Welcome to question of the day #391

Eyetool question of the day #391

I’ve opened a new community eye care practice. Many of my patients are older and some have hand magnifiers that they have bought for themselves or that have been supplied by other eye care specialists. Nearly all of them use their hand magnifier with their reading segment or reading glasses. I remember reading somewhere that hand magnifiers work best with distance lenses. Can you advise?

For a person to get the optimum field of view and clarity all hand magnifiers should be used with the distance prescription if the person has need of one.

 When a hand magnifier is held at a distance from the near object that exactly matches the focal length of the lens in the magnifier the light emerging from the rear of the lens and moving toward the eye is parallel. It’s as if the light is coming from a long way away and not from a near object.

 Light that is parallel behaves as if it coming from the distance and therefore in order for it to be clearly focused on the retina the person needs to be using their distance prescription if they require one or no prescription if they are emmetropic or have a distance prescription that does not require refractive correction.

 Holding a hand magnifier at its focal length from the object of regard means it provides optimum clarity and field of view.

 Some eye specialists do not know this and advise their patients to use the hand magnifier with their reading prescription.

 Those patients who purchase their own hand magnifier use their reading prescription as they think because they are trying to read something with the magnifier they should be using their reading prescription.

 Using the reading prescription with a hand magnifier means that the field of view and clarity will be sub-optimum. Reading prescriptions are designed to focus with divergent emergent (from the magnifier lens) light and not parallel light.

 Advise your patients to use their distance prescription for reading with a hand magnifier. This is so important that if the patient has only bifocals or progressive lenses then recommend a pair of single-vision distance vision glasses for use with the hand magnifier and explain your reasons for doing so.

 Also advise them when using the hand magnifier to wear their distance glasses, place the magnifier on the page (or object of regard) and then move the magnifier towards them until the print or object of regard is clear.

 The closer they can get to the magnifier at the position of maximum clarity will help increase the field of view.

 This is how your patients will get the most out of their hand magnifier.