Volume 18 Number 1 / February 2014 References 1. Mozayeni RM, Lam S. Phlyctenular keratoconjunctivitis and marginal staphylococcal keratitis. In: Krachmer JH, Mannis MJ, Holland EJ, eds. Cornea: Fundamentals, Diagnosis and Management. Philadelphia, PA: Elsevier Mosby; 2005. p. 1235-40. 2. Nichols JJ, Berntsen DA, Mitchell GL, Nichols KK. An assessment of grading scales for meibography images. Cornea 2005;24:382-8.

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3. Arita R, Itoh K, Maeda S, Maeda K, Amano S. A newly developed noninvasive and mobile pen-shaped meibography system. Cornea 2013;34:242-7. 4. Arita R, Itoh K, Inoue K, Amano S. Noncontact infrared meibography to document age-related changes of the meibomian glands in a normal population. Ophthalmology 2008;115:911-15.

Magnetic prism alignment system for measuring large-angle strabismus John Edward Bishop, MD

Prismatic measurement of large-angle strabismus requires the simultaneous use of two or more prisms for neutralization. To facilitate the clinical measurement of large-angle strabismus a new prism system was designed utilizing a flat plate and a ferrous metal surface coupled with prisms containing rare earth magnets implanted in their base and bottom surfaces.

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oose plastic prisms for ophthalmic use are available in assorted powers up to 50D. Although calibrated for the position of minimum deviation, they are generally positioned with the posterior face of the prism in the frontal (coronal) plane of the head.1 Thompson and Guyton have suggested nasally rotating the prism for measurement at near.2 Strabismus deviations larger than 50D require the use of two prisms. These cannot be held in the same direction in front of one eye because the powers are not additive and measurement errors result. Large deviations are better measured by dividing the estimated prism strength between the two eyes and holding each prism in the frontal plane.1 Although this examination technique has been found to minimize measurement errors, mechanical difficulties can arise when trying to simultaneously hold separate prisms in front of each eye in the frontal position. Proper positioning may be difficult in patients with a large interpupillary distance (especially in patients with exotropia, where the effective interpupillary distance at the prism

Author affiliations: Driscoll Children’s Hospital, Corpus Christi, Texas Gulden Ophthalmics (Elkins Park, PA) has a United States patent pending covering the use of prisms with a single magnet to which a magnetic stick can be attached. Submitted June 22, 2013. Revision accepted September 26, 2013. Correspondence: John Edward Bishop, MD, 4707 Everhart #108, Corpus Christi, Texas 78411 (email: [email protected]). J AAPOS 2014;18:101-102. Copyright Ó 2014 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/$36.00 http://dx.doi.org/10.1016/j.jaapos.2013.09.016

Journal of AAPOS

plane is increased), for examiners with small hands, or when it is also necessary to combine a vertical prism with the two horizontal prisms. Inadvertent rotation of one or both prisms about the vertical axis (the Z axis of Fick) induces a corresponding change in the effective horizontal prism power, while inadvertent rotation of one or both prisms about the horizontal axis in the sagittal plane (the Y axis of Fick) can induce a vertical prismatic error. Recently, Gulden Ophthalmics (Elkins Park, PA) introduced a standard loose ophthalmic prism set with rare earth magnets implanted in the bottom face of each prism. This patent pending system is designed for use with a magnetic stick so that an individual prism can be held in front of one eye. This prism set was modified by implanting a second magnet in the base of prisms up to and including 20D and by the addition of a flat plate with a ferrous metal surface. This magnetic prism system allows two horizontal prisms to be simultaneously positioned properly with one prism in front of each eye held securely in place on the metal plate by magnetic attraction. The prisms can be spaced for the patient’s interpupillary distance and can be adjusted to keep each in the frontal plane position for distance measurements or nasally rotated for near measurements (Figure 1A-B). The prisms can be freely rotated on the plate to keep the posterior prism surface in the frontal plane when measuring deviations in right or left gaze (Figure 1C). Each prism is held level by the plate avoiding induced vertical prism. When necessary, an additional prism with power up to 20D containing a magnet in the base can be positioned base down in front of either horizontal prism to neutralize combined horizontal and vertical deviations (Figure 1D). The plate with prisms combination can be easily held in front of the patient with a single examiner’s hand, keeping the other hand free to do alternate cross cover testing to confirm neutralization of the strabismus deviation (Figure 2). This magnetic prism system facilitates more efficient measurement of large-angle horizontal strabismus with or without superimposed vertical strabismus.

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FIG 2. Alternate cross cover testing with plate and prism device. References 1. Thompson JT, Guyton DL. Ophthalmic prisms, measurement errors and how to minimize them. Ophthalmology 1983;90:204-10. 2. Thompson JT, Guyton DL. Ophthalmic prisms, deviant behavior at near. Ophthalmology 1985;92:684-90.

FIG 1. Plate and magnetic prisms positioned for patient measurement. A, Two base-out prisms correctly positioned in the frontal plane for distance measurement, magnetically attached to plate. B, Two base-in prisms positioned in 5 of nasal rotation for near measurement, magnetically attached to plate. C, Head, plate, and prisms positioned for measurement in right gaze. D, Same as B, with addition of base-down prism before right eye.

Journal of AAPOS

Magnetic prism alignment system for measuring large-angle strabismus.

Prismatic measurement of large-angle strabismus requires the simultaneous use of two or more prisms for neutralization. To facilitate the clinical mea...
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