2/21/2010 Prescribing the Spectacle Correction Donald J. Getz Classical Approach: written in every text, is to prescribe maximum plus and to fully correct any measurable anisometropia: Ok if ortho D I F F E R E N CE S B E TW E E N TH E D I F F E R E N CE S B E TW E E N TH E Object quite strongly, since it rarely has proven successful Object quite strongly since it rarely has proven successful CLAS S I CAL AN D B E H AVI OR AL Maximum plus stabilizes the angle and thus they are more M E TH OD S I N TH E TH E R AP Y likely to develop ARC F OR S TR AB I S M U S AN D Unless plus produces alignment AM B LYOP I A ( W H Y OU R W AY I S B E TTE R !) Prescribing the Spectacle Correction Using the peripheral part of the cornea When measuring the refractive error of an Since that part of the cornea is flatter and more amblyopia, must be kept in mind that this toroidal, will find more plus and more cylinder, thus measurement is likely not being made along the giving the illusion of an anisometropia. optic axis of that eye. If you correct it, it will always remain an advantage Since the majority of amblyopes have an eccentric Si th j it f bl h t i for the patient to use this false line of sight since it f th ti t t thi f l li f i ht i it fixation and they are not fixating with their fovea, the will provide him with the best acuity. line of sight will pass through a peripheral portion of In addition, the aniseikonia created by the difference the cornea. in lens powers will make binocularity more difficult to create. Prescribing Prescribing Amblyopia: Exotropia: Reduce the power found in the fixating eye from 0.50 to 1.00 Never use more minus that the amount of minus that restores diopters standard visual acuity. Make both lenses relatively equal in power Even though this will likely reduce the angle of deviation it is done at the expense of increased accommodative effort, which creates Forget cylinder Forget cylinder stress, which in turn, is likely to reduce academic performance. Esotropia: Don’t let the patient use accommodation to correct an exo Usually prescribe additional plus if it significantly reduces the deviation angle of deviation: Esotropia: The first stage of VT incorporates a large amount of If the ACA relationship is tight and cannot be loosened up, accommodative work to allow us to prescribe more plus then there is not choice and bifocals must be prescribed. The segs should be set very high 1
2/21/2010 Prescribing Patching Divergence Excess Three schools of thought Usually they are 35 exo at distance and close to ortho at near Direct patching of the good eye Usually have high ACA: 10 or 12 to 1. Inverse occlusion: They used to be high eso at near and in order to survive Eccentric fixation through the reading task, they solved the problem by using lots Amblyopia Amblyopia of negative relative convergence and thus they became ortho at f ti l ti d th th b th t Binasals near and high exo at distance Surgical intervention is usually a failure because if they get aligned at distance then they have esophoria at near Primarily this is an accommodative-convergence problem Prescribe a bifocal to eliminate the effect of the ACA and then VT is successful. No Patching VT Not needed to get results – if used they generally aggravate the child and/ or parent and makes them dislike the VT and me. Patching hardly ever works VT For Strabismus VT For Strabismus It’s like throwing a baby into a swimming pool A few kids will learn how to swim But most kids will end up hating the water Monocular General Principles for Successful Strabismus Therapy Monocular Skills Same visual direction Early in career – not much attention here Distance Over the course of my career – more and more importance Size Both visual fields need to be lined up in the same Speed p common visual direction – some differences that are co o sua d ect o so e d e e ces t at a e negative: Spatial location Z-axis location Timing differences between channels If too different, then one is suppressed. Monocular VT is a must to make both circuits equal 2
2/21/2010 Equal Behavior Versions Information Processing Saccades Space Matching Accommodation McDonald Form Field Pleoptics Pleoptics Use an afterimage to tag the fovea Macula Integrity Tester Involve the person in small exacting tasks which Photoflood Lamp require the use of the fovea After Image Techniques: Death Ray After Image Transfer Body Bilaterality Do Not Ignore Traditional VT with Strabismics If versions and saccadics are accurate with one eye Developmentally and not with the other there is no way to get the two Team two sides of the body first channels to work together. Learn control of gross muscles first Strabismus is from head to toe Accommodation is usually good with one eye and Walking rail W lki il miserable with the other i bl ith th th With Eccentric Fixation, the only accommodation present is If we ignore this aspect, we do so at our own peril the consensual response and we are not acting in the patients’ best interest In fovea there is a 1-to-1 hookup between cone, bipolar, ganglions and optic nerve cells/ fibers Therefore: once central fixation is achieved lots of accommodative work must be done 3
2/21/2010 Body Bilaterality Eliminate Suppression Developmental Sequence Usually does not take a great deal of time and effort Team Body First Using intermittent light has made this easier Lights flash at approximately the alpha rhythm (10 cps) Learn Gross Muscles First Instruments such as the TBI Strabs – work from head to toe Much harder to suppress flashing lights at this speed – the light is Much harder to suppress flashing lights at this speed the light is on and off again before the suppressing circuits can go active Strobe lights are very useful Walk around with one in my hand Whenever suppression occurs, simply shine on the target being suppressed or directly into the eye that is being suppressed. Monocular Work in a Binocular Field Simultaneous Vision Single slide of Vectograms Binasal occluder with ruler Anaglyph Vectograms Rotoscope Polariod and Mirror 4-Ball Cards 4 BAR Reading Projector 4 Ball Cards Simultaneous Vision Posturing City and plane Pierce Light R-G Lite Brite Vertical Prism Vectograms Red Green “V” Lights R-G Filter with overhead Lines and light g Septum Feel what eyes are doing 4
2/21/2010 Physiological Diplopia General VT Principles Once suppression has been weakened or eliminated, ABE we need to bridge the gap between monocularity and Alphabet Pencils binocularity. Brock String Monocular work in a binocular field Feedback Simultaneous vision Simultaneous vision with the person having to move their eyes some to achieve alignment. Align Red/ Green target Feel what they are doing Physiological diplopia (Brock String) – best means of feedback, which is a major principle of VT; allows patient to monitor his own performance. Fusion Reflex Fusion Reflex When an image moves off the fovea there is an Obtain Fusion or Lustre increase in the tonus of the extra-ocular muscles to 1 or 2 Diopter prism bring the image back to the fovea Regain Fusion Involuntary fusion movements to maintain single, binocular vision Exists only in the foveal area due to 1-to-1 hookup During ductions they make involuntary movements to compensate, which only become voluntary after diplopia begins and they make a voluntary movement to overcome it. Test by fusion or lustre at any distance with a small prism (1 or 2 diopters) and see if they make small movement to reestablish fusion. Lustre VT From this Base No figure – just ground The rest of the time is spent with traditional binocular VT and is about 50% of the total case. Red Green Lenses In the past we tended to come in to the binocular Blur helps phase too fast. Avoid split field p 5
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