Amblyopia
Amblyopia is the term used to describe reduced vision in one or both eyes due to them not being stimulated properly in childhood.
The term is often interchangeably used with ‘Lazy Eye’. Lazy eye is a non-medical term, usually used to describe a squint (strabismus, or a turn in the eye), poor vision, or a droopy eye-lid (a ptosis).
Amblyopia is the leading cause of vision loss in children and occurs even when there is no problem with the structure of the eye.
The decrease in vision occurs when one or both eyes send a blurry image to the brain. The brain then “learns” to only see blurry with that eye, even when glasses are used.
Only children can get amblyopia and if it is not treated, it can cause permanent loss of vision.
Amblyopia is most often caused by a need for glasses or a squint (strabismus), or a combination of both. It can also happen if there is anything interfering with the visual pathway, for example a cataract, or a droopy eyelid (ptosis).
The end result of all forms of amblyopia is reduced vision in the affected eye(s). However, measuring vision in young children can be difficult.
Parents may not think there is a problem because their child’s eyes may look straight. Also, the “good” eye may have normal vision, so the child may appear to see as well as other children. For these reasons, amblyopia in some children may not be found until the child has a vision screening test.
Maybe, but they may not correct it all the way to 100%. With amblyopia, the brain is “used to” seeing a blurry image and it cannot interpret the clear image that the glasses produce. With time, however, the brain may “relearn” how to see and the vision may increase.
The first step is prescribing the glasses and getting the child to wear them full-time. The earlier the child starts to wear the glasses, the quicker they will get used to them.
Following a period of time in full-time glasses, the child is reviewed in the eye clinic, usually about 3 months later. If there is amblyopia at this visit, the child may need to start patching.
Early treatment is always best.
If there is a squint, treatment will probably need to be completed by the age of 7. Other types of amblyopia may respond to treatment beyond this age, however, the earlier treatment commences, the better chance of success.
See the section on Amblyopia Treatment
AMBLYOPIA TREATMENT
One of the most important treatments of amblyopia is correcting the initial cause of the amblyopia, ie, the refractive error, the cataract, etc. This may improve vision.
ollowing this, treatment is started to encourage use of the non-dominant eye. This is usually done by patching the good eye, or using Atropine eyedrops to blur the good eye.
Treatment should be carried out under supervision, and with regular appointments to monitor progress.
Many parents find that coloured patches can improve compliance.
Although an improvement in vision frequently occurs within weeks of beginning patching treatment, optimal results often take many months. Once vision has been improved, part-time (maintenance) patching or periodic use of Atropine eyedrops may be required to keep the vision from slipping or deteriorating. This maintenance treatment may be advisable for several months or years.
Your orthoptist will recommend how much patching should be done. This will be based on the level of vision, the cause of the amblyopia and the age of the child. It is usually best to use an adhesive patch that sticks onto the face, to ensure that there is no peeking. If glasses are worn, they should be worn over the patch.
Most types of adhesive patches are hypoallergenic. However, a skin reaction is still possible. If this occurs, try a different brand, or your orthoptist may recommend a non-adhesive ‘extension’ patch. Alternatively, Atropine therapy may be advised.
Patching is never easy for the child (or the parent!), particularly when the sight in the amblyopic eye is very poor. However, there are ways to make it easier, for both the child and the parent. Coloured patches are now available and are often preferred. Simple star charts can be a valuable means of encouragement. Use a patch that peels off painlessly, or merely ‘tickles’. Many people find it best to patch at the beginning of the day as part of the daily routine. In older children, they may be too self-conscious to wear the patch at school, but it can work well in younger children.
Reward charts can be a really effective way of encouraging children to wear their patch every day.
When patching, any activity that uses the eye is effective, possibly the more detailed the better, for example, drawing, reading, using a computer, or even watching TV. This can work particularly well as it distracts the child and stops them from thinking about the patch.
Remember that the younger the child the more effective the treatment, but one of the most common reasons for the treatment not working is poor compliance.
Surgery on the eye muscles is a treatment for strabismus (squint) – it can straighten misaligned eyes. By itself, however, surgery does not usually help the amblyopia.
