(Yoked) Prism Research

Cheng D, Schmid K, Woo G, Drobe B  "Randomized Trial of Effect of Bifocal and Prismatic Bifocal Spectacles on Myopic Progression."  Arch Ophthalmol. 2010;128(1):12-19.  
   Objective:  To determine whether bifocal and prismatic bifocal spectacles could control myopia in children with high rates of myopic progression. 
   Methods: This was a randomized controlled clinical trial. One hundred thirty-five (73 girls and 62 boys) myopic Chinese Canadian children (myopia of 1.00 diopters [D]) with myopic progression of at least 0.50 D in the preceding year were randomly assigned to 1 of 3 treatments: (1) single-vision lenses (n = 41), (2) +1.50-D executive bifocals (n = 48), or (3) +1.50-D executive bifocals with a 3prism diopters base-in prism in the near segment of each lens (n = 46). 
   Main Outcome Measures: Myopic progression measured by an automated refractor under cycloplegia and increase in axial length (secondary) measured by ultrasonography at 6-month intervals for 24 months. Only the data of the right eye were used. 
   Results:  Of the 135 children (mean age, 10.29 years [SE, 0.15 years]; mean visual acuity, 3.08 D [SE, 0.10 D]), 131 (97%) completed the trial after 24 months. Myopic progression averaged 1.55 D (SE, 0.12 D) for those who wore single-vision lenses, 0.96 D (SE, 0.09 D) for those who wore bifocals, and 0.70 D (SE, 0.10 D) for those who wore prismatic bifocals. Axial length increased an average of 0.62 mm (SE, 0.04 mm), 0.41 mm (SE, 0.04 mm), and 0.41 mm (SE, 0.05 mm), respectively. The treatment effect of bifocals (0.59 D) and prismatic bifocals (0.85 D) was significant (P < .001) and both bifocal groups had less axial elongation (0.21 mm) than the single-vision lens group (P < .001). 
   Conclusions:  Bifocal lenses can moderately slow myopic progression in children with high rates of progression after 24 months.

Fischer V,  Mahaphon T.  "Use of Yoked Prism in the Management of Nystagmus in Spina Bifida"
Optometry - Journal of the American Optometric Association June 2006 (Vol. 77, Issue 6, Pages 275-276)
   Background: Spina bifida, incomplete closure of the spine protecting the neural tube during the first 28 days of pregnancy, affects 1 in every 1,000 pregnancies in the United States. It most commonly affects the lower part of the spinal cord, with loss of motor control below the abnormality and secondary bladder, kidney, and central nervous system function. Hydrocephalus occurs in 80% to 90% of patients with spina bifida, requiring a cerebrospinal fluid (CSF) shunt to drain excess fluid from the brain. Ocular and neurological signs and symptoms of a shunt failure include head enlargement, headaches, nausea, vomiting, strabismus, diplopia, restricted eye movements, blurry vision, papilledema, visual-field defects, and abnormal pupil reaction.
Nystagmus is present in about 48% of patients with spina bifida.
   Case Report: A 14-year-old boy with spina bifida and a CSF shunt was brought to us with the chief symptom of decreased vision and neck pain secondary to his head turn. He was diagnosed with pendular congenital nystagmus with medium amplitude and frequency that dampened in right gaze, and a long-standing alternating 10^ esotropia. Cycloplegic refraction yielded 2.00 O.D. and 2.50 O.S. He was given 8^ Base Left yoked prism to alleviate his head turn and 1.25 sphere OU for his hyperopia. Uncorrected
distance vision without head turn was improved from 20/50 OU to 20/302, and near acuity was improved from 20/100 OU to 20/40. The magnitude of the head turn was greatly reduced.
   Conclusions: Management of patients with spina bifida should include possible yoked prism to dampen the nystagmus and improve visual function. Due to the life-threatening nature of CSF ventricular shunt failure, ocular signs and symptoms need to be closely assessed, especially the optic nerve head for papilledema.  


Galbrecht, O.D. D., Marks, O.D. L. and Franzel, O.D. A. "Successful Prism Treatment in Two Cases of Isolated Oculomotor Nerve Palsy"  Optometry - Journal of the American Optometric Association
June 2007 (Vol. 78, Issue 6, Page 271)
   Background: An oculomotor (third cranial nerve) palsy results from damage to the oculomotor nerve anywhere along its course in the brain. Both congenital and acquired forms can be total or partial, causing variances of pupil, eyelid, and extraocular muscle abnormalities. Ocular motility is drastically affected by oculomotor nerve palsies with limitation of elevation, depression, and adduction.
   Case Reports: We compared diagnosis and treatment of 2 adult females with long-standing oculomotor nerve palsies; 1 acquired and 1 congenital. The acquired-onset patient had been in a motor vehicle accident 41 years prior. She was suffering from diplopia that was reduced by tilting her head. The head tilt led to torticollis and eventually caused gradually worsening neck pain. The patient with congenital oculomotor palsy did not experience diplopia but had rather unusual episodes of visual disturbance accompanying eye pain and headaches. She had cyclical spasms, whereby the magnitudes of her ptosis and eye turn were variable throughout the day. Gradual worsening of her symptoms had prompted her to seek treatment.
   Conclusion: Although these patients exhibited vastly different symptoms, both experienced relief by incorporating yoked prism into their spectacles. Moderate amounts of yoked prism were used to eliminate diplopia and lessen the head tilt in the case of the acquired third nerve palsy. Small amounts of yoked prism and limited vision therapy reestablished an appropriate visual-spatial projection in the case of the congenital third nerve palsy. The patient experienced considerable relief from her visual disturbances and ocular pain.

