Utilizing Prism in Primary Care Practice Sandra M. Fox, OD South Texas Veterans Health Care System Polytrauma Rehabilitation Center at San Antonio [email protected] Disclosure Statement: Nothing to disclose FUN WITH PRISMS! WHY DO WE LOVE PRISMS? Since a prism can shift images, it is a very useful tool in optometry where we have a need to shift images so people no longer see double or can more easily be aware of objects in their peripheral vision. FRESNEL PRISM • Press on prism • A piece of plastic with diffraction rings that give it a prismatic effect. • Has a base and an apex and works just like a “real” prism. • Available in 1 – 10 diopters in 1 diopter increments, 12,15, 20, 25, 30, 35 and 40 diopters. • Costs ~ $25 • The greater the power, the more it blurs the vision. • It is usually applied to the back surface of the lens in the glasses. FRESNEL LENSES FRESNEL PRISM ADVANTAGES • Allows us to trial prism before ordering glasses with prism ground in (costly). • Can be used in very high powers when a conventional prism would be too thick. • Can continue to change the power as the diplopia 2/2 CN palsies improves with time. • The blurring effect is helpful when unable to neutralize the strabismus 100%. • Can be used for diplopia as well as with visual field loss. DISADVANTAGES • Compromises acuity, especially with higher power prisms • Glare and chromatic aberration • Difficult to clean, fall off • Cosmesis. • Takes longer to cut the prism than it does to determine how much prism is required! DIPLOPIA – DOUBLE VISION • 4 basic categories of diplopia that we encounter in practice are acquired strabismus, decompensated phoria, mechanical diplopia and monocular diplopia. • Can use prism in the first 3. • Most of the diplopia that we encounter in the outpatient population falls into the first 2 categories. PRIMS USE IN ADULT DIPLOPIA • Gunton and Brown • Current Opinion in Ophthalmology 2012 • Review summarized the results of prismatic correction in adults based on the cause of diplopia • Main findings: - Satisfaction with prismatic correction is achieved in ~80% of all adult patients with diplopia - Careful selection of patients for prism correction, management of their expectations, and continued follow-up to monitor the symptoms are critical to success. NONSURGICAL TREATMENT OF DIPLOPIA • Bartiss, M. Current Opinion in Ophthalmology. 2018 • Recognizes the importance of utilizing non-surgical approaches to treating diplopia • Successfully treating diplopia decreases the risk of injuries and maximizes independence and quality of life and these concerns are especially important as patients age. CRANIAL NERVE PALSIES The cranial nerves most often affected are CNIII (oculomotor), CNIV (trochlear) and CNVI (abducens). CRANIAL NERVE PALSIES • Cranial nerve palsies are very common in patients with vascular disease, in particular diabetes (the trifecta – diabetes, hypertension, high cholesterol) and in brain injury. • Sudden onset diplopia. • Will often improve with time, usually within 3-6 months. • In the past, would just patch but that is particularly not appropriate for a patient in a rehab setting where the goal is to get back to walking and performing activities of daily living. MANAGING CRANIAL NERVE PALSIES • We can use a Fresnel prism to eliminate the diplopia by determining the amount of prism that is necessary to achieve single vision. • A Fresnel prism is placed on the lens in front of the deviating eye. MANAGING CRANIAL NERVE PALSIES • If both a horizontal and vertical deviation (CN3 and 4), can use 2 prisms – highest power on the back of the lens, lower power in front or an oblique prism. • Monitor monthly and can change the power as needed. • The prism blurs the vision slightly, which is helpful if we cannot eliminate the diplopia completely. • If the palsy remains after 6 months, can consider surgery or have the prism ground in the glasses at that time. DETERMINING THE AMOUNT OF PRISM • Measure the amount of deviation in the phoropter by having the patient look at a single letter and use rotary prisms until the image is single. • Verify outside the phoropter using a prism bar – often will require less prism in free space. • Use loose prism to ensure the patient sees single at all distances with the prism. • Demonstrate a fresnel prism. • May need to place the prism on the non-dominant eye if the blur is an issue. STEPS TO DETERMINING PRISM NEEDED Phoropter Prism Bar STEPS TO DETERMINING PRISM NEEDED Loose Prism Fresnel ASSOCIATED PHORIA • Fixation disparity is a small ocular misalignment of one eye or both eyes when the two eyes are fixating on an object during normal binocular vision. • The amount of prism which is required to reduce the fixation disparity to zero has been called “the associated phoria”. • Since you are measuring the misalignment binocularly, can prescribe