In part 1, I covered longsightedness, shortsightedness, astigmatism, squints, lazy eyes and why its important for your child to have a full eye examination rather than relying on the nursery screening programme. In this part I will explain some other aspects of your child’s vision.
Anisometropia is where the lens power required is very different in each eye. Children with Anisometropia don’t know they have a problem. The situation is a bit like having a short leg and a long leg. You can use the long leg or you can use the short leg but you can’t use them together. Let me use the example of a child who is a bit short sighted in one eye and longsighted in the other. They could see distance objects clearly with the longsighted eye and near objects clearly with the shortsighted eye. This child will not be aware of any problems but could have issues with the development of the visual system that deals with the two eyes work together (Binocular Vision). Anisometropia is responsible for problems with image size differences and it is one of the causes of lazy eyes (Amblyopia).
We all know children that excel at sports. Whether it’s football, badminton, netball or table tennis, these kids have got it nailed. We also know kids that couldn’t catch a tennis ball even if their life depended on it. So what’s the difference between these two groups of children. The main difference is often to do with their eyes and whether the have good stereopsis (3D vision). Although both eyes look in the same direction the viewing position of each eye is slightly different. The distance between the eyes is generally between 48 and 74 mm. As the visual system develops it learns to interpret the very slight differences in the images from each position as 3D vision. If your child has an issue, which stops the normal development of their visual system, they will have poor or no stereopsis. Without good stereopsis a child would be unable to judge how far away the tennis ball is, and would have difficulty catching it. If your child has difficulties catching a ball an eye test would be a good idea.
If you would like to experience what it is like to have no stereopsis try playing a game of catch with one eye covered.
Diplopia (Double Vision), needs to be investigated by an optometrist. The chances are high that your child will tell you they have double vision but some may not.
There are two types of diplopia. The first is when things are double when you look in one direction but not in others. Either something has damaged one of the ocular muscles that control the movement of the eyes or something has happened to the nerve that controls the muscle. A forceps delivery can result in this type of problem. Patients with this type of double vision will turn their head to the side to minimise effect of the diplopia.
The second type is when the diplopia is in all directions of gaze. This occurs because the eyes are not looking in the same direction ie a squint. If untreated the brain will do one of two things. It will either disregard the image from one of the eyes, which will result in the development of a Lazy Eye or split the visual system in two so that each eye can see independently but not together.
If found early enough treatment can ensure that each eye has good sight and the visual system develops with both eyes working together.
Patients often get confused about double vision. If you see two distinctly separate images of the same thing with almost equal clarity you have diplopia. The images can be side-by-side or one above the other. Diplopia occurs when both eyes are open. If you close one eye you will only see one image. If you look at something and see a ghost image of the same thing, which almost entity overlaps the first image it’s probably blurred vision and spectacles should sharpen up the image.
Nothing surprises a parent more than discovering that their child has a colour vision problem. The main reason for this is a lack of understanding of what the phrase “colour blind” means. People often assume that patients who are “colour blind” have black and white vision. The phrase “colour defective” is much more appropriate. Colour vision can be explained by comparing it to the computer screens. The first colour screens used 16 colours and the more modern screens have 256 colours. Colour defective patients are like the 16 colour version. They can see colours but lack the range of colours that everyone else can see and they may confuse lime green with lilac. Some patients have minor colour vision issues while others had more significant issues.
There is no treatment for colour vision problems, which are predominantly hereditary. About 90% of patients with colour vision issued are male and they pass the gene through their daughter to their male grandchildren.
The detection of colour defective patients by optometrist is essential to make sure that they choose a career that does not require good colour vision.
The pupil is the black hole in the middle of the coloured part of the eye (Iris). It gets bigger or smaller depending of the amount of light entering the eye. There are a couple of pupil problems that parents are not likely to notice. A difference in pupil size can be an indication of a problem and should be investigated. This sometimes occurs after the patient has been suffering from a viral condition. Small pupils could be due to exposure to certain substances and should also be investigated.
If your child bumps into things a lot more than their peers there may be an underlying cause. There are of course many reasons why children bump into things. Telling them that they should look where they are going may if the problem is just carelessness. It may however be because of issues with their peripheral vision. The big problem with peripheral vision is that you can’t see what you can’t see. If you have an area of your peripheral vision that is blind it doesn’t appear black. It just doesn’t appear. So you don’t know it is missing. A good way to demonstrate this is to use a pen. Cover your left eye and pick an object to focus on. Stretch out your arm in front of you with the pen. Place the top of the pen just to the right of the object you are looking at. Slowly move the pen about 6 or 7 inches to the right while watching the object. The top of the pen will disappear. You have just placed the pen in the blind spot created by your optic nerve and you didn’t know it was there.
You child will not be able to tell you that they have a problem either. Reduced visual fields could have a variety of causes, including genetic conditions, congenital problems, cerebral palsy, trauma and neurological issues. If you have any concerns about this get it checked out.
Dyslexic children struggle with reading and writing. We have had children brought in for their first eye test, where the parents tell me that their child is dyslexic. Many attend learning support where they are taught useful strategies to help them cope at school. School can also allow extra time for exams, and other additional facilities. There are numerous specialist clinics that assess whether coloured overlays would help a child. Unfortunately they never thought that part of the problem might be that their child needed glasses. If you think that your child might be dyslexic get their eyes tested first. It is important to have good balanced vision without any eyestrain, as a starting point for a with child with potential processing issues.
I have had a patient bring in special coloured lenses (to assist him with his dyslexia) to be glazed into a frame. The assessment clinic had spent a lot of time refining the colour to maximise this teenager’s ability to read. The specialist lenses had and expensive tint but no optical power. I spoke to the parents and discovered that the teenager had never had his eyes tested. We tested his eyes and found that he required spectacles to correct a significant amount of astigmatism. We provided the clinic with the correct power of lens and they sent us a set of the tinted lenses with the astigmatic correction.
While I encourage all parents to take advantage of everything that is available for dyslexic patients at school, further education and in the workplace, it is important to remember that regular eye tests to ensure that the patient has good balanced vision without any eyestrain is the foundation upon which everything else rests.