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Associations of high myopia in childhood.

1 CET POINT

This article considers the disorders that may be identified in children presenting with myopia in childhood. An overview of the ocular features of these conditions is discussed along with the systemic findings where appropriate.

INTRODUCTION

High myopia can often occur as a precursor to, concurrent with, or subsequent to ocular disorders, systemic diseases and hereditary syndromes. The recognition of these cases is imperative as there is a risk of visual loss from sight-threatening complications. Regardless of this, there is currently no standardised provision for the screening, referral or examination of children presenting with high levels of myopia in the United Kingdom.

BACKGROUND

It is clear that myopia is not always an entirely benign, purely refractive, condition. The potential degenerative consequences of high myopia are also of concern. A strong link has been made between myopia and degenerative changes including retinal detachment, glaucoma, myopic maculopathy and chorioretinal changes. (1) Although any level of myopia has the potential to precipitate degeneration, (2) those with refractive errors over 6.00D are most susceptible (see Figures 1 and 2, page 48). (2,3)

In 75% of cases, myopia first occurs at around nine to 10 years of age and results in an adult refraction of approximately 2.00-5.00D. Generally, the earlier myopia manifests, the quicker the progression, and the higher the degree of eventual refractive error. The vast majority of congenital or early onset myopias reach over

6.00D.

A study examining all children presenting to two ophthalmology departments over three years found only 8% of high myopias to be 'simple high myopia'--that is myopia associated with no ocular or systemic morbidity. (4) This figure rises to 56% in a study looking at children presenting to their community optometrist or orthoptist with more than 5.00D of myopia. (5) It is clear that high myopia is associated with a high prevalence of ocular and systemic abnormalities in young children. Myopia may be the presenting feature, hence optometrists should be particularly aware of the potential differential diagnoses of high myopic error in childhood, know how to manage these patients and refer when appropriate.

ISOLATED HIGH MYOPIA

Progressive myopia can occur in the absence of recognised predisposing ocular or systemic disease, often resulting in errors of 10.00-15.00D in early childhood. Such cases should be referred to an ophthalmologist and investigated for occult collagenopathy, in addition to the rest of the conditions discussed below.

DEPRIVATION MYOPIA

Studies of amblyopia in the 1970s discovered that inducing visual deprivation by suturing the eyelids of new-born animals induces axial myopia. (6,7) Later experiments showed that exposure to anomalous patterned stimuli through corneal opacification, (8) and the use of pattern vision attenuating occluders, (9) induced a myopic shift. These experiments established the important regulatory role of visual experience in eye growth in animals and humans. Research has also shown that good visual experience is required for emmetropisation to occur; that is, the reduction in refractive power in early childhood towards a more emmetropic refractive state.

Rabin et al investigated emmetropisation in humans by studying ocular conditions known to disrupt pattern vision in early life. (10) There was a significant increase in the incidence of myopia in subjects with ocular anomalies, regardless of the underlying pathology or which part of the visual axis was affected.

Although it is possible that there is an innate disease process in all of these disparate conditions which cause myopia, it seems more reasonable to suggest that regardless of the cause of disturbance to form vision, prolonged exposure to pattern blur in early childhood can induce myopia by disrupting emmetropisation. It also supports the theory of a focus-sensor in the retina that transmits to the sclera to induce scleral remodelling.

The mechanism behind the genesis of refractive errors is unknown, though in recent years it has been postulated that the state of image focus on the retinal periphery may be more significant than central retinal image quality. Clinical observations of patients who have peripheral retinal abnormalities provide support for the idea that visual signals from the peripheral retina can have a significant impact on emmetropisation at the fovea and possibly the development of refractive errors. These patients frequently have higher refractive errors as well as exhibiting a larger than normal range of refractive error than children with eye diseases that primarily affect central vision. (10-14)

OCULAR ASSOCIATIONS Retinal dystrophies

Several retinal dystrophies can be associated with myopia. (4) The precise mechanism of development of myopia is not understood. The retinal dystrophy can be stationary, as in congenital stationary night blindness, or progressive with conditions such as cone-rod dystrophy, retinitis pigmentosa (see Figure 3, page 49), Bardet Biedl syndrome and other ciliopathies.

Keratoconus

Keratoconus is a progressive, non-inflammatory, bilateral, often asymmetric corneal disease, characterised by stromal weakening leading to corneal ectasia; this results in visual loss from progressive irregular astigmatism and myopia, and corneal scarring.

[FIGURE 1 OMITTED]

Childhood cataracts

Children undergoing cataract extraction with IOL implantation at a young age can develop significant and unpredictable myopic shift despite adjusting the IOL power for the anticipated growth of the infant eye. It is believed to be due to interference with the process of emmetropisation, but the precise mechanism is not understood. (15)

[FIGURE 2 OMITTED]

Syndrome of unilateral high myopia with myelinated nerve fibres

Myelinated retinal nerve fibres are developmental anomalies, present in approximately 1% of all eyes. (16) The development of very high myopia and amblyopia is a common finding in eyes with peripapillary myelinated nerve fibres. Patients with this condition should receive corrective lenses for their myopia and astigmatism, and may benefit from occlusion therapy. (17)

SYSTEMIC CONNECTIVE TISSUE DISORDERS

Axial myopia is likely to be associated with changes in the component structural elements of the eye such as the sclera. Conditions with a known alteration in the connective tissue have been associated with high myopia. (18-20) Connective tissue disorders can affect any body structure resulting in a wide range of characteristic abnormalities. The severity of these syndromes varies widely from subtle features, to profound, or life-threatening complications.

