Introduction
The examination of vision is the most fundamental examination in ophthalmology. Regardless of what symptom the patient presents with, it must initially be established what the impact of this symptom is on the eyesight and how serious the implications are. In this section we will discuss the various aspects of this examination, using three symptoms relating to vision with which a patient may present. In addition, the history-taking for these symptoms will be covered in more detail.
The questions that are asked when taking the history originate from the so-called prediagnosis. Ask yourself, in connection with the hypothetical causes of the symptom, which other phenomena could occur.
When a patient presents with the symptom that they no longer see sharply, the cause of this may lie in the refractory media of the eye. It may concern refractive errors, or damage to or blurring of the refractory media resulting from one of the underlying causes emerging from the prediagnosis. In order to reach a first differentiation, when taking the history you need to ask:
- How old is the patient?
- How long have the problems existed?
- Did the problem develope suddenly or gradually?
- Are both eyes equally affected?
- Do the problems occur when looking into the distance, close by or both?
- Was there any trauma to the eye prior to the start of the problems?
- Does the patient have headaches, particularly after longer periods of looking close up (e.g. reading, craft work)?
- Do the patient’s symptoms increase when the light is at an angle of incidence and/or at dusk?
- Does the patient have a systemic disease (e.g. diabetes), an inherited disease (e.g. Marfan’s syndrome) or a chromosomal abnormality (e.g. Down syndrome)?
- Do the eye problems in question occur in the family?
The examination in adults
Required materials
To perform the examination of vision, the following materials are required:
- a visual acuity chart with adequate lighting
- a pointer
- cover spoon or cover patch
- a stenopeic opening (pin hole)
- white background chart
- reading card
- lenses +/- 1 diopter
The visual acuity chart and lighting
The visual acuity chart
For adults and children above the age of 4 to 5 years, various types of visual acuity charts are available. The most commonly used are:
- The Landolt ring chart
- The E chart
- The letter chart
For all charts the following should apply: the background is bright white and the symbols are deep black. In this manner, an optimal contrast between the symbols and background is achieved.
- The Landolt ring chart [Figure 1] is devised of rings that reduce in size per line, from which a segment has been deleted at the position of 12 o’clock, 3 o’clock, 6 o’clock or 9 o’clock. The size of the rings and measurements of this missing segment are determined by the Snellen principle. The patient has to indicate where the segment is missing; either at the top, bottom, right, or left.
Figure 1
- The E chart [Figure 2] consists of the capital letter E positioned either normally, vertically mirrored, lying on the long side of the E, or standing on the legs of the E. Again, the line for line size reductions of the symbols are determined by the Snellen principle. The patient has to indicate in which direction the legs of the E are pointed.
Figure 2
- To conclude, there is the letter chart. It consists of various capital letters placed in random order, which again reduce in size per line and their sizes are also determined by the Snellen principle. The patient has to identify the letter indicated by the examiner.
The advantage of the former two charts is that they can also be used when examining patients that are illiterate and children who are not yet able to read. Patients who struggle to identify right, left, up and down can indicate what they see by pointing with their fingers or to hold a demonstration ring or E in the same position as the symbol indicated by the examiner.
The visual acuity charts are produced for use with a patient at 5 to 6 metres away from the chart. Vision is determined by the ratio between the distance (d) at which the patient is examined (i.e. 5 or 6 metres away from the chart) and the distance (D) at which a person who has Snellen vision 1.0 is still able to read the line; d is the numerator in the ratio, and D the denominator. The obtained visual acuity is therefore a number without dimension and does not have any relation to the strength of the lens that is potentially used for correction.
Example: a patient can just about read the line at a distance of d=5 metres, whereas a person with Snellen vision 1.0 can still read this at a distance D=20 metres.
The vision of the patient equals 5m/20m = 5/20. On most visual acuity charts, this result is reduced to a decimal Figure and is therefore presented as 0.25.
Lighting
For the examination, one can use a transparent visual acuity chart that is placed in front of a light box [Figure 3]. In this way, an even, non-blinding level of light is achieved on the chart. An alternative is a non-transparent chart that is illuminated from light sources placed on either side of the chart. The latter solution means that the lights will have to be screened in such a way that the chart is illuminated but patients are not blinded. Fixing a spotlight to the ceiling, aimed at the chart is another good solution. In this particular case it is important that the light is not reflected by the chart. Homogenously, the measured light strength on the visual acuity chart should be 100 lux.
Figure 3
Pointer
To clearly indicate the symbols on the chart, it is important to have a pointer available [Figure 4]. As with the symbols, it is best for this to be black, to achieve a maximum contrast with the white background of the chart.
Figure 4
Cover spoon or ‘cover patch’
The examination of vision is performed separately for each eye. Therefore, a spoon
[Figure 5] or cover patch needs to be at hand to cover the eye that is not being examined. The disadvantage of the spoon is that it never completely covers the eye and the patient can still peek past the edges of it.
Figure 5
A cover patch consists of a type of blindfold in which an eye patch is opened up. The patch can be placed on front of the eyes and fixed using two bands of Velcro. By turning the patch around it can be applied to either eye. With this aid, sufficient cover of the non-examined eye can be guaranteed.
Finally, one can also apply a fitting pair of glasses [Figure 6] on which a cover [Figure 7A] is placed at the side of the non-examined eye. The quality of the covering is not as good as with a cover patch; by tilting the head, a patient will be able to look past the cover.
Figure 6
Figure 7
The least satisfactory option, certainly with children, is to allow the patient to cover the non-examined eye with their hand. By not closely holding the fingers together, ‘peek holes’ are created through which the patient can look. In addition, this will create the same effect as a stenopeic opening.
A stenopeic opening
This consists of a black plate with a small pinhole in the centre [Figure 7B]. Its use will be explained in the section on the examination technique.
White background chart
If a patient is not able to read the upper line of the visual acuity chart, one proceeds with the counting of fingers. For this, the fingers have to be held in front of a bright white background to obtain an optimal contrast.
Reading card
In order to examine a patient’s near vision one needs to have access to a reading card. On this, texts are printed that decrease in size, or in some cases, e.g. sheet music that decreases in size (the distance, at which musicians have to be able to read sheet music, differs from written text in terms of demand to the eye). The card is used with normal, sufficient lighting and at a distance where the patient in seated in a comfortable reading position.