Magnifiers create an image at a specific distance from the eye. The eye must accommodate to this distance. If the eye can no longer accommodate sufficiently for the image at this distance, reading glasses should be used for the distance between the eye and the image created by the magnifier. If the eye cannot accommodate or if the reading glasses are “not right”, it is not possible to see clearly with a magnifier. Reading stands offer a constant distance between reading material and the eye. The majority of magnifier manufacturers provide the necessary data to test reading glasses with the relevant magnifier.
To find the right spectacles, the following requirements should be observed:
The virtual image created by lower power magnifiers lies between 10 and 20 cm below the reading material. The patient must either accommodate to this distance or the spectacles must be adjusted to it. Reading spectacles can only be used at a reduced distance. Distance spectacles are usually also not suitable. Progressive lenses enable the wearer to use the magnifier in an ergonomic posture thanks to the progressive lens zones, provided the progression channel is wide enough.
The best solution consists of an extra pair of single vision lenses fitted with a medium addition that have been adjusted to ensure a relaxed posture when using the magnifier. Standard reading spectacles with an addition of 3.0 D or 3.5 D would be too strong for use with a magnifier. The plus power for the “magnifier addition” normally ranges between +1.0 D and +2.0 D. Eyeglasses in this power are also often used as a visual aid for intermediate distances (e.g. household tasks). Higher power magnifiers (6x and above) can only be used at a relatively short distance from the eye. Visually impaired people find the right distance easily themselves. However, comfortable reading at a table is no longer possible. The use of an additional reading stand is advisable.
It is important to ensure that presbyopic patients using (illuminated) hand magnifiers can actually see the virtual image created by the magnifier at a specific distance clearly with their spectacles. Presbyopic patients usually wear reading glasses for near vision. These glasses only provide sharp vision in a relatively short distance range. The virtual image created by a magnifier is formed at a specific distance from the magnifier and consequently at a specific distance from the user’s eye. Presbyopic patients with near vision glasses can only see the virtual image clearly if it is formed at the near point of the near vision lenses.
By changing the magnifier-to-object distance, the distance of the virtual image created by an (illuminated) hand magnifier can be adjusted so that it lies within the near point distance of the eyeglasses. Presbyopic patients usually have no problem with this since they intuitively find the right distance to see the image clearly.
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