Binocular Vision Lecture 3 - Eye Deviations PDF

Binocular Vision Lecture 3 – Classification of eye deviations Professor Phillip Buckhurst By then end of the session you will be able to: Define orthophoria, heterophoria and heterotropia Classify heterophoria and heterotopia  Motor and sensory fusion Binocular single vision is dependent...

Binocular Vision Lecture 3 – Classification of eye deviations Professor Phillip Buckhurst By then end of the session you will be able to: Define orthophoria, heterophoria and heterotropia Classify heterophoria and heterotopia  Motor and sensory fusion Binocular single vision is dependent on both motor fusion and sensory fusion: – Motor fusion This is the fusional vergence that is used to move the eyes from the dissociated position to the active position so that the image falls on corresponding retinal points – Sensory fusion Once the image is located at the retinal corresponding points higher level processing needs to occur in order to achieve a perceptual fusion of the two retinal images  Achieving dissociation There are many ways of dissociating the eyes (making the eye assume its passive position) – Covering an eye – Using a septum – Distorting the image When dissociated, the eyes assume their passive positions - determined by physiological and anatomical features: tonic vergence -- postural and fixation reflexes if the other eye fixates a distant object proximal and accommodative convergence  Orthophoria Example of Orthophoria (No deviation) This is present when the active and passive positions are the same nose Fusional vergence is NOT required for bifoveal fixation When one eye is covered it Dissociated Position does not move out of position Oculomotor balance (OMB) is perfect nose This is not very common Associated Position  Heterophoria Example of heterophoria This is where the dissociating (exophoria) and active positions collide A latent deviation becomes manifest when the eyes are dissociated Is present if the eye under the nose cover moves Fusional vergence is required for bifoveal fixation Dissociated Position – Motor fusion reflex eliminates the deviation when the obstacle to sensory fusion (cover) is removed nose Does not affect binocular vision Considered physiological Active Position  Heterotropia Example of heterotropia (right exotropia) Where fusion is not possible The reflex has either failed to develop or is unable to function The visual axis are misaligned It is manifest even when no nose attempt to dissociate the eyes has been made Binocular vision is impaired – Considered pathological When fixating on a distance target Classification of heterophoria Direction Magnitude Fixation distance Compensation  Classification of Example of esophoria heterophoria – Direction nose ESOPHORIA (SOP, Eso) visual axes converge when Dissociated Position eyes dissociated Eye moves in when covered nose Active Position  Classification of Example of exophoria heterophoria – Direction EXOPHORIA (XOP, Exo) nose Visual axes divergent when eyes dissociated Eye moves out when covered Dissociated Position nose Active Position  Classification of heterophoria -- Example of R/L hyperphoria Direction R/L hyperphoria, or R hyperphoria nose Visual axes vertically misaligned when eyes dissociated Dissociated Position visual axis of RE above that of LE nose Active Position  Classification of heterophoria -- Example of L/R hyperphoria Direction L/R hyperphoria, or L hyperphoria nose Visual axes vertically misaligned when eyes dissociated Dissociated Position visual axis of LE above that of RE nose Active Position  Classification of heterophoria -- Example of incyclophoria Direction Eyes rotate about visual axis when dissociated nose Incyclophoria (incyclo) Eyes rotate around the visual Dissociated Position axis upon dissociation The upper poles of the iris are seen rotating nasally nose Active Position  Classification of heterophoria -- Example of Excyclophoria Direction Eyes rotate about visual axis when dissociated nose Excyclophoria (Excyclo) Eyes rotate around the visual Dissociated Position axis upon dissociation The upper poles of the iris are seen rotating temporally nose Active Position Classification of heterophoria -- Magnitude Horizontal and vertical heterophorias – Prism dioptres (∆) Cyclophorias – Degrees (°) Classification of heterophoria -- Magnitude How this is measured – By taking an educated guess – Using a Synoptophore (more on this next year) – By preforming a prism bar cover test (More on this