Amblyopia treatment is usually done before strabismus surgery is considered.
Children who have strabismus surgery under the age of 7 can still develop strabismic amblyopia afterwards, and still need close monitoring and treatment for this.
In some cases, treatment for amblyopia may not succeed in substantially improving vision. It is hard to decide to stop treatment, but sometimes it is best for both the child and the family. Children who have amblyopia in one eye and good vision in their other eye, can wear safety glasses and sports goggles to protect the normal eye from injury. As long as the good eye stays healthy, these children function normally in most aspects of society.
There has and continues to be extensive research into the causes of and optimal treatments for amblyopia. The following are just a few examples of where to go for further reading:
The PEDIG group in the US have published papers on amblyopia treatment, see www.jaeb.org for details.
Interventions for unilateral refractive amblyopia. Cochrane Database Syst Review 2008
Conventional occlusion versus pharmacologic penalization for amblyopia. Cochrane Database Syst Rev. 2009
Interventions for strabismic amblyopia. Cochrane Database Syst Rev. 2011
Patching, or occlusion, is done in childhood to treat amblyopia, or a lazy eye. It works by stimulating the poor eye and thus developing better sight.
Atropine is a dilating eye drop used topically to temporarily paralyze the accommodation, or focussing, reflex of the eye.
It is sometimes used in the treatment of amblyopia. By dilating the pupil of the good eye, the sight is blurred, particularly for near work, forcing the amblyopic eye to work.
Binocular Vision
Binocular vision, or binocularity, means the ability to use the two eyes as a pair. They are co-ordinated and obey certain physical laws of innervation. Binocular vision is the basis for stereopsis, or 3D vision, and straight eyes are essential for its development.
Glasses
Glasses are prescribed to children after they are tested for refractive errors, which is the need for glasses. In children, eye-drops, usually cyclopentolate, are used prior to a refraction to dilate the pupils and the test is carried out. There are different types of refractive errors. See below:
Hyperopia (Hypermetropia, Farsightedness, Or Longsightedness)Hyperopia is a refractive error of the eye, causing a difficulty in near focussing, although in high amounts, it affects all distances. It is usually caused by the eyeball being too short in length, or by the cornea in the front of the eye being too flat. This results in an inability to focus light rays sharply on the retina, which causes blurred vision.
This condition is present at birth, and tends to improve with time as the eye grows. In fact, it is normal to be born with a low amount of hyperopia. Moderate to large amounts of hyperopia in children can cause accommodative esotropia and amblyopia.
Hyperopia is sometimes confused with presbyopia, see below.
Myopia (Shortsightedness, Nearsightedness)Myopia is an optical anomaly within the eye, causing distance vision to be blurred, and near vision to be clear. There can be different causes, but it is usually caused by the eyeball being too long, or the cornea at the front of the eye being too curved.
Myopia can be present at birth, but this is uncommon. It is more usual to develop later in childhood, or during the early teens, and tends to worsen as the eye grows.
AstigmatismAstigmatism is a common optical defect of the eye, where there is a difference in the degrees of refraction in different meridians of the eye. This causes vision to be blurred or distorted at all distances, as the eye is incapable of focussing an image sharply. It is usually caused by the cornea, or the front part of the eye, being an irregular shape. A common analogy used is the description of the eye being shaped like a rugby ball instead of a (spherical) football.
Astigmatism can be corrected with glasses, using a lens that has different radii of curvature in different planes, known as a cylindrical lens. It can also be corrected with contact lenses or refractive surgery.
PresbyopiaPresbyopia is the term used to describe the inability of the eyes to focus on near objects as a person ages, giving rise to the need for reading glasses. The usual age of onset is between 40 and 50 years.
Glasses And ChildrenWe are often asked how it can be possible to know if a child, or even a baby, needs glasses.
For this, a refraction, or retinscopy , is carried out, usually by an ophthalmologist, after dilating the pupils. Dilating the pupils is necessary because the examiner must observe the movement of a light on the red reflex on the retina, using a retinoscope.
This process objectively measures the refractive error of the eye. It can usually be done quickly, accurately and with miminal co-operation from the child.
