Hard to believe that it’s thirty six years (yikes!) since I authored an article for the journal of the American Optometric Association titled Telescopic Acuity in Amblyopia. The impetus for that article originated from interactions with the Feinbloom Center of The Eye Institute a few years earlier. Dr. William Feinbloom was convinced that patients with organic amblyopia due to disease had a functional overlay, particularly when the disease entity was quiescent. This resulted not only in compensatory magnification enabling better acuity through his spectacle mounted telescope, but a gradual improvement in visual acuity without the telescope in place providing a therapeutic benefit. With master’s and Ph.D. degrees in biophysics and visual psychology from Columbia University, I took whatever Feinbloom said seriously.
It has long been recognized that a diagnostic sign of functional amblyopia is an improvement in visual acuity beyond the magnification power of the telescope. In other words, a patient with 20/100 acuity would be expected to obtain 20/40 acuity when focusing through a 2.5x telescope. Improvement beyond 20/40 not only indicates functional amblyopia, but is a reasonably good indicator of what to expect as an endpoint acuity after therapy. In analyzing why the use of a telescope should have a functional and therapeutic effect, Feinbloom suggested that magnification accentuated central vision, and placed a premium on the stabilization of eye movements in order to localize and study the visual scene.
Bernell still distributes the Selsi hand-held monocular telescope that would be ideal for therapy activities. Beyond the original 2.5x model, powers are also available in 4x, 6x, 8x, 10x, and 15x. The higher the degree of magnification, the greater the need for steady fixation or the negative consequences of unsteady fixation when localizing points of regard.
Although I gravitated away from using the hand-held monocular telescope for therapy, it may be an opportune time to resurrect its use in amblyopia for two compelling reasons:
1) Research has shown that patients with amblyopia have deficits in perception of images in real world scenes. Active exploration with the telescope is not only fun, but is well suited for real world scenes or natural viewing.
2) Rather than occluding one eye, focusing with the telescope through the amblyopic eye while the fellow eye is open is a form of MFBF that is more compatible with the newer trends in treatment that “ditch the patch” while both eyes are open.