OPTM3133 Midterm Notes.pdf

OPTM3133 Notes Wk 1: Ocular Motility Testing & Sensorimotor Evaluation Extraocular Motility Testing Extraocular Motility (EOM) - Six muscles controlling the extraocular movem...

OPTM3133 Notes Wk 1: Ocular Motility Testing & Sensorimotor Evaluation Extraocular Motility Testing Extraocular Motility (EOM) - Six muscles controlling the extraocular movements - 4 Recti - 2 Obliques - Control by cranial nerves - Oculomotor (CN III) – SR, IR, MR & IO - Trochlear (CN IV) – SO - Abducens (CN VI) – LR Types of eye movements Primary position of gaze: Straight-ahead position - Monocular : - Ductions : monocular eye movements - Binocular : - Versional eye movements: - conjugate eye movements - both eyes move together - Vergence eye movements: - disconjugate eye movements - both eyes move in opposite direction Ductions - Ductions – Monocular eye movements - tested monocularly by covering one eye Six (6) types of ductions: Horizontal direction (z axis) Vertical direction (x axis) Cyclic or rotatory axis (y axis) - Abduction- eye moves - Supraduction or elevation – - Incycloduction or intorsion: away from midline eye moves upwards rotation of upper cornea - Adduction- eye moves - Infraduction or depression towards the midline towards the midline – eye moves downwards - Excycloduction or extorsion: rotation of upper cornea away from midline  Versions - Versions – binocular eye movements - tested binocularly by covering one eye Six (6) types of versions: Horizontal direction (z axis) Vertical direction (x axis) Cycloversion - Dextroversion: gaze moves - Supraversion or upgaze: - Dextrocycloversion: both towards the right gaze moves towards up upper corneas rotates - RE abducts and LE - Both eye moves up towards right adducts - Infraversion or downgaze: - Levocycloversion: both - Levoversion: gaze moves gaze moves towards down upper corneas rotate towards the left - Both eyes move down towards left - RE adducts and LE abducts Vergence Vergence: eye movements in opposite direction Convergence Divergence both eye moves towards the midline both eye moves away from midline - When we look at objects from Far -> Near - When we look at objects from Near -> Far distance - For example: look at a distance objects such - For example: reading, near visual task as TV from looking at a mobile phone. Extraocular motility: Agonist and Synergist  Agonist Synergist The primary muscle moving the eye in a given Muscles in the same eye that helps the agonist to direction produce a given movement. - For example: - Elevation: the agonist for RSR, RIO is the synergist. - Depression: For RIR, RSO is the synergist. Extraocular motility: Yoke Muscles - Yoke muscles: - Pair of muscles located in each eye that helps to move in desired gaze position - Each extraocular muscle in one eye has a yoke muscle in the other eye. - Clinically important - For example: - Right end gaze: RLR & LMR - Left end gaze: LLR & RMR - Right up gaze: RSR & LIO - Right down gaze: RIR & LSO - Left up gaze: LSR & RIO - Left down gaze: LIR & RSO Two Laws of extra-ocular motility - Antagonist: Muscles in the same eye that acts in the direction opposite to the agonist. - For example: - Right end gaze: For RLR, RMR is the antagonist - Left end gaze: For LLR, LMR is the antagonist  Herings’ Law of Equal Innervation Sherrington's Law of reciprocal innervation Equal and simultaneous innervation flows to yoke During eye movements, increased flow of innervation muscles to move the eyes in a particular direction of to contracting agonist muscle and decreased flow of gaze. innervation to relaxing antagonist muscle. - Yoke muscles in both eyes, one in each eye - Right gaze (Dextroversion): RLR & LMR Muscles in the same eye - Right up gaze (Dextroelevation): RSR & LIO - Right down gaze (Dextrodepression): Right end gaze Left end gaze RIR & LSO - Left gaze (Levoversion): LLR & RMR - RE: Increased - LE: Increased - Left up gaze (Levoelevationversion): innervation to innervation to LLR LSR & RIO RLR & decreased & decreased flow - Left down gaze (Levodepression): LIR flow to RMR to LMR and RSO - LE: Increased - RE: Increased The law also applied to vergence eye movements: innervation to innervation to - Convergence: LMR and RMR LMR & decreased RMR & decreased - Divergence: LLR and LLR to LLR to RLR Motility Test - Broad H Test Purpose - Restriction of eye movements in different gaze positions - Detects non-comitant deviation (deviation is different at different gaze positions) - Pain/discomfort during eye movements Procedure - Pen/pen torch - Move in a H pattern - Hold target at comfortable working distance; not too far or too close - Instruct the subject to follow the target, not to move their head - Symmetrical, restriction, under/over action of movement, (possible pathology- CN palsies) - Repeat 1-2 times Record - SAFE (Smooth, Accurate, full and - Extensive(Equal)) - Full, free, painless - Compare palpebral aperture size / scleral - show - Ask for - Diplopia (subjective), at any gaze - Pain or discomfort (subjective), at any gaze - Under and over actions: Fixations, Saccades & Pursuits - Loses place when reading - Skips words when reading - Reads same line /letters twice or skips a line - Excessive head movement while reading - Poor ability to copy from whiteboard - Misaligns columns of numbers - Repeats letters within words - Sports - catching ball, tennis - Close working distance Fixation The ability to maintain a steady fixation on a fixation target - Procedure: - Observation of fixation for 10 sec - Target used: accommodative target- pen, picture - Look for stability or refixations Saccade - Redirect the eyes fixation from one target to another - It is conjugate eye movement. for example: reading - Testing Procedure: - Harmon distance or at 30-40 cm - Two targets at 10cm apart from midline - NSUCO grading  - Five round trips - Test performed in standing position to look for body movements - No instruction to move or not to move head to be given Recommended test: NSUCO Grading scale - Rate the performance in 4 categories 1) Ability 2) Accuracy 3) Head movements and 4) Body movements For eg: Saccades (NSUCO method) - 5/5/5 or 2/2/3 Pursuits - Test the ability of following eye movements; - Helps to track a moving object in the environment, eg: follow a tennis ball. Testing Procedure: - Working distance 30-40cm - One target – move in a circle of 20cm diameter - Two clockwise and two anticlockwise directions - Test performed in standing position to look for body movements - No instructions to move or not to move head Recommended test: NSUCO grading scale - Rate the performance in 4 categories 1) Ability 2) Accuracy 3) Head movements and/or 4) Body movements For eg: Pursuits (NSUCO method) - 5/5/5 or 2/2/3  Stereopsis & Worth four dot test Sensory evaluation - Stereopsis - Fusion Stereopsis: Appreciation of relative depth due to retinal disparity - 3rd grades of binocular vision Three main requirements for stereoscopic vision 1) Large binocular overlap of the visual field 2) Partial decussation of the afferent visual fibres 3) Coordinated conjugate eye movements Critical - Pilots - Policemen, Railways, Ships, Drivers - Sports - Binocular Microscopes - Surgeons - Dentist - Optometrist - Microbiologist - Virtual Reality Stereopsis: Theory  Crossed Disparity vs Uncrossed Disparity - Uncrossed Disparity: Objects which are behind the object of focus produce uncrossed disparity. - Crossed disparity: Objects which are in front of the object of focus produce cross disparity. Two types of stereoscopic stimuli Line/contour (Local) Random dot Stereograms (Global) - Have monocular edges or boundaries - Computer generated stereograms in which separated on a background to produce there is a lateral shift in the dots, lines, or disparity pattern - Minimum threshold (stereoacuity) or maximum - These have no monocular cues or boundaries appreciation (gross stereopsis). Titmus Fly Test: Fly: - “Behavioural” response;  - Have observer pinch wings from side - 3000 arc sec Animals : - 400-100 seconds of arc - Wirt circles - 800-40 arc sec - Can turn upside down - or turn goggles upside down to test uncrossed disparity on rings - Monocular clues on first few circles Random stereo test - Dots background - Tests to 20 sec of arc disparity - Top 4 have the same disparity (except for the check) - useless for a threshold measurement - No monocular cues- useful for strabismus patients Frisby Stereo test - Depth perception and stereoacuity in arc sec - Stereoacuity of 600 to 15 arc sec - Without stereo goggles, screening - Forced choice tests with 4 options to select- 25% correct responses