Ortho-k lenses

The inhibitory effect of progressive myopia, confirmed by studies around the world, makes orthokeratology especially attractive for pediatric and adolescent ophthalmology practice, a tool of choice for progressive myopia. The medical, social and economic significance of this fact cannot be overestimated.
Orthokeratology is an officially recognized method of inhibiting the progression of myopia in children. Since 2013, orthokeratology has been included in the “Federal Clinical Guidelines for the Diagnosis and Treatment of Myopia in Children”
Since myopia is the most common optical defect requiring correction and one of the most significant medical and social problems, it is important to determine the place of this method in the complex of therapeutic and preventive measures.

Mechanism of action

It has been proven that the change in the curvature of the outer surface of the cornea and, consequently, the change in the refraction of the eye under the influence of OCL occurs due to changes in the architectonics of the corneal epithelium. It is the epithelium that is influenced by the hydrodynamic forces that arise in the lacrimal layer under the OCL. The result is a flattening of the epithelium in the central zone and its thickening in the middle periphery of the cornea. Epithelial changes occur at the micron level. These changes are not accidental but are programmed with a special geometry of the rear surface of the lens to achieve the required refractive effect. OCL design largely determines the nature of the observed changes.
At the histological level, changes in the shape and size of cells in the surface layers of the epithelium are observed, while the number of epithelial layers remains the same. Fundamentally important is the fact that the size of the cells of the basal layer, providing regeneration of the epithelium, do not change. The absence of changes in the structure of desmosomes, microvilli and micro-folds of epithelial cells was shown. The integrity and normal permeability of the epithelium are preserved. Bowman’s membrane, stroma and corneal endothelium also do not show changes that affect the functional characteristics of the cornea. It was found that the use of OCL does not have a negative effect on the cytoarchitectonics of corneal cells does not lead to clinically significant anatomical and functional disorders. During the follow-up period from 2 to 7 years, no increase in corneal changes is observed, and even their decrease is noted, which may indicate the adaptation of corneal tissues to OCL. Thinning of the cornea does not occur. OK-therapy also does not lead to a significant change in the curvature of the posterior surface of the cornea.
The priority of the longest (14 years) systematic scientific research on the use of OCL belongs to the specialists of the Federal State Budgetary Institution “Moscow Research Institute of GB im. Helmholtz “Ministry of Health of Russia, Department of refraction pathology, binocular vision and ophthalmoergonomics.

Indications and contraindications

When referring patients to the fitting of orthokeratological lenses to achieve high functional results and prevent complications, patient selection must be carried out very carefully. The ophthalmologist must take into account the following indications and contraindications:

Indications

Progressive myopia; myopia; myopic astigmatism; hypermetropia; presbyopia; inability to use glasses and contact lenses during active hours of the day for professional reasons (athletes, drivers, workers in smoky or dusty rooms using aerosols, etc.) or for other reasons; inability to perform laser surgery; dry eye symptoms when wearing soft contact lenses. (Child’s age – from 6 years old. Adults – no age limit; after 40 years, when choosing lenses, you will need to take into account the features associated with the appearance of presbyopia, as well as with changes in tear production).

Criteria for keratometry and corneal refraction *

Corneal keratometry index from 37.50 to 50.00 D; myopia from 0.25 to 8.00 D in terms of spheroequivalent (with higher myopia, incomplete correction is possible if the patient agrees that he will have residual myopia); corneal astigmatism up to 5.00 D, myopia value no more than 8.00 D. Hyperopia up to 4.00 D.

* Criteria are indicated for lenses of DL-ESA design (Doctor Linz Techno, Russia). Criteria may differ for other OK lens designs and other restrictions may apply.

Contraindications

Absolute

Inflammatory diseases of the eye, adnexa and orbit, history of keratitis; pronounced dry eye (xerosis); dystrophic diseases of the cornea (keratoconus, keratoglobus, pellucid marginal degeneration); pronounced nystagmus; lagophthalmos; single eye; severe immunodeficiency states of any etiology; acute infectious and inflammatory diseases; collagenoses; malignant neoplasms of the eye and its auxiliary apparatus; a significant decrease in the sensitivity of the cornea; taking isotretinoin drugs (during the course of administration); psychological features that prevent the safe use of OCL.

Relative

Wide pupil; irregular astigmatism; opacity and scarring of the cornea; radiation therapy and chemotherapy until treatment is complete; dry eyes caused by unfavorable environmental conditions, taking medications, the specifics of work; violation of the composition of the tear; condition after LASIK; pregnancy, lactation period; endocrine diseases; autoimmune diseases; oncological diseases; seasonal allergies; the use of corticosteroid drugs.

The final decision on the possibility of selecting OCL for a particular patient is made by the doctor of a specialized office / clinic.

