Contactologia 20 (1998) 165-169
Management of Myopic Anisometropic Amblyopia with Contact Lenses in Children
Presented in part at the IMCLS, Amsterdam 23.6-25.6.1998
R. G. MĂ©ly
Saarlouis, Germany
Abstract
One percent of the population suffer from anisomyopia of 3 DS and more. This error of refraction is a common cause of amblyopia.
Although children may compensate for relatively high degrees of aniseikonia, contact lenses should be preferred when anisometropia is greater than 6 Ds. Up to the 3rd or 4th year of life the use of extended wear silicone lenses is the safest method of correction. After the 4th year RGP-lenses worn on a daily wear basis are best.
Associated amblyopia can also be treated with contact lenses through the optical penalisation of the sound eye. The aesthetic and psychological advantages of this treatment improve compliance. Moreover, there may be a better chance of achieving binocular function under contact lens penalisation than under unilateral spectacle occlusion.
Key words: Amblyopia - Anisometropia - Contact lenses - Penalisation
Behandlungsmöglichkeiten der Amblyopie ex Anisomyopie mit Kontaktlinsen im Kindesalter
Zusammenfassung
Bei ca.1% der Bevölkerung liegt eine Anisomyopie von über 3 dpt vor. Dieser Brechungsfehler führt im Kindesalter häufig zu einer Amblyopie. Obwohl die Aniseikonie beim Kind wesentlich besser kompensiert werden kann als beim Erwachsenen, sind Kontaktlinsen ab 6 dpt Anisometropie das Korrektionsmittel der Wahl. Bis zum dritten oder vierten Lebensjahr sind Silikonlinsen im vT-Tragemodus zu empfehlen. Danach sollten formstabile hoch gasdurchlässige Linsen angepaßt werden.
Eine vorhandene Amblyopie läßt sich sehr gut mit einer kontaktoptischen Penalisation des besseren Auges therapieren. Die Entwicklung von binokularen Funktionen ist mit dieser Therapie besser als mit einer Okklusionstherapie. Die ästhetischen Vorteile dieser Behandlung verbessern zudem deutlich die Compliance.
Schlüsselwörter: Amblyopie - Anisomyopie - Kontaktlinsen - Penalisation
Traitement de l’amblyopie anisométropique à l’aide de lentilles de contact chez l’enfant
Résumé
Environ 1% de la population présente une anisomyopie égale ou supérieure à 3 dpt. Ce vice de réfraction est une cause courante d’amblyopie.
Bien que les enfants soient en mesure de compenser des degrés relativement élevés aniséiconie, les lentilles de contact constituent la correction de choix en cas d’anisométropie supérieure à 6 dpt. Jusqu’à l’âge de 3 ou 4 ans le port permanent de lentilles en silicone reste la méthode la plus sûre. Après l’âge de 4 ans un équipement en lentilles rigides perméables aux gaz en port journalier est préférable.
L’amblyopie associée peut égalent être traitée par pénalisation optique de l’oeil adelphe à l’aide de lentilles de contact. Il semble que grâce à cette technique les fonctions binoculaires puissent mieux se développer que sous traitement occlusif classique. Les avantages psychologiques et esthétiques de cette pénalisation optique par lentilles de contact améliorent d’autre part l’observance thérapeutique.
Mots clés : Amblyopie - Anisométropie - Lentilles de contact - Pénalisation
Introduction
Anisometropia
Anisometropia is a condition in which there is a difference in the refractive errors of the two eyes. According to Duke-Elder andAbrams (1970) the difference should be at least 2.5 DS. In Germany an anisometropia of 2 DS is considered a medical indication for the wearing of contact lenses.
Approximately 1% of the population suffer from an anisomyopia of 3 diopters and more. As shown on Fig. 1 based on a study by Höh, the incidence of anisomyopia decreases with severity according to a Gaussian curve. The gap between 0 and 3 diopters is due to the fact that only patients with anisomyopia of 2 diopters and more were included in the study.
On the basis of Joseph’s classification (Joseph, 1936) the following forms of anisometropia may be distinguished:
· composite anisomyopia (both eyes myopic, difference of at least 3 DS)
· simple anisomyopia (one eye myopic, the other emmetropic)
· hyperopic anisomyopia (one eye myopic the other hyperopic, the myopia must be higher than the hyperopia).
Unilateral high myopia
Zauberman and Merin (1968) define unilateral high myopia as a myopia of at least 5 DS, the refraction of the other eye being situated between +1.50 DS and -1.25 DS.
This unilateral high myopia is unusual. The incidence is estimated to be 10% of the high myopic population and only 0.3% of the normal population. In my own practice I found 33 cases of unilateral high myopia in 10260 patients. In their study about 563 amblyopic children, Simons et al. (1995) found only 4 cases of pure anisometropic amblyopia.
Unilateral high myopia is, in a very large majority of cases, related to an increased axial length of the eye (Höh 1991, Metge et al. 1994).