About the test - Three test plates of 1.5, 3, 6 mm thickness, tested one at a time - Four squares that contain triangular-like shapes in a random pattern - A hidden circle which appears to pop up from any one of the squares - Disparity is created by the displacement of random shapes by the thickness - Groove at the corner of correct response for examiner to identify - No polaroid goggles are required - Repeat for 10 times at 9 increasing test distances - Longer the distance the disparity is perceived, better the stereoacuity - Lowest disparity which the patient can reliably discriminate - Screening test suitable for younger children (6 months to 4 years) - Perform at 40 cm for 85 sec of arc stereoacuity - Use white background, primary gaze - Patient selects the square with a circle in depth - Movement of the plate or patient’s head: monocular cues Disparity What affects stereopsis & measurement of stereoacuity? - Duration of presentation - Practice - Luminance - Contrast - Low - Unequal - Blur - Unequal Worth 4 Dot Test (W4DT) - Tests Sensory status – Simultaneous perception & Sensory Fusion - Four lights – 2 Greens, 1 Red and 1 – White - Far distance- projector chart and at Near distance - Use Red-green goggles - See different lights through Red filter & Green filter - Red filter sees the Red light - Green filter sees the Green lights - White light will be seen - FUSION - Clinically correlate with Cover Test (motor testing) - Clinical Pearls: DO NOT explain to the patient that you are going to do Worth-4 dot Test. Testing 1. Explain the purpose of the test – how well both eyes are coordinate. Procedure 2. Explain about the test –describe the number and colours of light seen 3. Habitual distance & near correction 4. Use red filter in front of right eye and green filter in front of left eye. 5. Switch on the far W4DT light after the filters are worn. 6. Ask for the response and record accurately. 7. Repeat the test for near and ask for the response. 8. Record the findings for far and near working distance. Clinical Pearls: DO NOT switch ON the Worth dot test lights before the patient wears the filters. Red filter before Right eye Possible results Recording of results Depth of - If suppression is noted with room lights on, check W4DT with room lights off. suppression - Depth of suppression is Deep or more intense if suppression is reported even in dim illumination - MUST do WD4T test for 1. Entrance test esp for Children 2. Strabismus 3. Amblyopia 4. Anisometropia -  Wk 2: Measurement of Ocular Deviations Cover Test Primary Position of Gaze - When the eye is looking straight ahead with the visual axis parallel to the sagittal plane of the head, the eye is in primary position. - Object is at infinity; visual axes are parallel. Orthophoria Ocular condition in which the two lines of sight meet at the object of regard, even when one eye is occluded. Types of Ocular Deviations: Phoria and Tropia 1. Heterophoria or Phoria - It is latent deviation (not visible when you look at both eyes directly). - Ocular condition in which lines of sight are aligned on the fixation point in binocular condition but NOT in monocular condition. - Can be observed ONLY when one eye is covered. - Very common, 1-3 prisms of exophoria - It may be far, near or both. - It may be in horizontal (most common), vertical or both deviations(rare). - Binocular 2. Heterotropia or Tropia - It is manifest deviation (can directly look at the deviation when looking at the patient’s eyes). - Observed obviously mostly. - Ocular condition in one of line of sight is misaligned on the fixation point in binocular condition. - It may be far, near and/or both. - It may be in horizontal, vertical or both deviations (common). - Unilateral or bilateral (alternating or intermittent) - In intermittent deviation- initially the eye looks orthophoric and after cover test, it shows tropia. Deviation Direction Terminology - Orthophoria or ortho – no ocular deviation - Eso– inward deviation towards the midline - Exo – outward deviation away from the midline  - Hyper – eye turned up; - Hypo – eye turned down; - Incyclo– eye rotates inwards towards midline - Excyclo– eye rotates outwards away from the midline For example: - Horizontal deviations; - Distance exophoria, - (X right exophoria - wrong documentation) - Right