometry corneal gas-permeable contact lenses intended for the temporary modification of the shape and optical power of the cornea. OKLs are made of highly gas-permeable materials with an oxygen permeability of at least Dk 100. The refractive effect is associated with a change in epithelial thickness in the center and mid-peripheral zone of the cornea due to changes in the shape and size of superficial epithelial cells [56,57]. OKLs are worn at night (during sleep). During the day, the patient does not use any vision correction aids. Individual toric OKLs are prescribed for corneal astigmatism up to 5.0 diopters. OKLs for astigmatism correction are custom-manufactured in a laboratory according to an ophthalmologist's prescription, who designs the lens using special computer programs.

3.3 Surgical correction

Comments: in adults, surgical correction of astigmatism is resorted to if the patient prefers surgical correction over other methods of astigmatism correction (glasses or contact lenses). Excimer laser photorefractive keratectomy—excimer laser correction of regular astigmatism—is performed for astigmatism up to 6.0 diopters [60,61,62]. Excimer laser correction in the form of LASIK, FemtoLASIK, PRK, and SMILE is currently the most popular standalone method for correcting regular astigmatism. Modern lasers are capable of correcting astigmatism up to 6.0 diopters in the absence of contraindications to the excimer laser correction method. Excimer laser correction of hyperopia and hyperopic astigmatism, in particular, is inferior in the stability and efficacy of its results compared to the same procedure for myopia and myopic astigmatism. During cataract surgery or clear lens extraction with intraocular lens (IOL) implantation in corneal astigmatism from 0.5 to 2.5 diopters, tangential keratotomy or limbal relaxing incisions (LRIs) are used to achieve high uncorrected visual acuity after surgery [63,64,65]. To correct high refractive errors and achieve high uncorrected visual acuity postoperatively, phakic toric IOL implantation is used in adult patients with astigmatism and ametropia greater than 8.0 diopters who prefer surgical correction of refractive errors, and in cases where other correction methods are inapplicable or yield significantly inferior refractive and functional outcomes [66,67]. This method allows for the correction of astigmatism up to 6.0 diopters. For higher degrees of astigmatism, bioptics (a combination of phakic IOL implantation with excimer laser correction) or custom-made phakic IOLs can be used. In adult patients with astigmatism undergoing cataract removal and refractive lens exchange, phacoemulsification with toric intraocular lens implantation is performed [68,69,70].

3.4 Functional treatment

Comments: in most cases of astigmatism, wearing an astigmatic correction corresponding to the refraction increases the corrected visual acuity to 1.0 or higher within the first 3 months of wear.

Medical treatment is not carried out.

Medical nutrition therapy is not prescribed.

4. Medical Rehabilitation and Sanatorium-Resort Treatment

Sanatorium-resort treatment and the use of medical rehabilitation methods based on natural therapeutic factors are not required (data on their efficacy, indications, and contraindications are lacking).

5. Prevention and Dispensary Observation

6. Organization of Medical Care

Medical care for astigmatism is provided on a scheduled basis.

Primary pre-medical healthcare for astigmatism is provided by mid-level medical personnel; primary physician-led healthcare for astigmatism is provided by district pediatricians and general practitioners (family physicians). Upon suspicion or detection of signs of decreased visual acuity, including signs of astigmatism, mid-level medical personnel, district pediatricians, and general practitioners (family physicians) refer patients for a consultation with an ophthalmologist. Primary specialized healthcare for astigmatism is provided by an ophthalmologist.

In accordance with Order of the Russian Ministry of Health No. 514n dated August 10, 2017, "On the procedure for preventive medical examinations of minors" (as amended by Orders of the Russian Ministry of Health No. 410n dated July 3, 2018, No. 396n dated June 13, 2019, and No. 1235n dated November 19, 2020), during preventive medical examinations of minors, including upon admission to educational institutions and during the period of study, an ophthalmologist examines children at the ages of 1 month, 12 months, 3 years, 6 years, 7 years, 10 years, 13 years, 15 years, 16 years, and 17 years.

Adults with astigmatism are examined by an ophthalmologist during preliminary and periodic medical examinations upon employment and throughout employment in accordance with departmental regulatory acts and/or in accordance with Order of the Ministry of Labor No. 988n and the Russian Ministry of Health No. 1420n dated December 31, 2020, "On approval of the list of harmful and (or) hazardous production factors and jobs in the performance of which mandatory preliminary medical examinations upon admission to employment and periodic medical examinations are carried out," and Order of the Russian Ministry of Health No. 29n dated January 28, 2021, "On approval of the procedure for conducting mandatory preliminary and periodic medical examinations of workers provided for by Part Four of Article 213 of the Labor Code of the Russian Federation, the list of medical contraindications to the performance of work with harmful and (or) hazardous production factors, as well as work in the performance of which mandatory preliminary and periodic medical examinations are carried out."

