Children/young adults can obtain relative distance magnification using accommodation, but adults can't do this
Microscope (MS) types
Standard spectacle lenses (single vision, bifocals)
Paired lenses (with base-in prism)
Clip-on bar-mounted or head-band mounted magnifiers
Advantages of microscopes
The PX has both hands free to hold, carry out, the special task
Large field-of-view compared to other devices of equivalent power. With practice, reading speeds are generally faster with microscopes than with other optical aids of the same power
Similar cosmetic appearance to regular glasses – spectacle frame of choice
Disadvantages of microscopes
Reduced working distance
The position of the head, neck, and arms may result in fatigue and postural discomfort
Task illumination difficult
The user must make arm movements rather than eye movements in order to scan text. This new relationship must be learned
May be heavy and physically constricting
Binocular spectacle magnification
Over the shelf prism high powered near addition could be successful
To achieve binocularity with spectacle magnification (custom-made MS), the optical centers of lenses should be coincident with the object's WD, achieved by decentration or adding base-in prism
Decentration
Half of the pupillary distance (PD) = (Back vertex distance (BVD) + Ocular radius (OR) + Working distance (WD) of object) / (BVD + OR)