exophoria - Vertical deviations: - Right hypertropia - Left hypotropia, e.g., if the left eye moves down compared to the right eye Types of Tropia - Exotropia : one eye is positioned outwards - Esotropia: one eye is positioned inwards - Hypertropia: one eye is positioned up - Hypotropia: one eye is positioned down Cover-uncover Test: Tropia Cover one eye & Observe the deviation in the uncovered eye for Tropia 1. Cover left eye and observe Right eye(RE) 2. Outward movement in RE (because eye deviated inside before) – Esotropia in RE 3. Remove the cover from LE 4. Right eye goes inward again 5. Now, cover RE, observe movement in LE 6. No movement in LE, no tropia in LE 7. Diagnosis: Right constant esotropia If no tropia, perform Cover-Uncover and observe the just uncovered eye for Phoria 1. Cover LE (left eye) 2. Remove cover from LE 3. Observe the deviation in the just uncovered eye – Left eye (LE) 4. LE moves in (because it moved out under cover) – Exophoria 5. Remove the cover and eyes regain fusion 6. Next when you cover and uncover RE, RE will inwards indicating exophoria. Similarly, observe esophoric deviation in figure at the bottom.  Phoria and Tropia Testing - Objective - Cover Test - Hirschberg test using a pen torch - Subjective - Howell card - Maddox Rod - Modified Thorington - Maddox wing - Prism dissociation (von Graefe test) Cover Test - Objective measurement - Require patient cooperation to fixate - Fixation target – one line better than BCVA for distance - Keep patient’s attention to the target (20/30 target) – for active and stable accommodation - Single letter - Room lights on → better for seeing ocular deviations - Do not block patients view for distance viewing Target for cover test: RE: 6/60-; LE: 6/6, Refractive Amblyopia - Use spotlight as fixation target. - RE can fixate the spotlight much better. Cover Test - Near - For near cover test – fixation stick - Sit directly in front of the patient - Targets that seek attention Types of Cover Test - Unilateral cover test/ Cover-uncover test – tropia/phoria - Alternate cover test – total deviation (includes latent and manifest deviation) - Prism base cover test – magnitude of total deviation - Simultaneous cover test – magnitude of manifest deviation All of these four tests are used to understand the presence, direction and magnitude of any ocular deviations. Cover Uncover Test  - Introduce cover in front of one eye first - Observe the response of the other eye that has not been covered - Then remove the cover to allow viewing under the habitual condition - Repeat it 2-3 times - If eye movement seen in not covered eye - tropia - If eye movement seen in just uncovered eye- phoria - Only test to distinguish the phoria from tropia Alternating Cover Test - Cover one eye for 2-3 s - Observe the movement in the uncovered eye - Remove cover from one eye and immediately transfer to the fellow eye - Prevent the binocular viewing so that complete dissociate both eyes - Total = latent + manifest - Observe the type of deviation – exo /eso/vertical - Estimate the total angle of deviation using prisms Unilateral Cover Test: Confirms Tropia Record: a. Left esotropia - LST → this is how we record left esotropia b. Left exotropia - LXT c. Left hypertropia d. Left hypotropia When the fixating eye is covered, the deviating eye takes an outward deviation, then it is esotropia. Prism Bar Cover test  - Measure magnitude of deviation - Total deviation = latent + manifest - The apex of the prism toward the deviation to neutralise it → the base of the prism is opposite to the deviation. Example: - Exo- base In prisms - Eso- base out - Hyper- base down - Hypo- base up Prism Neutralisation Right exotropia → base in prism is used to neutralise. Prism → shifts image position, so the light from the object of regards falls onto the fovea. - Loose prisms/Prisms bars - Exodeviation: Base In (BI) - Esodeviation: Base out (BO) - Right Hypertropia: - Base down(BD) in right eye - Right Hypotropia: - Base up(BU) in right eye NOTE: For prisms notations, it is mandatory to record eye for vertical deviations. No need to mention eye for horizontal deviations. For example: - For right exotropia CT: RXT, PBCT : 45 BI - For right hypertropia CT: Right Hypertropia, PBCT: 40BD in RE - For left hypotropia: CT: Left Hypotropia, PBCT: 35BU