Astigmatism is also detected when children and adults actively seek care at the ophthalmology office in the serviced area with complaints of decreased vision.

The ophthalmologist of the ophthalmology office provides: consultative, diagnostic, and therapeutic care; in the presence of medical indications, refers children to the pediatric vision conservation room or the pediatric ophthalmology department.

Medical care for children with amblyopia induced by astigmatism may (if outpatient treatment is not feasible) be provided in a day or inpatient setting (at the discretion of the head of the pediatric ophthalmology department).

The indication for hospitalization in a medical organization is amblyopia in children induced by astigmatism. Children are referred to a day or 24-hour inpatient facility for pleoptic treatment if it cannot be performed on an outpatient basis.

The indication for discharging a patient from a medical organization is the complete completion of the planned course of treatment.

7. Additional Information

Astigmatism management involves two main tasks: first, the most accurate diagnosis of astigmatism; second, the selection of its optimal correction. The best method for diagnosing astigmatism is automatic refractometry, which allows for fast and accurate examination of astigmatism in adults and children over three years of age with both narrow and wide pupils. In children under three years of age, handheld modifications of autorefractometers, including specialized pediatric ones, or skiagraphy (retinoscopy) are used. Skiascopy using a flat mirror of a hand-held ophthalmoscope is the crudest method for diagnosing astigmatism, with errors reaching 1.5–2.0 D, and the direction of the principal meridians can be determined only very approximately. A definitive conclusion regarding astigmatism should be made only after thorough subjective testing: power and axis determination. When choosing astigmatic correction, the following are taken into account: the magnitude of astigmatism, the type of astigmatism, the type and degree of concomitant ametropia, age, the feasibility and results of subjective testing, previous correction, tolerance of astigmatic correction, and the nature of visual load [1,2,6,36].

Criteria for Evaluating the Quality of Medical Care

References

Appendix A1. Working Group Composition

1. Myagkov Alexander Vladimirovich, MD, Professor, Association of Ophthalmologists LLC;

2. Pershin Kirill Borisovich, MD, Professor, Association of Ophthalmologists LLC;

3. Proskurina Olga Vladimirovna, Dr. of Med. Sci., Association of Ophthalmologists LLC;

4. Tarutta Elena Petrovna, Group Head, MD, Professor, Association of Ophthalmologists LLC;

5. Khodzhabekyan Narine Vladimirovna, PhD in Medicine, Association of Ophthalmologists LLC

No conflict of interest is declared.

Appendix A2. Methodology for Developing Clinical Guidelines

Methods used for collecting/selecting evidence: searching electronic databases; analysis of modern scientific developments on the problem of astigmatism in Russia and abroad; synthesis of practical experience of Russian and foreign colleagues.

When selecting publications as potential sources of evidence, the methodology used in each study is examined to ensure its reliability. The result of this examination affects the level of evidence assigned to the publication, which in turn affects the strength of the recommendations derived from it.

A preliminary version of these guidelines was reviewed by independent experts who were asked to comment primarily on whether the interpretation of the evidence underlying the recommendations is reliable and accessible to practicing physicians and patients.

Feedback has been received from ophthalmologists specializing in myopia and primary care physicians regarding the clarity of presentation and the importance of the recommendations as a practical tool for everyday medical practice.

Comments received from experts were thoroughly systematized and discussed by the working group chairs and members. Each item was discussed. Changes and additions recommended as a result of the discussion were incorporated into the text of the recommendations.

Target audience for these clinical guidelines:

1. Ophthalmologists;

2. General practitioners (family physicians);

3. Pediatricians;

4. Urban (district) pediatricians;

5. District pediatricians;

6. Medical optics optometrists.

Table 1. Level of Evidence (LoE) grading scale for diagnostic methods (diagnostic interventions)

Table 2. Scale for assessing levels of reliable evidence (LRE) for prevention, treatment, and rehabilitation methods (preventive, therapeutic, rehabilitation interventions)

Table 3. Grade of Recommendation (GoR) scale for prevention, diagnostic, treatment, and rehabilitation methods (preventive, diagnostic, therapeutic, and rehabilitative interventions)

Procedure for updating clinical guidelines.

The mechanism for updating clinical guidelines provides for their systematic revision at least once every three years, as well as upon the emergence of new evidence-based medicine data on the diagnosis, treatment, prevention, and rehabilitation of specific diseases, or in the presence of justified additions/comments to previously approved clinical guidelines, but no more frequently than once every 6 months.