The distinguishing physical features of some connective tissue disorders are enumerated in Table 1.

Marfan syndrome

Patients with collagenopathies such as Marfan syndrome can develop cardiac valve incompetence or present with sudden death or severe heart failure as a result of aortic dissection. Any suspicion of a connective tissue disorder should prompt a medical genetics or cardiac referral, as timely detection can potentially save or prolong life for these patients.

Abnormal connective tissue proteins cause Marfan syndrome. One in 5,000 people is affected by the condition. It is an autosomal dominant condition and there is a positive family history in three-quarters of cases. Patients with Marfan syndrome have a 50% chance of passing it on to their children. However, the condition can occur spontaneously without being inherited. Men and women, (21) from any ethnic group, (22) can be affected. Common ocular findings include:

* Bilateral ectopia lentis (in 50-80% of cases) (18)

* High myopia

* Lens opacities

* Glaucoma

Retinal detachment, associated with predisposing factors such as retinal thinning, lattice degeneration and peripheral breaks. (23,24)

Stickler syndrome

Stickler syndrome is an autosomal dominant collagen abnormality and can occur with or without ocular involvement. Whether the eye is involved depends on the gene affected. (25) Common ocular findings include: (19)

* Optically empty vitreous chamber or abnormal vitreous structure

* High myopia, which is typically present from birth but usually remains stable throughout adolescence

* Retinal detachment, which is typically bilateral

* Cataract

* Glaucoma.

Weill-Marchesani syndrome

Weill-Marchesani syndrome has a prevalence of one in 100,000, (26) and can present in autosomal recessive or autosomal dominant forms. (20) Ocular associations include:

* Small spherical lens only seen on full dilation (microspherophakia see Figure 4)

* High myopia

* Ectopia lentis

* Ultimately severe glaucoma or cataract. (20)

OTHER SYSTEMIC ASSOCIATIONS WITH MYOPIA

There are a number of systemic conditions in which myopia is a feature. The most prevalent of these are described below.

Homocystinuria

Homocystinuria is an autosomal recessive condition affecting the metabolism of the amino acid, methionine, which in turn leads to a build-up of the amino acid homocysteine in blood and urine. (27) Untreated it can cause multisystem damage, including brain, bone, cardiovascular and ocular problems, preventable by early diagnosis and treatment.

A principal feature of uncontrolled homocystinuria is subluxation of the crystalline lens; this is bilateral and approximately symmetrical, and can progress to a total dislocation of the lens into the vitreous. (28) Without treatment, 82% of patients will have developed ectopia lentis by 10 years of age. (29)

Patients with undiagnosed homocystinuria are likely to present at a young age, with rapidly progressive high myopia, as a result the lens subluxating. (30) All cases of unexplained lens dislocation should undergo prompt investigation as well as homocystinuria screening. A rapid progression of high myopia in patients who are already receiving treatment can be an early indication of poor control.

Myopia and a vibration of the crystalline lens on eye movement (phacodonesis) can occur prior to subluxation. In these cases, the refractive error tends to be spherical, which is a further indication that lens subluxation is not the mechanism inducing myopia at this early stage. (28) Myopia may result from degeneration of zonular fibres, resulting in a release of zonular tension, which allows spherical deformation of the lens (spherophakia). (31) Although there a lack of supporting evidence, it has been postulated that axial elongation of the eye in uncontrolled homocystinuria may contribute to myopia. (28)

[FIGURE 3 OMITTED]

Early commencement of treatment following prompt diagnosis can save or prolong life for the patient. It is important to identify other family members that may also have the condition due to its genetic nature.

Down syndrome

Down syndrome is a genetic abnormality of Chromosome 21. Well-known features of the syndrome include physical growth delays, widespread soft tissue abnormalities and variable degrees of intellectual impairment. Down syndrome has a known association with refractive, binocular vision and accommodative problems. Children and adults with Down syndrome generally have much larger than normal refractive errors. Hypermetropia is the most common finding in these individuals, however if myopia is present, it can be to a significantly high degree. (32)

Most developmentally normal children are born with significant refractive errors, most commonly, hyperopia. (33) These generally reduce towards emmetropia throughout childhood, as the eye develops and grows. (34) This process of emmetropisation does not appear to occur in Down syndrome despite there being a similar initial range of refractive errors. (35) Instead of these children outgrowing their ametropia and becoming more emmetropic over time, their refractive errors are often maintained or increase with age. (32,36) It has been observed that the rate of prescription change is related to the eventual refractive error rather than their refraction at birth. (36)

[FIGURE 4 OMITTED]

There is a high prevalence of strabismus in Down syndrome. While in normally developing children there is an association between hyperopia and strabismus, this is not true in Down syndrome. The sign and magnitude of ametropia seem irrelevant. The size or rate of change is not correlated with strabismus. (27)

It is obvious that the same assumptions and testing methods cannot always be used for children with Down syndrome. Careful, regular examinations should be carried out throughout childhood in order to monitor refractive error and binocular vision status.

