moochy

Oh my head hurts....

my goodness i miss having coloured hair

i want pink hair again, and to go a bit mad somedays....but i guess my patient's might get a bit weirded out by it?


I wrote this essay, its so dull.....


OPD1013 Visual Optics:
Vision and the visual system.

The measurement of visual acuity in a five year old child,


Poor vision in children can be associated with under development. .It is important to establish how well the child's vision, speech, communication, hearing and coordination have developed. Asking about family history and any symptoms noticed by family members, for example eyes turning inwards is useful. {fig 1.1}
There are a selection of methods available for measuring visual acuity in children. The method of choice depends on the patient's age, development and understanding.
At birth on average a child's visual acuity is lower than 6/60 {see def.1.0}. This gradually increases to 6/15 after one year and 6/6 by five years.

The following are some examples of currently available methods of measuring visual acuity in a five year old.

Snellen testing chart, {see fig.1.2}

This is the most commonly used method of testing visual acuity in adults and can be used for literate children. The child sits 6 metres from the chart, which has rows of black letters on a white background. The lines start at 6/60 [large] to 6/4 [small]. The patient is asked to start at the top letter and read down each row of letters until they cannot read them anymore. The practitioner records the level they achieve.


Letter Matching or Sheridan Gardiner test, {fig 1.3 and 1.4}

The Sheridan Gardiner test is popular among practitioners when testing pre-school children; this is because it is portable, easy to handle and to present to a child. The practitioner holds a card with one letter on at six metres from the child. The letters vary in size from large [6/60] to very small [6/6]. The child then matches the letter presented with one on a key card that they hold.
The Kay picture test is similar; and is ideal for young children. Instead of letters it pictures. They also go from large [6/60] to small [6/6] sizes.
Both of these tests can also be performed at three metres.
The disadvantage is that the measured acuity tends to be slightly higher than with Sheridan Gardiner; because there is no crowding effect.


Landolt ring and Illiterate E test types. {see fig 1.5 and 1.6}

This method of testing visual acuity is very similar to the Snellen chart, except it uses rotated E's and C's. It is very useful for children who do not know their alphabet yet as all they have to do is point the direction that the letter is facing. Again, like the Snellen chart the letters decrease in size as you go down the rows. The test is taken at a distance of 6 or 3 metres from the patient. If the patient struggles with the direction of which the letters are facing [e.g. left and right] they can have a smaller hand held letter to rotate to the correct direction.

The following two tests tend to be used with very young children, and also in research and with people with learning difficulties.

Optokinetic Drum test, {see fig. 1.7}

This is mainly used for children under the age of two, but can still be used with under developed five-year olds. This test uses a black and white striped drum, which is rotated in front of the child's eyes. Unlike other tests, the drum is held near to the patient's eyes, but different types of stripes are used to determine different levels of visual acuity. The practitioner observes eye movements which show tracking when the target can be seen by the patient. This is called Optokinetic nystagmus.


Preferential Viewing test, {See fig 1.8 and 1.9}

Preferential viewing is a method that is used to measure both the visual acuity and contrast sensitivity in children from birth to about five years of age. There are several methods of preferential viewing, an example being the Cardiff Acuity Test. A child is shown a card with a picture in one half, and a blank space in the other half. If the child can see the picture it will look at it. The child can either point to the picture, identify it or in very young children just the point of gaze is observed, the practitioner must note whether the child was looking at the picture or the blank space.

The different test methods will give slight variations in acuity measurements. This does not matter hugely provided that when monitoring a child's visual development the same method is used for comparison at subsequent visits.













Appendices.

Definitions:

1.0.


Figures:
[attached]

References:

1. Introduction to Visual Optics, Alan H. Tunnacliffe, 4th edition, published 1993.

2. Notes from OPD1013, Visual Optics, Vision and the visual system 2006.