the amount of prism exactly. NEAR PHORIA TESTS CASE #1 Cranial Nerve Palsy CASE #1 • 58 yo male hemorrhagic CVA 2 months prior, inpatient at Polytrauma Rehabilitation Center, aphasia, still in post traumatic amnesia. Seen bedside. • Currently using +1.50 OTC reading glasses • Distance vision fine, horizontal diplopia since CVA, dizziness. • Unaided DVA OD: 20/30 OS: 20/40-1 PHNI OU: 20/30-2 • Unaided NVA OD: 20/160 OS: 20/100 OU: 20/80 CASE #1 • Cover Test: Distance and near: Right hypertropia, XP • Fixation: slow with multiple fixations • EOMs: jerky, end gaze nystagmus (-)diplopia • Nystagmus in downgaze • Damp Autorefraction: • OD: +0.25+0.75X158 • OS: +0.25+0.75X 115 • Cover Test with prism Bar: 14^BU OS • Subjective with loose prism: 16^ BU OS CASE #1 • Plan: - Rx given for SVD to purchase glasses in the community - Will apply 15^BU OS when he gets his glasses • 1-week later Bedside -Applied 15^ Fresnel BU OS -VA OU: 20/20-1 (-)diplopia -NVA cc: OD: 20/32 OS: 20/32 OU: double -Prism bar with reading glasses: single with 14^ BU OS -Plan: Applied 15^ BU POP OS to reading glasses CASE #1 • 3 days later – examination in exam room • DVA cc: OD: 20/20-1 OD OS: 20/20-2 OU: diplopia w/o prism • NVA cc: OD: 20/40 OS: 20/25 OU: 20/25 (-)diplopia w/o prism (struggles with crowding) • Maddox Rod at distance w/o prism: Vertical: right hyper Horizontal: eso • Maddox Rod at distance w prism: Vertical: tr right hypo Horizontal: ortho CASE #1 • Maddox Rod at near w/o prism: Vertical: right hyper Horizontal: exo • Maddox Rod at near w prism: Vertical: right hypo Horizontal: exo • Single line text acuity with prism: 20/25, miscalls a few words initially closing OS but could read the same OU • Von Graeffe Phoria: Distance Vertical: 11BD OD sees single Distance Horizontal: 2BO OS sees single CASE #1 • Distance prism assessment: Loose Prism: 12^BD OD Fresnel: 13^BU OS • Near Prism assessment: with +2.50 OTC readers Prism bar in downgaze: 8^BD OD Loose prism: sees single with 8^BD OD Fresnel: prefers 9^BU OS for reading • Plan: Applied 10^ BU Fresnel to back side of OS and 3^ BU to front in SVD Applied 9^ BU Fresnel to back side of OS in SVN CASE #1 • 2 weeks later: 3^ Fresnel fell off the front of the lens, says the images are “slightly off”. Dizziness has improved • Distance acuities remain the same, slightly double at distance with 10^ Fresnel • Single line text acuity with prism: reads 1M (8pt) but miscalls words, tended to spell words out first. Does best with 12pt 2/2 crowding • Repeated the prism eval process and final determination was to go back to the 15^ BU OS and keep the near he same. CASE #1 • Saw him every 2 weeks • No change in distance or near visual acuity • Repeated the process - Cover test and maddox rod distance and near with and without prism - Von Graeffe, prism bar, loose prism, fresnel - Reading acuity - Changed power of Fresnel based upon the above testing results • Switched prism to OD when beginning to show signs of suppression CASE #1 • After 6 weeks of no change in the magnitude of the deviation, rx given for Bifocals with 10^ split vertical prism and 8^ SVN with split vertical prism. • He is walking more now so advised to remove the bifocals while walking. • Followed him monthly and when the magnitude remained stable for 6 months, surgical consult was placed. • Continue with SVN prism glasses for extended reading, SVD with prism for walking and bifocals when seated CASE #1 • Prism Evaluation Distance: • Post strabismus follow-up: Prism Bar: 4^BD OD • Manifest Refraction: Loose Prism: 3^BD OD OD: +0.75+0.25X172 20/20-1 “Better” without any prism OS: +0.25+0.50X097 20/20 • Prism Evaluation Near: OU: 20/20-2 Sli vert overlap Prism Bar: 1-4^ BD OD “no difference, Add: +2.50 OD: 20/26 OS: 20/20 6^BI OD “better” OU: 20/16 Loose Prism: “No difference” with 2^BD OD and with 6^ BI OD CASE #1 • No distance glasses needed since he is happy with unaided visual acuity • Rx for SVN given without any prism • Recommended reading stand for reading since has diplopia and nystagmus in downgaze. • Would like to try vision therapy for high XO at near • Scheduled with BROS for vision therapy CASE #1 • Started telerehab with BROS – vision therapy to improve convergence at near as well as binocularity • He works so more convenient • He used the computerized Home Therapy System and the brock string • Goal is to be able to drive CASE #2 • 73 yo male referred to our clinic because of a complete right homonymous hemianopsia 2/2 CVA • Health/ocular history positive for Diabetes (A1C 8.1), hypertension, high cholesterol, recent CVA and prior Bell’s Palsy • Good visual acuity at distance and near • All other findings were normal • No neglect • Applied 15^ Base right sector prism to the back of the right lens in his glasses and referred him to BROS for training CASE #2 • Returned 3 months later.