in LE Simultaneous Prism Base CT - Measures manifest component only - Using Cover-uncover test - Directly neutralise the deviation using prisms in the deviating eye Procedure: - Place the prism in the deviating eye  - Do a cover-uncover test - If deviating eye shows movement, prism is increased until no movement is noticed in the deviated eye. (if there is opposite movement, for example eye moves inward, we have overcorrected the deviation → have to reduce prism). Hirschberg Test (H’berg test) Otherwise called corneal reflex test - Shining a light onto the child's eyes from a distance (30-40cm) and observing the reflection of the light on the cornea with respect to the pupil. - The location of the reflection from both eyes should appear symmetric and generally slightly nasal to the center of the pupil. - 1mm = 7 deg - For example: Esotropia: Cornel reflex shifts to temporal iris - Exotropia: Corneal reflex shifts to nasal B. Right corneal reflex is displaced towards the temporal pupil margin → eye has turned inwards, leading to displacement of corneal reflex. C. Corneal reflex displaced towards the nasal pupillary margin → eye has turned out. Cover Test Subjective Tests Subjective tests of phoria measurements 1. Howell card (prac and theory) 2. Maddox Rod (prac and theory)  3. Maddox wing (prac and theory) 4. Modified Thorington (theory) 5. Prism dissociation (theory) How does a person with phoria/tropia perceive? Howell card - Performed in free space - Phoropter is not used - Quick - No occlusion - Perform at distance (3 m) and near (33 cm) - Eyes dissociate with prism- 6 BD - Dark bars are designed to promote accurate accommodation Maddox Rod - Subjective method - Several parallel plano-convex cylinders - Handheld or in the phoropter - Prevents sensory fusion - Pt will see a red line from the light source  - The red line is perpendicular to the axis of the cylinders - Accommodation not necessarily accurate - Good method for vertical deviation measures – accommodation does not affect vertical deviations Procedure: - Perform with patient correction - Place the Maddox rod in front of the right eye - Pt look at the spotlight target at 6m or 40cm - Ask the patient if they can see the red streak of light - Ask the patient the position of red line to the spotlight - Add prisms in front of left eye to measure the phoria - Patient reports the location of line and spot - If the red line is on left of spotlight – crossed diplopia – exophoria – Add BI prisms to neutralise the separation - If the red line is on right of spotlight – Uncrossed diplopia – esophoria– Add BO prisms to neutralise the separation Procedure: vertical phoria - If the red line is on above the spotlight – left eye image is at the bottom → Left hyperphoria– Add BD prisms to neutralise the separation. - If the red line is below the spotlight – right eye image is at the bottom → Right hyperphoria – Add BD prisms in right eye to neutralise the separation. Muscle Imbalance Method (MIM)/Modified Thorington Method - Free space or phoropter - Perform with penlight and Maddox rod - Helps to diagnose horizontal/ vertical diplopia - Measure at 40 cm and 3 m - Calibrated and numbers printed on card - Target is accommodative; accurate phoria measure Modified Thorington Method-Muscle Imbalance Card Procedure: - Perform with the correction - Dim the room light - Place Maddox rod in front of right eye - Shine the light through the central aperture of the card - Pt look at the letter and keep them clear - Pt then look at the spotlight and report the position of the red line to the spotlight Maddox Wing - A septum is used to dissociate the eyes - Right eye sees arrow(s) - Left eye sees numbers - Only measure at near (30 cm) - Easy to use - Odd numbers are to the right - Even to the left to decide the direction Procedure: - The room lights on - Pt looks through the horizontal slits to view the chart - Ask the Pt whether the arrow is to the right or left of the zero - The number on the scale indicates the magnitude in prism - Even numbers: exophoria, odd numbers: esophoria - Can measure the vertical deviation Prism Dissociation (Von Graefe) - Use phoropter - Perform at distance and near - Retinal images separated by a prism using 6BU in front of LE and 10 BI in front of RE - Allow accurate accommodation to target - