This information will help you to put complex visual jargon and measurements into more manageable terms.
A regular eye examination is very important, however getting bogged down with technical terms can make understanding your child’s visual abilities some what difficult. Below are examples of some terminology you may have come across.
If your child is attending the eye department at the hospital they will encounter different health care professionals at different times. All departments work together so that your child receives the best care possible.
Vision & Learning
Having a regular eye test and an updated pair of well fitting glasses allows the child to use what vision they have to the best of their ability (See ‘Well fitting frame’).
Vision plays an important part in our lives. This is especially true when it comes to learning. If a child has a visual impairment this can hinder the learning process, as teaching and learning is mainly based on visual tasks. Small steps can help make visual dependant learning easier. Optometrists, healthcare professionals, parents, and teachers must make learning as enjoyable and as easy as possible.
Any excess effort to see will cause the child to tire more easily and will reduce the thinking power for understanding visual information. Some children’s eyes can’t work together due to different reasons such as amblyopia (lazy eye) or a strabismus (squint) so therefore their depth perception (3D vision) is reduced.
Another common feature is nystagmus (eyes wobble), this can make fixation difficult, and reduces reading speed. This extra effort can put increased pressure on the visual system, and subsequently on the child can tire more easily. This is noticeable towards the end of the day; a nap during school if possible helps. Quite often this isn’t practical and older children will need a break or a lie down in the evening before starting homework.
You may notice a head tilt or turn when a child is looking at something of interest or trying to concentrate on something visually. This head position called ‘the null point’ which is unique to them, is adapted subconsciously and shouldn’t be corrected. It allows the nystagmus movement to lessen and become more controlled in that particular position, thus improving their focus and vision. Small adjustments can make reading and fixation a little easier such as
- Placing finger on page of good / high contrast reading material,
- Clean school black/white board free from glare and dust,
- Closing blinds on sunny days,
- Slanted boards for reading.
- Preference seating (toward front of the classroom)
- Providing a classroom assistant to help out, flag up problems, or photocopy material into larger print (ask your optometrist / GP/ Ophthalmologist or Social Services about ‘Statementing’).
Importance of a regular eye examination
Lots of useful information can be gathered during an eye test. The optometrist will make the eye examination as fun and as interesting as possible. Different letter and picture charts are used, and quite often little lights are shone into the eyes for an eye health and prescription check.
As discussed previously (see accommodation) from time to time drops are required to get a gold standard base line measurement of your child visual function. The eye drops (cycloplegic drops) can sting for a few seconds, and temporarily remove the eye muscles ability to accommodate (focus) thus as parents you will notice the large pupil, and the child may report some blurred vision. But these are only temporary and the benefits from an eye test of this kind are vast. This type of refractive eye test is necessary as children’s eyes change a lot as they are developing; but as the child grows they will need the drops instilled less and less.
It is very helpful to bring some dark sunglasses for the way home as this will make things much more comfortable until the effects wear off (12-24 hours later).
Accommodation is the process by which the optical power to maintain a clear image on an object as it draws near the eye. In other words the eye changes the shape of the lens in order to bend the light rays from a near object to focus on the retina (see figure 5 below). The more long sighted a person is, the more the eye has to work. This continued strain can result in headaches and tired eyes. The eyes ability to accommodate gradually reduces over time. An adult in their early to mid forties will begin to notice that near print is no longer clear, and that they now need reading glasses (a positive lens will bend the light onto the retina- this person is experiencing Presbyopia (age related loss of accommodation) which is perfectly normal). The young human eye can change focus from distance to near (7 cm from the eye) in 350 milliseconds!.2 This can make measuring a child’s refractive error (strength of glasses) very difficult. The young eyes ability to change focus so quickly combined with a child’s behavior (i.e. looking around room from distance to near) means that the eyes power fluctuates dramatically. In order to ascertain an accurate baseline measurement of a young child’s refractive error the optometrist will use cycloplegic eye drops (note: these may sting for a few seconds). Parents will notice a large pupil as the eye drops temporally prevent the eye muscles ability to accommodate (change focus); this is a gold standard optometric procedure and its importance is paramount. As a child gets older they will need the drops less and less, as co-operation increases.
Is the term used for a ‘lazy eye’. It is an eye that has more reduced or poorer vision than the other. Usually an amblyopic eye is a healthy eye that cannot be corrected with glasses (to achieve a ‘normal level’ of vision) due to poor development. Quite often a child with amblyopia or a lazy eye has or can develop a ‘strabismus’ or squint. The brain will begin to ignore the blurred image coming from the affected eye. Optometrists and orthoptists work together to try to prevent amblyopia occurring; using glasses (giving the poor eye as clear an image as possible) and also sometimes with patching (patch good eye to force poor eye to see). This can be done whilst the eye is developing, but once the child is approximately 8 year old, the visual system is fully formed and cannot be manipulated. Amblyopia therefore cannot be reversed after this age.
Astigmatism usually means that the front surface of the eye is shaped of like a rugby ball. It is very common in both visually normal and visually impaired individuals. Two main curves are found: one flatter and the other steeper. This shape causes light to focus in two different positions where the more curved area focuses further forward and the less curved focuses further back. The effect on vision is to distort objects, so similar shaped characters become confused. For example, the letter 'G' may be confused with a 'C' and the number '2' may be mistaken for the letter 'Z'. This can be easily corrected with a combination of lenses (so that your prescription is written a little longer as discussed below).
The direct comparison of one objects colour or intensity to another i.e. a letter chart has black letters on a white background, this gives high contrast; however, for example newspaper can demonstrate poor contrast, with grey writing on a grey back ground i.e. The weather in the UK is fluctuating., resulting in the loss of fine detail. If someone has poor contrast sensitivity it means they can see high contrast objects (i.e. Black buttons on a white coat) however they can’t pick out blue buttons on a blue or busy patterned coat. Quite often individuals with poor contrast sensitivity also have a visual impairment. Poor contrast sensitivity can explain problems at school were reduced quality photocopied examples of work sheets prove difficult to read (even if they are in large print). An illustration of good or high contrast can be seen at some low vision centres were red plug sockets are placed on white walls, this allows some independence instead of a person with low vision trying to locate a white plug socket on a white wall. The same applies to children and games in particular. Using un-crowded / uncluttered pictures will make stories much easier to see and follow. A bright high contrast ball incorporated for games prevents exclusion of a visually impaired child. Parents can sometimes wear bright distinctive clothing, making it easier for their child to pick them out from a crowd. Another helpful feature often over looked is lighting. It is useful to make use of task specific lighting i.e. placing a lamp on a desk to do homework, rather than simply relying on lighting from the main ceiling light bulb in the room. Often optometrists will recommend a good ‘day-light bulb’ and ‘angle poised’ light to increase the visibility and contrast of reading material.
This test aids in diagnosis of some conditions, it measures the amount of electrical activity along the visual pathway. Skin sensors / electrodes are placed on the scalp or eyelid, and a flashing light or checkerboard pattern is shown to the individual. Brain or electrical activity is then recorded via the little sensors. This procedure is painless.
Hypermetropia - Long Sightedness
Hypermetropia is a common sight problem that affects someone’s ability to see close-up objects. Commonly known as long-sightedness, the condition is a type of focusing error of the eye that can be corrected with positive (+) plus lenses. Long-sighted, or Hypermetropia, means the eye focuses the rays of light "behind" the retina, rather than on it (see figure 3 below). This makes it difficult for the long sighted person to see objects close up. However, because the eye is able to naturally accommodate (were the lens can change shape and’ fatten’ to cause light to bend more), this enables the light rays to be focused on the retina. Distance vision is usually good; however when the same individual tries to look at something up close, much more effort is required, as light from a near object will fall much further back behind the retina. Near vision is therefore worse, and this prolonged effort over a certain period of time will result in eye strain, tiredness and headaches.
Myopia - Short Sightness
Short-sighted, also known as near-sight or Myopia. This makes it difficult to see distance objects, whereas objects close-up are clearer. Myopia or short-sightedness occurs when the eye focuses the rays of light in front of the retina, rather than on it (see figure 4 below). This is believed to happen when the eyeball is slightly too long. Thus distant objects are blurred without glasses (negative corrective lenses are used).
(Dancing or wobbly eyes) Nystagmus is an involuntary flickering movement of the eyes, which makes fixation difficult and can reduce reading speed. It is a mechanism the eye muscles and visual system adapt in order in to search and fixate in space. Often nystagmus is noticed during the first few months of life. Nystagmus comes in different forms and the eyes can move in various directions and speed. Quite often nystagmus can be more noticeable at different times of day, with stress, tiredness or in different positions of gaze. Vision is always affected to various degrees. The constant movement of the eyes minimises the ability to focus and this reduces the capability to obtain optimum vision.
An Ophthalmologist is a medical eye specialist or eye doctor who deals with diagnosis and the health of the eye, and child. They also can perform surgery and prescribe drug medication as necessary. The ophthalmologist has the ability to request registration for an individual as blind (severely sight impaired) or partially sighted (sight impaired).
An Optometrist or Optician checks the child’s vision, prescribing glasses and low vision aids as necessary. An optometrist can also assess the health of the eye, make an initial diagnosis, manage some cases or refer a patient if necessary.
An Orthoptist will look at the eye movements paying close attention to the eye muscles, and is mainly interested in binocular vision. In particular Orthoptists are involved in the management of squints (were an eye turns in or out) or a lazy eye where the vision is poorer in that eye and patching (of the good eye) is some times indicated. They also assess any unusual head tilts associated with nystagmus (which is an involuntary repetitive to-and-fro movement of the eyes, and is noticed in the first few months of life).