Prematurity

It was previously believed that prematurity or low birth weight in the absence of ocular involvement was not a predisposing factor for higher than average incidence or levels of myopia. (37-40) However, long-term studies of refractive error have now shown that there is a higher frequency of myopia in these patients compared to babies carried to full term. (41,42)

High myopia has been associated with manifest retinopathy of prematurity for a long time. There are many ocular features and complications of retinopathy of prematurity including: avascularity of the peripheral retina, extra-retinal fibrovascular proliferation, vitreous haemorrhage, retinal detachment, leukocoria, and engorgement of retinal and iris vessels. In older children and adults, there can be reduced acuity and refractive findings of myopia as well as amblyopia and strabismus. It was initially thought that the effects of cryotherapy were responsible for high myopia in retinopathy of prematurity, however, it is now believed to be due to relative anterior microphthalmos (relative growth arrest of the anterior segment compared to the posterior segment). There is a known correlation between the severity of the condition and the frequency and degree of myopia.42,43

Cases of retinopathy of prematurity should be followed up yearly by an ophthalmologist due to the likelihood of late complications such as retinal detachment.

Cohen syndrome

Cohen syndrome is rare genetic disorder due to mutations in the VPS13B gene (frequently called the COH1 gene) with autosomal recessive inheritance. It is characterised by developmental delay, microcephaly, and hypotonia. Other features include progressive myopia, retinal dystrophy, joint hypermobility, and distinctive facial features: thick hair and eyebrows, long eyelashes, unusually-shaped eyes (down-slanting and waveshaped), a bulbous nasal tip, short philtrum, and prominent upper central teeth. (44)

CONCLUSION

High myopia in early life is a very significant finding and should be managed carefully as it could be the first sign of an important ocular or systemic condition. Children presenting with high myopia or significant myopia at an early age should be referred to an ophthalmologist for opinion and workup due to the high prevalence of ocular morbidity in these patients. Several of the conditions associated with high myopia are treatable or preventable if detected early so optometric intervention has the potential to improve visual outcome and in some cases even prolong or preserve life.

Course code: C-40358 Deadline: May 30, 2015

LEARNING OBJECTIVES

To be able to explain to patients about the implications of high myopia (Group 1.2.4)

To understand when it is appropriate to refer patients with high myopia into secondary care (Group 2.2.6)

To be able to identify systemic associations with high myopia (Group 6.1.13)

LEARNING OBJECTIVES

To be able to explain to patients about the implications of high myopia (Group 1.2.4)

To understand the potential systemic associations with high myopia (Group 8.1.4)

Exam questions

Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk/cet/exams. Please complete online by midnight on May 30, 2015. You will be unable to submit exams after this date. Answers will be published on www.optometry.co.uk/cet/exam-archive and CET points will be uploaded to the GOC every two weeks. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website (www.optical.org) to confirm your points.

References

Visit www.optometry.co.uk/clinical, click on the article title and then on 'references' to download

Fiona Cruickshank BSc (Hons), MCOptom, Nicola Logan PhD, MCOptom, FHEA, PGCertHE, and Manoj Parulekar MS, FRCS Ed, FRCOphth

Fiona

Cruickshank is an optometrist and PhD student at Aston University working in the field of myopia development with research funded by the College of Optometrists.

Dr Nicola Logan is a senior lecturer at Aston University and convener of the Myopia Consortium UK.

Manoj Parulekar is a consultant ophthalmic surgeon at the Birmingham Children's Hospital.
Table 1
Non-ocular indicators for various connective tissue disorders

Marfan syndrome               Stickler syndrome      Weill-
                                                     Marchesani
                                                     syndrome

* Long limbs and fingers      * Flattened facial     * Short fingers
* Tall and thin                 appearance             and toes
* Curved spine                * Cleft palate         * Short stature
* Sunken or prominent         * Large tongue         * Limited joint
  chest                       * Small jaw              movement/
* Flat feet                   * Arthritis              joint
* Crowded teeth               * Curved spine           stiffness
* Stretch marks on the skin   * Joint pain
  unrelated to weight change  * Hypermobile joints
                              * Mild to severe
                              hearing loss
                              * Learning
                                difficulties
                                due to hearing/
                                ocular impairment,
                                not  intelligence
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Title Annotation:CET: MYOPIA
Author:Cruickshank, Fiona; Logan, Nicola; Parulekar, Manoj
Publication:Optometry Today
Article Type:Clinical report
Geographic Code:4EUUK
Date:May 2, 2015
Words:2619
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