Some authors (Blatt 1924, Frenckel 1928, Sorsby 1951) believe that unilateral high myopia may be related to genetic factors.
Frequently associated pathologies are:
· corneal scars and injuries
· congenital cataract
· ptosis
· vitreous pathology.
These clinical observations confirm the experimental models of deprivation performed on monkeys.
Consequences on visual acuity and binocularity
Amblyopia can occur from unilateral image degradation up to approximately 7 years of age (Keech 1995). Even a low anisometropia of 1.5 to 2 DS is likely to cause amblyopia, especially if associated with astigmastism. There is a statistically significant correlation between the depth of amblyopia and the degree of the anisometropia (Kivlin and Flynn, 1981).
Anisometropic amblyopia appears to have a better treatment prognosis than strabismic amblyopia. According to Metge (1994) it is reversible in 50% of treated cases, although a full visual acuity of the amblyopic eye can seldom be attained. The prognosis of amblyopia is considered very poor when anisometropia is higher than 4 to 5 DS (von Noorden, 1981). Sanfilippo (1980) in his study of about 38 patients with unilateral high myopia ranging from -5 to -19 DS, treated by full-spectacle correction and occlusion found that 32% of the patients attained a visual acuity of 6/12 or better. The results of Sen (1984) are similar. Most authors consider the visual outcome very poor when unilateral high myopia is associated with unilateral peripapillary myelinated nerve fibers (Höh, 1991, Käsmann 1996). Nevertheless in a few cases unexpected good results are possible (Summer et al. 1991).
Optical aspects
Aniseikonia is smaller with contact lenses
As opposed to refractive anisometropia, the size of the retinal image in axial anisometropia is larger when corrected by contact lenses then with spectacles. In the study by Höh (1991) the difference in the retinal image size was only + 0.15% with spectacles, while when contact lenses were worn it was + 15.4% (Tab. 1). But his measurements of the aniseikonia by phase-difference haploscopy show clearly that the perceived difference is considerably smaller with contact lenses (-2.92%) than with spectacles (-19.25%).
This paradoxical observation is due to the fact that the retina of the myopic eye is elongated so that the receptors are spread further apart than in the fellow eye (Höh, 1991).
Side effects of spectacle correction
Spectacles have some negative side effects:
· Prismatic effects: The minus lenses of spectacles have the effect of a circular prism with its base facing outward. This leads to diplopia when the patients move their eyes from the 1° position.
· Aesthetic considerations: Aesthetic considerations are important in school children. Wearing thick glasses, especially with filters or patches, leads often to social and psychological problems (teasing at school). This may compromise compliance.
Therapeutic implications
A full correction of the refractive error and especially of any associated astigmatism is always necessary. A full spectacle correction is possible in cases of anisometropia up to 6 DS. Contact lenses provide a better correction in cases of more than 6 DS:
· Up to the age of 3 or 4 the extended wearing of silicon lenses is the more satisfactory method of correction.
· After the age of 4 RGP-lenses with high Dk may be worn on a daily wear basis.
Because of the higher risk of complications and their low Dk the extended wear of soft lenses is not recommended (MĂ©ly, 1994). New hydrogels with high Dk are currently been tested in clinical trials but are still not available.
Treatment of amblyopia
Amblyopia can be treated by occlusion therapy or by penalisation. Treatment must be started as soon as possible; after the age of 8, efforts are usually futile. The aim of the therapy is to improve the visual acuity of the amblyopic eye and to restore binocularity.
Occlusion therapy
The sound eye is usually covered by a patch. In some cases occlusion may also be performed with occluding contact lenses. Various patching regimens are possible:
· Full-time occlusion may be used initially in severe cases and in assessment.
· Partial occlusion can be used at the beginning or at the maintenance stage.
There is little question regarding occlusion’s efficacy in improving visual acuity in the amblyopic eye but the question of the degree to which unilateral occlusion may compromise binocularity remains unresolved (Simons et al. 1997).
Penalisation
Penalisation consists in blurring of the sound eye for near or distance vision or both by pharmacological or optical means. Penalisation is most effective in moderate cases of amblyopia (20/100 or better uncorrected) and in the prevention of the recurrence of amblyopia (von Noorden 1986). It should be considered more often in the primary treatment of amblyopia (Repka, 1993). The advantages of penalisation versus occlusion are:
· It avoids the social stigma of the patch and therefore improves compliance
· It cannot be removed by the child like a patch or glasses
· There is no skin irritation
· It is safer because it preserves a full visual field
· It allows stimulation of binocular functions because it reduces only the high but not the low-spatial frequency input to the treated eye.
· Atropine penalisation
Atropine penalisation consists in blurring the sound eye for near vision by pharmacological means. It can also be combined with glasses for optical penalisation . This method may be as effective as occlusion ( Simons et al. 1997) but has some disadvantages:
· There is a potential for development of reverse amblyopia
· A phototoxic insult to the retina (UV-Radiation) seems possible
· The children are bothered by brightness outdoors.