If there is a significant refractive error, glasses are recommended, or the child may be closely monitored at regular appointments until it becomes apparent that they would benefit from glasses. At these appointments, the orthoptist will assess vision and make sure the eyes are working together. If there is any sign of amblyopia, or a squint, a prescription for glasses may be recommended.
Usually it is recommended that the glasses are worn full-time. As the eyes are growing throughout childhood, it is often difficult to say initially for how long the glasses will need to worn.
Parents are often concerned that the child won’t want to wear the glasses, that they may be teased at school, or that the child may be restricted in playing sport. We find that this is now rarely a problem, because of several factors. There is a great choice of children’s glasses available, and it can be a good idea for the child to be encouraged to choose their own pair, e.g., a favourite colour or cartoon character. Harry Potter has been a great advocate for children’s glasses! As well as this, as services have improved, we have become much better at picking up problems earlier, and therefore, it is not unusual to see young children wearing glasses. This has made it much more socially acceptable.
Wearing glasses for sport can be a problem in older children, when sport becomes more physical. However, there are now sports glasses available, which can be worn for football, rugby, GAA.
Strabismus (squint)
Strabismus is the correct term for any misalignment of the eyes. It is often called a squint, a crossed eye, or a turn in the eye. There are many different types. Strabismus is usually categorised according to the direction of the turn. An inward (converging) turn is called an esotropia. An outward (diverging) turning eye is called an exotropia. Vertical strabismus occurs when the eye turns downwards, called a hypotropia, or upwards, called a hypertropia. It is also possible but much less common for the eye to be twisted out or in. This is known as a cyclotropia. Strabismus can occur in childhood or adulthood, depending on the cause.
Esotropia
An esotropia refers to an inward turn of the eye. It is sometimes described as a ‘crossed eye’. There are many different types. In childhood, it is often caused by uncorrected hyperopia (long-sightedness).This is known as an accommodative esotropia.
Accommodative esotropia (convergent squint), refers to an inward turn of one eye, and is caused by the focusing efforts of the eyes as they try to see clearly. Patients with accommodative esotropia are typically longsighted (hypermetropic, or hyperopic). This means that the eyes must work harder to see clearly, particularly when the object is up close. A side effect of this focusing effort can be excessive convergence, or crossing of the eyes.Child with accommodative left esotropia
If a child’s eyes cross at an early age, then vision may not develop normally. Vision can be reduced in one eye (amblyopia) if it is not “used” properly during childhood, and fine depth perception may never develop.
Crossing of the eyes is never normal. However, some babies or small children may look like they have a turn in the eye, but on examination, actually be normal. This is called a pseudosquint.
Initial treatment for accommodative esotropia usually involves the prescription of glasses for the long-sightedness. By letting the eyeglasses do the work, the eyes can relax their focusing. This will reduce the convergence or crossing, and the eyes will straighten as they relax.
Glasses which are used to treat accommodative esotropia should be worn full time.
Once the child has settled in to their glasses their eyes may become fully straight with their glasses on, or partially straight with their glasses on. The child will typically have their vision tested with their orthoptist every two to three months to monitor their progress. If the vision is reduced in one eye, this is called amblyopia, and patching treatment may be required.
Surgery is only indicated if the eyes are still significantly crossed even with the glasses on. Your orthoptist or ophthalmologist will advise if and when this is an appropriate course of action. Surgery for accommodative esotropia does not eliminate the need for glasses but rather fixes the amount of crossing that is “left-over” when the glasses are on. The eyes will likely continue to cross somewhat when the glasses are off.
Even after a child has been successfully wearing glasses to treat accommodative esotropia, it is still normal for the eyes to continue crossing without the glasses. In fact, sometimes the crossing may be even more noticeable than it was before the child started wearing glasses as they focus harder than ever to achieve the clarity of vision they get with their glasses. The important matter is their vision, and whether or not the eyes are sufficiently straight and controlled with the glasses on.
In some cases, children will have particularly excessive amounts of eye crossing (esotropia) when looking at objects up close, such as while reading. These children may benefit from making the lower, reading area of the eyeglasses “extra strong” in the form of a bifocal lens, as shown here:
Yes, children can outgrow accommodative esotropia. This usually happens during the late primary school and adolescent years as a child becomes less longsighted. It is difficult to predict early in childhood whether or not any given child will outgrow their need for glasses. As a general rule children requiring a prescription of +4.00 or more will rarely completely outgrow their glasses.
Yes in most cases when they are old enough (current recommended age 21) they can seek refractive surgery. Once treated, you can expect the esotropia to be very similar to that with their glasses on.
Contact lens treatment is at the discretion of the optometrist. A typical age to start contact lenses might be between 14 and 16 years, with awareness of good hygiene being of the utmost importance.
Exotropia
Exotropia, or divergent squint, refers to an eye that turns or diverges outwards. Exotropia may occur from time to time (intermittent exotropia) or may be constant. You may only notice one particular eye drifting out, or it may be either eye that deviates, known as an alternating exotropia.
These types of exotropia usually begin in early childhood. Congenital exotropia is more unusual, and often indicates poor vision or an ocular pathology.
Some people have a tendency for their eyes to drift outward when their eyes are completely relaxed, such as when they are “staring off into space”, or when looking in the far distance. This outward drift, which occurs only in those moments of visual inattention, can be controlled when visual attention is refocused. The exotropia may occur rarely and result in few or no symptoms. However, in some people it may become more frequent or even progress to the point of becoming constant.
Intermittent exotropia in the right eye
People with intermittent exotropia may experience an outward drift only occasionally, such as when they are very tired, feeling sick, or after drinking alcohol, despite their efforts to refocus. Some patients may experience double vision (diplopia); others say that they can feel that an eye is misaligned, even though they do not see anything unusual. Others are unaware that an eye is turning, unless another person mentions it to them.
Children with intermittent exotropia commonly close or squint one eye at times, especially when they are exposed to bright sunlight. The exact reason for this is not clear. Small children who won’t wear sunglasses may be offered a hat with a brim, such as a baseball cap, to shield the eyes from the sun, thereby limiting the need to close one eye.
In many cases where the exotropia only occurs infrequently, then often there is no effect on the child’s eyesight. If the exotropia becomes more constant, then the deviating can become under-used and amblyopia (reduced vision) may develop. It is important therefore to have regular vision checks with your orthoptist. If amblyopia develops your orthoptist may recommend patching or an atropine regime. Of course, if your child is shortsighted or longsighted this should be corrected with glasses.
Keeping the child as well rested and healthy as possible will help. Feeling sick or having a fever may cause the intermittent exotropia to temporarily occur more frequently.
Your orthoptist or ophthalmologist may recommend eye exercises or minus (concave) lenses if they feel your child will benefit.
Exercises involve improving the child’s ability to convergence their eyes and/or training them to become more aware of when their eyes are deviating so that they can learn to control it better.
Minus lenses (glasses with a prescription such as -1 or -2 etc.) stimulate the eyes to focus harder. As the eyes focus (accommodate) they also converge (turn in) which helps to control the divergent angle. Eventually the child would be weaned off the glasses in the hope that they can maintain control of the exotropia themselves.
In cases where the exotropia persists after exercises and minus lenses, then strabismus (squint) surgery may be required. Children who undergo surgery at an older age may have better outcomes and treatment. Exercises or minus lenses can help to keep their eyes working together until they are an optimum age for surgery. Your orthoptist and ophthalmologist will discuss the ideal timing of surgery for your situation.
Binocular vision refers to the brain’s ability to see objects with both eyes simultaneously. It is only possible when the eyes are straight and not when the exotropia is present. Among other benefits, binocular vision is necessary for normal depth perception, or “3-D vision”. Children who are capable of maintaining binocular vision are also less likely to develop amblyopia.
Exotropia in an eye with very poor vision is called sensory exotropia. In this case, the eye with low vision is unable to work together with the other eye, and therefore, the poorly-seeing eye may have a tendency to drift outward.
Sensory exotropia may occur at any age. Of course, if the visual problem is treatable, it should be addressed as soon as possible. Surgery to cosmetically straighten the eye may be possible.
Age is not the main determining factor for exotropia surgery. The surgery is appropriate when exotropia is worsening and is present for the majority of the time. However older children may have better long term outcome
Pseudo-strabismus
Strabismus is the medical term for eye misalignment, or squint. Pseudo-strabismus refers to a false appearance of strabismus. Most often, one or both eyes have the false appearance of turning inward (See figure below).
The skin fold at the inner corner of the eyelids can be broad and is often associated with a broad flat nasal bridge (epicanthal folds, or epicanthus). These features contribute to a cross eyed appearance since there is less space (white area) between the iris and the inner corner of the eyelid. This is especially noticeable in pictures, or if the child is looking at you from an angle.
The child pictured appears to have an esotropia, or convergent squint. In fact, on examination, the eyes are straight.
This basic test can be performed on any child using a penlight. As a child focuses on a penlight, the position of the light reflection from the front surface (cornea) of the eye is observed. The test is accurate only if the child looks directly at the light and not to the side. Normally the corneal light reflex is centered on both pupils. The test is abnormal if the corneal light reflex is “off-center”, or asymmetrical (see below).
True strabismus in a child can lead to permanent vision loss and is best treated early. If a child is suspected of having strabismus, a complete eye examination is recommended.
It is often difficult to differentiate between true strabismus and pseudo-strabismus.
Pseudo-strabismus is common, especially in young babies, and does not require treatment. As facial features mature, the widened nasal bridge tends to narrow, and the appearance tends to improve with time.
Asian children may retain a broad nasal bridge into adulthood and this is perfectly normal.
School Screening
Vision screening is an efficient and cost-effective method to identify children with visual impairment, or eye conditions that are likely to lead to visual impairment, so that a referral can be made to an appropriate eye care professional for further evaluation and treatment. Up to 6% of pre-school children will have an ocular or vision defect requiring treatment or follow-up.
Vision screening in Ireland is carried out under the guidance of ‘Best Health for Children’, the screening and surveillance programme of the HSE. Updated guidelines for school-entry screening are due to be published in December 2016.
There are a number of methods used to screen a child’s vision. The method chosen is largely dependent on the age and co-operation of the child being screened and the experience of the examiner.
Best Health for Children recommends the following:
Preschool Children:
- Observation of visual behaviour.
- Use of clear referral criteria: history of amblyopia or squint in first degree relative AND parental concern.
Primary School Children:
- School entry screening is carried out in all Junior Infants.
- Clear referral criteria: visual acuity of less than 0.2 LogMAR in one or both eyes (December 2016).
When testing vision, a linear crowded logMAR test at 3 metres, with an adhesive patch is the ideal, using a letter based test, e.g. Keeler or Sonksen.When testing, it’s important to use a test with ‘crowding’, for example, a line of letters or pictures, as opposed to a single letter or picture.
Amblyopia causes blurring of letters in the centre of the line, but not the outside. Hence, the child may be able to identify a single letter at 6/6, but in reality, may only see 6/18 on linear testing.
It is now recognised that using a LogMAR test is a more accurate method of measuring visual acuity. For more information on Snellen and LogMAR vision, see here.
Best Health for all Children Revisited recommends that ideally, screening should be carried out by orthoptists. However, in most areas, designated school nurses screen during the school year.
For further reading on orthoptist-led screening with particular reference to the U.K., see here.
The main goal of vision screening is to identify children who have or are at risk to develop amblyopia, which can lead to permanent visual impairment unless treated in early childhood. Other problems that can be detected by vision screening include strabismus, cataracts, glaucoma, refractive errors such as myopia, hyperopia and astigmatism, ptosis and other more serious but rare conditions.
Vision screening is most effective when performed at as young an age as possible. The earlier a problem is detected, the better the chance to obtain maximal vision through appropriate treatment.
If a child fails school entry vision screening, the child should be referred for a comprehensive eye examination at your local eye clinic.
Children who fail the school exit screening are encouraged to attend their local optician.
Best Health for Children is available to view online through the HSE website here.
A comprehensive training programme for public health nurses, area medical officers and school nurses was published in 2005, and is available to view and download as a PDF on the HSE website here.