Gizzi M, Khattar V, Eckert A "A Quantitative Study of Postural Shifts Induced by Yoked Prisms."  J Opt Vis Devel, 1997(28) #4, 200-203
    Spatial neglect occurs in patients with neurological deficits such as stroke, traumatic brain injury, and multiple sclerosis.  This neglect of the contralateral half of visual space may be accompanied by a shift of the center of gravity toward the intact hemi-field.  Yoked prisms have been used to correct the shift caused by neglect.  We used moving platform posturography to study subjects with normal vision before and after they wore yoked prisms.  An approximate 0.75 degree shift in the center of gravity toward the prism base was observed.  This amount of shift in subjects with normal vision is quite small.  Nevertheless, the results suggest that there could be a partial compensation for spatial neglect using yoked prisms.


Lazarus SM "The Use of Yoked Base-Up and Base-In Prism for Reducing Eye Strain At the Computer." J Am Optom Assoc, 1996(67) 204-208
    Eye strain continues to be one of the chief complaints of people working at video display terminals.  The increase in extorsion observed on elevation of gaze at near point may induce binocular disruption and strain.  Binocular base-up and base-in prism might mitigate some of the visual complaints of computer users because they decrease the elevation and convergence required.  A double blind study of 30 computer users indicates a significantly greater preference for a lens combining prism and plus power than for plus lenses having no prism.


Leslie S  "Optometric Management of Persistent Streff Syndrome with Vertical Yoked Prisms." Behav Aspects Vision Care, 2001 (42) #1 33-42
    Current optometric treatment of the condition known as Streff syndrome usually involves prescription of low plus lenses, vision therapy and counseling.  Most cases respond quickly to treatment and return to normal visual levels, but occasionally patients continue to experience significant visual performance problems while still demonstrating subnormal acuities and other clinical measurements of visual performance.  In the three cases presented, yoked prisms bases-up were successful in achieving a return to normal acuities when low plus lenses and vision therapy were only partially successful and suggest the need for other clinicians to consider yoked prisms as  a possible tool in the the treatment of Streff syndrome.


Richer SP, Hall T  "Mobility Spectacles for a Patient with Ankylosing Spondylitis.Amer J Optom & Phy Optics 1986 (63) #11, 927-930.
    A patient with severe postural deformity and mobility difficulties due to ankylosing spondylitis benefits from specially designed rimless spectacles incorporating yoked fresnel base-down prisms.


Sheedy JE, Parsons SD "Vertical Yoked Prism - Patient Acceptance and Postural Adjustment.Ophthal. Physiol. Opt.,  1987 (7) #1, 255-257
    Vertical yoked prism is sometimes incorporated in multifocal lenses to obtain a thinner lens, or prescribed for oculomotor deficiencies, or occurs if the vertical placement of spectacle lenses before the eyes is inappropropriate.  Patient acceptance of and postural and perceptual adaptation to such prism were studied.  Subjects could not significantly differentiate between 2 prism diopters base down and 0.  There was a nearly unanimous rejection of 4 prism diopters base down.  Postural changes were significant during 4 prism diopter wear but not during 2 prism diopter wear.  The results suggest that 2 prism diopter may be accepted by most patient, but 4 prism diopter will not.


Weissberg E, Lyons SA, Richman JE  "Fixation Dysfunction With Intermittent Saccadic Intrusions Managed by Yoked Prisms: A Case Report."  Optometry 2000 (71) #3 183-188
    Background: A 44-year-old woman came to us with a chief symptom of "jumping letters side-to-side, which is most noticeable while reading".  The onset occurred after she had experienced a closed head traumatic brain injury 3 years earlier.  Several neuo-ophthalmologists diagnosed a fixation instability secondary to saccadic intrusions and prescribed Gabapentin, which provided minimal relief.
    Methods:  The term saccadic intrusion refers to an inappropriate saccade with a disruption effect on fixation.  Our examination revealed a myopic anisometropia.  Motility testing confirmed saccadic intrusions that lessened on occlusion of either eye and superior gaze.  A plano spectacle with six prism diopter yoked base down was used to position the eyes in the superior null point.  Electrooculography, using the Visagraph II, demonstrated pre and post changes with the prism.  The uncorrected anisometropia allowed the patient to be monocular under binocular viewing conditions.
    Case Report:  The case report focuses on fixational problems that may occur secondary to traumatic brain injuries.  There is evidence that the origin of the problem may be from uninhibited brain stem circuits.  Pharmacological treatment may only offer transient improvement.  The responsibility of a functional cure is often placed on the optometrist.
    Conclusion:  This case demonstrates how an alternative use of prism
and prescription application can play an important role in the management of fixation dysfunctions.