· Optical penalisation with contact lenses
Contact lenses are the best method for correcting the refractive error in cases of unilateral high myopia. Although they also provide a very effective and flexible way of treating the amblyopia by optical penalisation of the sound eye there are few reports in the literature of this method of treatment (Elmer et al. 1981). As opposed to pharmacological penalisation, the timing and the degree of blurring can be adapted to the therapeutic results. RGP or disposable lenses may be used on a daily wear basis for this purpose.
Of course, contact lenses have also some disadvantages:
· The fitting of contact lenses (especially RGP-Lenses) in young children may be a difficult business
· Some parents may experience handling problems
· The risks inherent to contact lens wear cannot be denied
· They are more expensive than occlusion therapy or atropine penalisation.
Case Report
Sandra was 6 years-old when she came for the first time to my practice. She was sent by her GP because of a very bad visual acuity on one eye and a lack of stereopsis.
The uncorrected visual acuity was:
OD = 0.05
OS = 0.4
The cycloplegic DS error was:
OD: - 8.0 sph (-1.75 cyl 180°)
OG: -1.0 sph (-1.0 cyl 175°)
There was no stereoscopic vision. The fixation was centric. The orthoptic examination revealed a microstrabismus OD. The anterior segment and the fundus were normal.
The initial treatment consisted in a spectacle correction and a full-time occlusion therapy by patching the left eye 6 days/week
After 8 weeks of full spectacle correction and occlusion therapy the visual acuity with spectacles was:
OD = 0.4
OS = 0.8
There was an esotropia of the right eye with a deviation angle of 3°, the Bagolini striated glass test was positive, there was still no stereopsis
5 months after the beginning of this treatment I decided to fit RGP-lenses for the following reasons:
· there was no further improvement of visual acuity or stereopsis
· Sandra had developed a mild skin irritation due to the patch
· Contact lenses seemed on a long term basis the best way to correct her high anisometropia.
The keratometric readings were:
OD: 7.11/0° and 6.63/90°
OS: 7.05/0° and 6.74/90°
3 RGP-Lenses with high Dk were fitted (Menicon Super EXĂ’)
OD: 7.0/-8.25/10
OS: 7.0/-2.0/10
OS: 7,0/+4.0/10
These lenses were worn on a daily wear basis. The plus 4 diopters penalisation lens was worn every second day. After two months of contact lens wear and optical penalisation the visual acuity with contact lenses was:
OD = 0.8
OS = 0.8 (with the -2,0 DS lens)
OS = 0.1 (with the +4,0 DS lens)
The Bagolini striated glass test was positive and Sandra had developed a stereoscopic acuity of 140 seconds of arc (Titmus Test).
The penalisation had to be stopped after one year because an esotropia of the left eye occurred when the plus 4 diopters lens was worn. No loss of visual acuity could be observed after ceasing of the penalisation.
Only minor problems occurred in 3 years of follow up:
· 3 lenses were lost
· One episode of red eye with punctate keratitis in January 1998 was easily resolved after refitting.
After 3 years of follow up, the visual acuity with contact lenses is excellent:
OD = 1.0p
OS = 1,0
There is still a microesotropia of the right eye with an angle of deviation of 1 to 4 prism diopters (far, alternate prism cover test). The stereoscopic acuity is 240 seconds of arc (TNO-Test).
No increase of the myopia has been observed.
Conclusion
In conclusion, this case demonstrates that:
· Contact lenses are the best way to correct the refractive error in case of unilateral high myopia
· The contact lens penalisation is an effective and very aesthetic method of treating the amblyopia:
· an outstanding improvement of the visual acuity is possible
· penalisation may improve binocularity better than occlusion
· The prognosis may be good even if anisometropia is greater than 6 diopters and after the age of 6.
· In accordance with larger studies of other authors (Grosvenor 1991, Elie 1998) RGP lenses may reduce the rate of progression of myopia.
· Contact lenses may be very useful to improve compliance when occlusion therapy fails because of psychic and social problems of the children or their parents (Summers and Egbert, 1996). In such cases they improve not only vision but also quality of life.
Paediatric ophthalmology should benefit from the recent developments in the field of contact lenses:
· New materials for RGP-lenses with very high Dk have been introduced in the past years and new materials with a very high oxygen transmissibility for soft lenses will also be available in the near future.
· New concepts (one day disposable lenses for occluding or penalisation) have revolutionised the wearing of contact lenses.
These new developments will allow a safer, cheaper and more flexible use of contact lenses. For all these reasons contact lenses should be considered more often in the treatment of refractive errors and amblyopia in children.
References
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Received 28.6.98, accepted 16.7.98
Dr. René G. Mély
Kaiser-Friedrich-Ring 30
D-66740 Saarlouis
Fig. 1: Frequency distribution of anisomyopia (based on Höh, 1991)
Tab. 1: Differences in retinal image sizes and aniseikonia (perceived difference in image size) determined by phase difference haploskopy , based on Höh 1991
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