Decompensated Phoria

An overview of decompensated phoria and its treatment.

Alex Christoff Orthoptist Assistant Professor of Ophthalmology The Wilmer Eye Institute at Johns Hopkins  Phoria is a “latent” tendency for the eyes to deviate  Controlled by fusion.  Normally, when open, the eyes are aligned.  No manifest deviation  Revealed by alternate occlusion (see the video) Exophoria in a healthy young adult female  Exophoria – Each eye moves in a temporal to nasal direction as it picks up fixation during alternate cover testing  Esophoria - Each eye moves in a nasal to temporal direction as it picks up fixation during alternate cover testing  Vertical phoria – One eye moves down (hyperphoria) and the contralateral eye moves up (hypophoria) during an alternate cover testing  Often symptomatic, chief complaint of acquired diplopia  Worse with fatigue  Worse at the end of the day  Or at specific fixation ranges, with driving, or with reading / frequent computer use  Usually intermittent, controlled by fusion  Not constant, as seen with nerve palsies and INO  Can be either horizontal or vertical  Typically small-angle  Comitance is the hallmark of decompensated phoria  Similar amplitude of deviation in all diagnostic gaze positions  Similar magnitude of strabismus measured at distance compared to near  Diplopia can develop if/when normal fusional convergence, divergence, or vertical vergence amplitudes are exceeded or impacted by trauma or neurological disease  Normal values of human fusional vergence amplitudes are shown in the table.  Relatively large for fusional convergence  Panum’s fusional space (single binocular vision , stereopsis) larger horizontally  Less so for fusional divergence  Exceedingly narrow for vertical vergence  Panum’s fusional space (single binocular vision , stereopsis) smaller horizontally  Why small hyperphorias can cause diplopia  Exophoria: X  Esophoria: E  Hyperphoria: RH/LH  Hypophoria: Rhypo/LHypo EPIC screen capture showing comitant exophoria in all diagnostic positions of gaze at distance, and at near fixation  Generally either temporary, Fresnel Press-On prism  Larger deviations can be corrected with light-weight prism on only one lens, over the non-dominant eye  Or permanent, ground-in spectacle prism.  Limited to about 7^ to 10^ per lens due to weight considerations and expense 15^ base out on the left  The goal is to give just enough prism to correct the manifest component of the strabismus, as obtained by simultaneous prism and cover testing (SPCT), allowing the patient’s residual fusional amplitudes to work to control the remainder of the fully dissociated deviation, obtained by prism and alternate cover testing (PACT).  Greater amounts of prism may act as a physiological crutch, exacerbating muscle length adaption and sarcomere loss / shortening, ultimately worsening the deviation in the long term  In essence, you are working WITH a patient’s innate ability to fuse, not substituting for it with prism  Quantifies the manifest component of a strabismic deviation  Basically an INSTANT neutralization of the manifest strabismus  Simultaneous application of corrective prism over the deviating eye  With occlusion of the fixating eye  Use trial and error until no shift is seen under the applied prism  Measures both manifest and latent components of an underlying strabismus with increased dissociation, further eroding fusion.  Tenacious proximal fusion may preclude FULL dissociation  Long term, Marlow style occlusion can be used to further enhance full dissociation  Prescribing Prism - American Academy of Ophthalmology Website Prescribing Prisms: Prescribing Prism (aao.org) – Accessed 4/13/22.  Razavi ME, Poor SSH, Daneshyar A. Normative values for the fusional amplitudes and the prevalence of heterophoria in adults. Iranian J of Ophthalmol. 2010; 22(3):41-46.  Reading, the Eyes, and Learning Disabilites, Knights Templar Eye Foundation – Pediatric Ophthalmology Education Center, American Academy of Ophthalmology Website. Reading, the Eyes, and Learning Disabilities - American Academy of Ophthalmology (aao.org) – Accessed 4/13/22  Palomo Álvarez, C., Puell, M.C., Sánchez–Ramos, C. et al. Normal values of distance heterophoria and fusional vergence ranges and effects of age. Graefe's Arch Clin Exp Ophthalmo 2006 244, 821–824  von Noorden GK, Campos, EC. Binocular vision and space perception in: Binocular Vision and Ocular Motility. Theory and Management of Strabismus. 6th Edition. St. Louis: CV Mosby Co; 2002. pp. 16-20.  Palmisano S, Gillam B, Govan DG, Allison RS, Harris JM. Stereoscopic perception of real depths at large distances. Journal of Vision, 10(6):19, 1–16.  Guyton DL. The 10th Bielschowsky Lecture. Changes in strabismus over time: the roles of vergence tonus and muscle length adaptation. Binocul Vis Strabismus Q. 2006;21(2):81-92. PMID: 16792523  Marlow FW. THE PROLONGED OCCLUSION TEST. Br J Ophthalmol. 1930 Sep;14(8):385-93. doi: 10.1136/bjo.14.8.385. PMID: 18168889; PMCID: PMC511207