Appendix A3. Reference Materials

These clinical guidelines were developed taking into account the following regulatory legal documents:

1. Order of the Russian Ministry of Health No. 442n dated October 25, 2012, "On Approval of the Procedure for Providing Medical Care to Children with Diseases of the Eye, Its Adnexa, and Orbit."

2. Order of the Russian Ministry of Health No. 902n dated November 12, 2012, "On Approval of the Procedure for Providing Medical Care to Adults with Diseases of the Eye, Its Adnexa, and Orbit" (as amended)

3. Order of the Russian Ministry of Health No. 45n dated February 2, 2022, "On Approval of the Standard of Medical Care for Adults with Astigmatism (Diagnosis, Treatment, and Dispensary Observation)"

4. Order of the Russian Ministry of Health No. 969n dated October 6, 2021, "On Approval of the Standard of Medical Care for Children with Astigmatism (Diagnosis, Treatment, and Dispensary Observation)"

5. Order of the Russian Ministry of Health No. 203n dated May 10, 2017, "On Approval of Criteria for Assessing the Quality of Medical Care"

6. Order of the Russian Ministry of Health No. 514n dated August 10, 2017, "On the Procedure for Conducting Preventive Medical Examinations of Minors" (as amended by Orders of the Russian Ministry of Health No. 410n dated July 3, 2018, No. 396n dated June 13, 2019, No. 1235n dated November 19, 2020)

7. Order of the Ministry of Labor No. 988n and the Russian Ministry of Health No. 1420n dated December 31, 2020, "On Approval of the List of Harmful and (or) Hazardous Production Factors and Jobs in Performing Which Mandatory Preliminary Medical Examinations upon Employment and Periodic Medical Examinations Are Carried Out"

8. Order of the Ministry of Health of the Russian Federation dated January 28, 2021, No. 29n "On approval of the procedure for conducting mandatory preliminary and periodic medical examinations of workers provided for by part four of article 213 of the Labor Code of the Russian Federation, the list of medical contraindications to carrying out work with harmful and (or) hazardous production factors, as well as jobs upon performance of which mandatory preliminary and periodic medical examinations are carried out."

Appendix B. Physician Action Algorithms

Appendix C. Patient Information

Astigmatism (from the Greek *a-* meaning negation and *stigma* meaning point) is not an eye disease, but rather a structural feature of the optical apparatus of the eye. An eye with astigmatism refracts light rays differently in two mutually perpendicular meridians, forming a blurred image in the form of a line, oval, or circle on the retina instead of a sharp point image like a person with normal vision.

Astigmatism is most often a congenital condition and is detected in almost all people, but in most of them, it is insignificant and does not interfere with normal vision. Such astigmatism is called physiological, and correction is not prescribed for it. In some people, astigmatism turns out to be higher than physiological values. Such astigmatism significantly affects vision—reducing visual acuity for distance and near, and impairing visual performance at all distances. Such astigmatism should be corrected.

Glasses are most commonly used to correct astigmatism. In recent years, contact lenses have been used to correct astigmatism. Modern developments in refractive surgery technology allow astigmatism to be corrected surgically and are used in cases where a person with astigmatism does not wish to wear glasses or contact lenses and prefers to undergo surgical correction of astigmatism.

Regardless of the method of astigmatic correction, if the correction is selected correctly, the patient has high visual acuity for both distance and near, good visual performance, and the prescribed correction is comfortable and causes no discomfort. Properly selected astigmatism correction in children helps improve visual acuity, promotes proper eye development, and serves as prevention for the development and progression of myopia. In adults, in addition to ensuring high visual quality, astigmatic correction prevents the development of visual fatigue.

For children with astigmatism, correction is always prescribed for continuous wear. In adults, the wearing regimen for astigmatic correction may be less strict, but continuous wear is preferable.

The opinion that prescribing correction for astigmatism worsens vision is erroneous and has no basis whatsoever.

If astigmatic correction is refused in children, persistent amblyopia (reduced vision) may develop, which, without timely correction and treatment, may become lifelong and significantly impair quality of life in adulthood, hinder education, influence career choice, and impose other limitations.

If an adult refuses astigmatic correction, their distance and near visual acuity and visual performance will be reduced.

If astigmatism is detected in a child, ophthalmological monitoring is required at least once a year. An adult with astigmatism requires monitoring every 2–3 years. Remember to bring your previous glasses and/or prescription for glasses (contact lenses) and/or records of previous examinations to every follow-up visit with the ophthalmologist.

Appendix G. Assessment Scales, Questionnaires, and Other Evaluation Tools

Not used