Safety

Orthokeratology is recognized as a safe medical technology.
With adequate selection and adherence to the rules of wearing and caring for orthokeratological lenses, their prolonged use does not lead to clinically significant complications.
It has been proven that there is no direct damaging effect on the cornea and conjunctiva of the eye, as well as on the volume and quality of tears, which confirms the safety of using OK lenses in children.
OK-therapy does not affect intraocular pressure and does not lead to a change in the curvature of the posterior surface of the cornea.
Against the background of orthokeratological correction, there was no negative effect of the method on the occurrence and progression of PWHM, as well as the dynamics of ocular blood flow.
However, non-compliance by the patient with the rules of wearing and care can lead to infectious complications.
The only serious complication of contact correction is microbial keratitis. The incidence of microbial keratitis with OC therapy is no more than 0.07–0.09% of cases per year. The safety of OK-therapy is within the limits accepted in the world clinical practice of contact vision correction.

The prevalence of myopia and its complications

In the modern world, the prevalence of myopia is high and continues to grow. Currently, more than 30% of the total population of Europe and North America and almost 50% of young people are nearsighted, of which more than 10% have high myopia. The prevalence of myopia among young people in Southeast Asia is approaching 90%.

In Russia, 35% are short-sighted among the adult population and up to 50% among graduates of gymnasiums and lyceums.

High myopia causes a noticeable decrease in the quality of life due to a lack of visual information and dependence on vision correction tools.

High myopia is fraught with serious complications, such as retinal detachment and myopic retinopathy, which leads to irreversible changes in the central parts of the retina and a significant decrease in visual acuity, up to complete blindness. The incidence of retinal detachment in patients with myopia less than 3 diopters occurs 4 times more often than in those with emmetropia, and in patients with high myopia 10 times more often.

Complications of myopia occupy a key position in the list of causes of visual disability. Myopia is usually bilateral and affects people early in their productive years. The duration of blindness caused by myopic maculopathy is record-breaking (17 years). For comparison: with glaucoma – 10 years, diabetes mellitus and age-related macular degeneration – 5 years.

Inhibition of myopia

For a number of years, doctors and optometrists who actively practice OK therapy have reported that children develop myopia more slowly when wearing OKL than their peers who wore glasses, soft or hard day contact lenses. At first, these data were ignored, since it was believed that the effect is associated with changes in the cornea, and not with a slowdown in the growth of the axial length of the eye.
The results of studies carried out in various countries (see table and recently published meta-analysis data have convincingly proved that orthokeratology inhibits the true progression of myopia, i.e. significantly slows down the increase in the axial length of the eye. According to the Moscow Research Institute of Eye Diseases. Helmholtz, the use of OCL leads to inhibition of the progression of myopia in 80.4% of cases.

Table. Influence of OK-therapy on changes in the axial length of the eye and refraction
in patients with progressive myopia

 

Study Wearing period ∆ parameter (OK) ∆ parameter (control) ∆ PZO K / ∆ PZO OK
Cheung, Cho, Fan (2004) 3 years 0.04 mm per year 0.11 mm per year 2.6 (up 62%)
LORIC (2005) 2 years 0.15 mm per year 0.27 mm per year 1.8 (up 44%)
CRAYON (2009) 2 years 0.13 mm per year 0.29 mm per year 2.2 (up 55%)
Kakita et al. (2011) 2 years 0.20 mm per year 0.31 mm per year 1.6 (up 35%)
Hiraoka et al. (2012) 5 years 0.20 mm per year 0.28 mm per year 1.4 (up 29%)
MCOS (2012) 2 years 0.24 mm per year 0.35 mm per year 1.5 (up 31%)
ROMIO (2012) 2 years 0.18 mm per year 0.32 mm per year 1.8 (up 44%)
TO-SEE (2013) 2 years 0.16 mm per year 0.32 mm per year 2.0 (up to 50%)
Cheung & Cho (2013) 0.5 years 0.20 mm per year 0.40 mm per year 2.0 (up to 50%)
Charm & Cho (2013) 2 years 0.10 mm per year 0.26 mm per year 2.6 (up 62%)
SMART (2015) 3 years -0.04 D per year -0.34 D per year 7.9 (up 87%)
Swarbrick et al. (2015) 1 year 0 mm per year 0.13 mm per year – (100%)
Verzhanskaya, Tarutta, Mirsayafov (2005) 2 years 0.10 mm per year ——— ———
Toloraya (2010) 7 years 0.07 mm per year ——— ———
Nagorsky (2014) 5 years 0.12 mm per year 0.28 mm per year 2.33 (up 57%)
Nagorsky (2014) 5 years -0.29 D per year -0.72 D per year 2.48 (up 60%)
Verzhanskaya (2017) 10 years 0.09 mm per year 0.29 mm per year 3.2 (up 69%)

 

Experimental evidence has been obtained that the effective inhibition of the progression of myopia during OC therapy is based on a change in the nature of peripheral refraction