2014 binocular vision & amblyopia

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Basic Course Lecture given in Philippine General Hospital, Sentro Oftalmologico Jose Rizal, Lecture modified July 2014

Transcript of 2014 binocular vision & amblyopia

  • I. Binocular Vision and Retinal Correspondence II. Amblyopia Alvina Pauline D. Santiago, MD Pediatric Ophthalmology & Adult Strabismus Basic Course Lectures in Ophthalmology Sentro Oftalmologico Jose Rizal Philippine General Hospital September 2014
  • Binocular Vision & Retinal Correspondence
  • Theories of Binocular Vision Correspondence & disparity sensory binocular cooperation based on correspondence & disparity single visual impression, no depth binocular rivalry: diplopia horizontal disparity: depth within Panums fusional space
  • Terms Horopter locus of all object pts imaged on corresponding retinal elements at a given fixation distance Panums fusional space or area of SBV region in front of and at the back of the horopter that still allows SBV allows depth perception
  • Horopter Elliptical line that stimulate corresponding points on the retina Panums fusional space Area in front and behind horopter where objects stimulate non correspondings points and yet are still fusible as one retinal image
  • Physiologic diplopia Uncrossed diplopia Crossed diplopia
  • Theories of Binocular Vision Neurophysiologic theory visual stimuli from retina to visual cortex modified and coded only 25% binocularly driven cells are stimulated equally; 75% graded influence from R & L eye Macaque monkey: Ar 18; Rhesus: Ar 17-18 Lost binocular neurons do not recover
  • Binocular Vision Reduced panorama of vision Upright position Frontal eye position Visuomotor tasks improved Depth perception Orientation of body to environment
  • Visual Pathway
  • Normal Visual Development
  • Development of Visual Acuity
  • Macula Development Fine visual discrimination characteristic of high VA require sharply focused small objects as appropriate stimuli
  • Amblyoscope or haploscope
  • Amblyoscope 2 mirrors at elbow that reflect images from picture slides arms may be moved to align targets on each fovea
  • Amblyoscope Subjective angle amount in degrees the examiner must move amblyoscope arms for patient to see 2 pictures as superimposed during binocular viewing conditions Objective angle
  • Amblyoscope Subjective angle Objective angle deviation measured by alternate prism cover test during monocular viewing conditions
  • Amblyoscope Angle of anomaly displacement of the true fovea from pseudofovea zero if NRC; subjective = objective angle (+) if alternate cover test (objective angle) is not equal to subjective angle
  • Worths level of fusion First degree (simultaneous perception) Dissimilar targets presented Perceived at the same time in the same visual direction Second degree Third degree
  • Worths level of fusion First degree (simultaneous perception) Second degree (flat fusion) similar targets with dissimilar components (monocular suppression checks) Third degree
  • Worths level of fusion First degree (simultaneous perception) Second degree (flat fusion) Third degree (stereopsis) Same targets as 2nd degree + disparity
  • First degree simultaneous perception 2nd degree flat fusion 3rd degree Stereopsis
  • Normal retinal correspondence RE: circle LE: black dot Orthotropic Black dot in circle
  • Normal retinal correspondence Organization of visual space is such that the visual direction of each fovea is the same Angle of anomaly = 0 Patients with NRC always use fovea as center of reference
  • NRC, with strabismus To see black dot in circle, need to move arms of amblyoscope total of 40 PD
  • Difficulties in Testing NRC and strabismus If with dense large regional suppression, no subjective angle, difficult to superimpose images If monofixator, use targets for peripheral retina
  • Harmonious ARC subjective angle = 0 measured under binocular conditions Pseudofovea compensates for angle of deviation No subjective misalignment
  • Unharmonious ARC pseudofovea does not compensate fully for angle of deviation Angle of anomaly = objective angle - subjective angle
  • Amblyoscope Measures fusional vergenge amplitudes Angle of deviation Area of suppression Retinal correspondence Torsion Instrument convergence
  • Terms Retinal correspondence single vision: hallmark ARC vs NRC Retinal disparity & rivalry: diplopia and visual confusion
  • Abnormalities of binocular vision Diplopia Visual confusion Suppression Horror fusionis Anomalous retinal correspondence
  • Diplopia vs Visual Confusion Diplopia Object of interest seen by fovea of one eye and peripheral retina of the other eye Visual confusion Fovea of both eyes (or corresponding retinal points) sees 2 objects of interest interpreted as coming from the same point in space
  • Diplopia vs Visual Confusion
  • Suppression Suppression: alteration of visual sensation that results in inhibition or prevention of one eyes image from reaching consciousness Physiologic suppression prevents physiologic diplopia from reaching consciousness
  • Central vs peripheral suppression Central: pathologic extension of retinal rivalry prevents foveal image of deviating eye from being perceived Peripheral: Prevents awareness of the image on peripheral retina (2nd image)
  • Suppression Scotoma Esotropia Exotropia
  • Monocular vs Alternating suppression Monocular: unidirectional Dominant eye always predominate over image from deviating eye Alternating: bidirectional Suppression switches between the two eyes
  • Facultative vs Obligatory Suppression Facultative Present only when eyes are deviated Obligatory Present at all times, whether eyes are deviated or aligned
  • Amblyopia
  • Definition: Amblyopia Etymology: dullness of vision Greek: amblyos = dull Stem: ops = vision Observer (MD) sees nothing, and the patient sees very little von Graefe
  • Definition Unilateral or bilateral decrease in VA caused by pattern vision deprivation or abnormal binocular interaction for which no cause can be detected by physical examination, and which in appropriate cases, reversible by therapeutic measures von Noorden
  • Prevalence Approximately 2-2.5% of general population has amblyopia Military Recruits 1-3.2% Preschool children 0.5-3.5% Ophthalmic patients 4-5.3%
  • Normal Visual Development
  • Basic Mechanisms Abnormal binocular interaction Foveal pattern vision deprivation Combination of both
  • Susceptible Period Most sensitive first 2-3 years Decreases until age 6- 7 years complete visual maturation retinocortical pathways and visual centers resistant to abnormal visual input
  • Classification Reversible (functional) Strabismic amblyopia Anisometropic / ametropic amblyopia Visual deprivation amblyopia Idiopathic amblyopia Toxic / Nutritional amblyopia Irreversible (organic) Amblyopia in nystagmus Other ocular pathologies
  • Strabismic Amblyopia Higher prevalence in ET than XT because of nasotemporal asymmetry of retinocortical projections ET: fovea of deviating eye competes with strong temporal field XT: fovea competes with weaker nasal field