Displacement of optical centers in over-the-counter readers: a potential cause of diplopia.
Induced prism in spectacle lenses, which may result from inadvertent displacement of optical centers, may worsen an existing heterophoria or even cause diplopia, yet over-the-counter reading glasses (OTC readers) are not always assessed by clinicians when evaluating patients with diplopia or asthenopia. To gauge the magnitude of this potential problem, we used a focimeter and prescription aligner to assess the frequency and extent of clinically significant manufacturing variations in a random selection of 160 OTC readers. The optical centers were vertically displaced by ≥3 mm in 11%, with a maximum displacement of 7 mm in 1 pair. Average interpupillary distance was 64 mm (range, 58-74.5 mm), with interpupillary distance outside the normal range of 60-70 mm in 5%. Monocular pupillary distance was asymmetric by ≥5 mm in 4%. A 0.75 D power difference between lenses was measured in one pair of OTC readers. Some OTC readers have misaligned optical centers and other manufacturing defects that are of a magnitude sufficient to exacerbate a heterophoria and cause asthenopia or diplopia.
Pediatric Ophthalmology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Department of Ophthalmology, University of Cincinnati, Cincinnati.
Constance E
CE
West
Department of Ophthalmology, Boston Children's Hospital, Boston, Massachusetts; Department of Ophthalmology, Harvard Medical School, Boston. Electronic address: david.hunter@childrens.harvard.edu.
David G
DG
Hunter
D004172:Diplopia / Q000209:etiology*; D005139:Eyeglasses / Q000009:adverse effects*; D006801:Humans; D055095:Optics and Photonics