How to prescribe spectacles for presbyopia
Spectacles for near vision can help a person see clearly for tasks such as sewing, carving or reading. This step considers how to prescribe spectacles for blurred near vision, or presbyopia. This article is adapted from: du Toit, R. How to prescribe spectacles for presbyopia. Comm Eye Health. Vol. 19 No. 57 2006 pp 12 - 13.
As we grow older, the lens loses the ability to focus at close distances. Starting around the age of 40, near vision slowly becomes worse, but distance vision is not affected. People with presbyopia usually say that their near vision has slowly become worse.
- Distance and near vision charts
- Pinhole (optional)
- A trial set of lenses or a selection of ready-made spectacles. See Table 1 for suggested powers.
Table 1. Suggested lens powers for correction of presbyopia.
- Before you start: make sure there is nothing else wrong with the person’s eyes, measure the person’s distance vision and ask about their health. Several diseases pose related eye problems.
- Take a detailed history. Write down the person’s age and medical history and symptoms.
- Find out the person’s working distance: that is the distance at which they would like to do most of their near work. (See Figure 1).
Measure near vision: the person holds the near chart at their working distance with both eyes open. Ask them to read the smallest line or demonstrate the smallest shapes they can see clearly.
- Identify the correct lens power
* Look up the person’s age in Table 2 and select the power to try first.
* Measure near vision with the selected power spectacles or trial lenses. Give the person the near chart to hold at the distance they would like to see clearly. Ask him or her to show the smallest line they can see. If the person cannot see at least the N8 line (newsprint size) try the next stronger power.
* Check the range of clear vision by trying out the testing at various distances. Ask the person to look at the smallest line they can see on the near chart and then bring the chart closer until the letters become blurred. Hold one hand to mark the closest distance (see Figure 2a), then ask the person to move the chart further away until the letters become blurred. Mark the furthest distance (Figure 2b).
* Ask the person to hold the chart at the distance they want to see clearly. This is the working distance. If the range is correct, the working distance should be in the middle of this range, for example at about 40 cm (Figure 2c). This means that a person will be able to see clearly for the same distance in front and behind their working distance.
* The power is correct if the middle point of the range is the same as the working distance. Keep testing the range until the power is correct. Write down the power of the lenses and the near visual acuity with these lenses.
* If the person cannot read N10 on the near vision chart with any power lenses, they need further eye checks.
Figure 1. Woman demonstrates her working distance, and Figure 2a-c Checking the range of clear vision. Victoria Francis/ICEH.
- Before prescribing spectacles, note:
* Approximate lens powers, based on age, will not be suitable for all. For example, a lens power stronger than expected for the person’s age may be needed if the person has hyperopia (far-sightedness), low vision, wants to work at a distance closer than 40 cm, or to see very small objects.
* Do not prescribe a power that is too high because then the person will have to hold things too close to their eyes.
* A change in spectacles is usually only necessary if the person needs at least 0.50 stronger than their old spectacles, has received spectacles for presbyopia about two years ago, or can see better with the new spectacles than their old spectacles.
- Select the type of lenses that would be best for the person. Table 3 describes the options.
- Adjust the spectacles to fit properly and feel comfortable. Explain the use of spectacles for presbyopia and how to look after them.
- Remind them to return in about two years to check if they need new spectacles to see more clearly at close distances.
Table 2. Suggested lens power for different ages
|Person's age||Lens power|
|Over 55 years||+2.50 or higher|
Table 3. Types of lenses
|Type of lenses||Advantages||Disadvantages|
|Single vision (ready-made, near or reading spectacles)||Less expensive||The person will see clearly at near but their distance vision will be blurred when they look up|
|Bifocal lenses and multifocal lenses||Useful if a person has a distance refractive error and presbyopia, or if they need to see clearly at distance and near||Usually more expensive than single vision spectacles for presbyopia, and may take longer to acquire|
What are the different outlets for presbyopia spectacles in your setting? What are the practical concerns on acceptability, accessibility and availability of presbyopic correction, within your own setting? Post your thoughts in the comments area.