later) Classification of heterophoria Fixation distance Needs to be stated at what distance the heterophoria was assessed – Distance (D) or near (N) Typical range of values: D: 2∆ SOP to 4∆ XOP N: 3-6∆ XOP, PHYSIOLOGICAL EXOPHORIA Classification of heterophoria Fixation distance A further classification can be made if the magnitude of heterophoria varies depending on the assessment distance – Basic heterophoria: D phoria = N phoria – Convergence insufficiency: Px is more exophoric at near – Convergence excess: Px is more esophoric at near – Divergence insufficiency: px is more esophoric at distance – Divergence excess: Px is more exophoric at distance Classification of heterophoria – Compensation COMPENSATED – Adequate fusional reserves – No symptoms UNCOMPENSATED – Inadequate fusional reserves – Symptoms (asthenopia) Classification of heterotropia Comitancy Frequency Laterality Direction Magnitude Fixation distance Age of onset Influence of accommodation Classification of heterotropia – Comitancy Recall your last lecture COMITANT – Deviation constant in all directions of gaze INCOMITANT – Deviation varies with direction of gaze Classification of heterotropia – Frequency CONSTANT – Tropia always present INTERMITTENT – Tropia present some of the time – Motor fusion can control tropia at certain times so that it becomes latent (heterophoria) – Can become manifest at the end of a stressful day CYCLIC – Rare condition, 48 hour rhythm (24 hours normal binocular vision, 24 hours manifest tropia) – Tends to become constant with time Classification of heterotropia – Laterality UNILATERAL – Patient constantly fixates with same eye (R or L) – VA often reduced in deviating eye (amblyopia) ALTERNATING – Either eye can fixate – VA usually approximately equal in both eyes  Classification of Example of Esotropia heterotropia – (right esotropia) Direction Esotropia The deviating eye is convergent nose Left eye is fixating on a distance target Classification of Example of Exotropia heterotropia – (right exotropia) Direction Exotropia The deviating eye is divergent nose Left eye is fixating on a distance target  Classification of Example of hypertropia heterotropia – (right hypertropia) Direction Hypertropia The deviating eye is superior in position nose Left eye is fixating on a distance target Classification of Example of hypotropia heterotropia – (right hypotropia) Direction Hypotropia The deviating eye is inferior in nose position Left eye is fixating on a distance target Classification of Example of incyclotropia heterotropia – (right incyclotropia) Direction Incyclotropia The upper pole of the cornea nose has rotated nasally Left eye is fixating on a distance target Classification of Example of excyclotropia heterotropia – (right excyclotropia) Direction Excyclotropia The upper pole of the cornea nose has rotated temporally Left eye is fixating on a distance target Classification of heterotropia – Magnitude Units of measurement – Prism dioptres (∆) Horizontal and vertical phorias – Degrees (°) Cyclophorias Classification of heterotropia -- Magnitude How this is measured – By taking an educated guess – Using the Hirschberg’s method (more on this later) – Using a Synoptophore (more on this next year) – By preforming a prism bar cover test (More on this later) Classification of heterotropia Fixation distance Needs to be stated at what distance the heterotropia was assessed – Distance (D) or near (N) Can have a tropia at near but not at distance and vice versa Classification of heterotropia Fixation distance A further classification can be made if the magnitude of heterotropia varies depending on the assessment distance – Basic heterotropia: D tropia = N tropia – Convergence insufficiency: Px is more exotropia at near – Convergence excess: Px is more esotropic at near – Divergence insufficiency: px is more esotropic at distance – Divergence excess: Px is more exotropic at distance Classificaiton of heterotropia – Age of onset CONGENITAL – Developed in first few months of life or at birth ACQUIRED – Onset during childhood or later in life Classification of heterotropia – Influence of accommodation NON-ACCOMMODATIVE – Magnitude of tropia independent of amount of accommodation exerted ACCOMMODATIVE – Magnitude of tropia changes as accommodation exerted – May be fully or partly accommodative – Due to accommodative convergence relationship Note: Much more on this later Binocular Vision Lecture 3 – Classification of eye deviations Professor Phillip Buckhurst