The power or strength of corrective lenses / glasses. A glasses prescription can be in the form of positive (+) or negative (-) lenses, depending on whether a person is short or long-sighted. For example the prescription written below demonstrates how the right eye (RE) is short sighted needing a simple minus lens (-2.25) to correct it; where as the left eye (LE) is longsighted requiring a simple positive lens (+3.75) to correct its refractive error. The lenses used in this case are called Spheres (spherical power). If you see a number written alone (as demonstrated below) this means that the eye is either long or short sighted and has no astigmatism. Prescription (RE): -2.25 (LE): +3.75 If an individual has an astigmatic element (rugby ball curve to their cornea); their glasses prescription will be a combination of more complex lenses (both positive and / or negative lenses). This longer more complicated prescription is needed to rectify/correct the amount of astigmatism. Vision Prescription VA 6/60 (RE): +4.50 / -3.00 x 180 6/18 The above prescription is of a right eye which is long sighted with astigmatism). The numbers relate to a +4.50 Spherical power lens to correct the spherical element, and the amount of astigmatism is corrected by a -3.00 (Cylindrical or Astigmatic power) lens, the axis of which is at 180 degrees. You will see that the person’s visual acuity in the previous case was improved with the glasses prescription. This person can see 6/18 (VA: visual acuity) with the above prescription, but could only see 6/60 (vision) without. Therefore although this individual may not reach the bottom line of the chart, they have achieved a good improvement in VA with the glasses. A copy of an up to date prescription is necessary in order to get new glasses. An example of a prescription can be seen on the yellow voucher given to you by the optometrist.
The power or strength of corrective lenses / glasses necessary. This is measured using refraction or a retinoscope. You may notice the optometrist sitting at arms length from the person in a dark room, using a piece of handheld equipment that produces a small streak of light; this is moved up and down / back and forth in front of each eye in turn; a combination of lenses (spheres and cylinders- see Prescription later) are put in front of this light to help determine the strength of the eye.
The retina is a complex delicate structure of the eye. It is the light sensitive tissue lining the inner surface of the eye. The optics (lens plus cornea) of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centers of the optic nerve. 2 A sharp image striking the retina generally results in a clear picture projected to the brain, any blur or misalignment of images result in a blurred and confusing message to the visual system. Any interruption or anomaly along the pathway to the brain will also result in an unclear / unusual visual image.
The ability to see in 3D. Some children may have poor depth perception and will perform poorly in stereopsis tests. This can be noted by parents when the child tries to perform daily tasks such as when trying to line up objects in games, or misjudging steps (i.e. lifting feet too high). Some children’s eyes can’t work together due to different reasons such as amblyopia (lazy eye) or a strabismus (squint) so therefore their depth perception (3D vision) is reduced. Quite often children will work around this and learn to use ‘monocular cues’ in order to judge distances etc. *Monocular cues: judging distances and depth perception with one eye i.e. if you suddenly become monocular (lose one eye) you are legally unable to drive for 6 months until you adjust to judging distances etc with one eye.
When one or both eyes turn in (Esotropia) or out (Exotropia). Both can be related to amblyopia / a lazy eye. Orthoptists specialise with strabismus treatment. Management can be a combination of things such as glasses, patching and possible surgery.
How well an individual can see, without glasses/corrective lenses.
Visual Acuity (VA)
How well an individual can see objects (letters/symbols) with glasses. This is measured during an eye test and is written as a figure called visual acuity (VA). The optometrist will assess what the child can see with and without glasses, often visual acuity (with glasses) is better than vision (without glasses). For example if your childs VA is 6/24; this means that the child needs to be 6 meters away from an object which you or a person with ‘normal vision’ can see at 24 metres). OR more simply if a child see’s 6/24 this means that an object needs to be 4 times larger or closer (6 divided into 24 goes 4 times, therefore 4 times larger) than something a person with ‘normal vision’ can see at an average distance. This rule can be applied to any of those 6 over figures i.e. 6/60 ..this means your child with a VA of 6/60 needs the object to be 10 x bigger or 10 x closer; than you / a person with ‘normal vision’ can see.
The extent of space in which objects are visible to an eye in a given position i.e. if you fixate on an object in this distance without moving your eye you are still able to see the surrounding landscape. This can be reduced in some individuals to almost a tunnel vision effect (like looking through cardboard tubes). Some children can bump into objects or not open their mouth when presented with a spoon from a certain angle because they have no vision in that area. A simple visual field assessment will be performed by your optometrist or ophthalmologist.
The visual acuity is still blurred / edges of objects are indistinct, or there is a loss of the visual field. Sight problems are very common, and many people are either long or short-sighted; however a visual impairment remains despite correction with glasses. Glasses can improve the vision a little, taking pressure off the visual system, and providing a clearer image. However as there may be structural changes or developmental damage to the eyes or visual pathway, the maximum level of visual acuity achieved from wearing the glasses, is not at the ‘normal/standard’ level of vision i.e. 6/6 is also known as “20:20 vision”.
Light passes from the eye, through the retinal photoreceptors (rod and cone cells), along the optic nerves to the brain, were the picture is received / deciphered. This corridor is called the visual pathway. Structural complications can occur at different parts along this pathway. Various tests help us pin-point why children may not be able to see as well as we would expect.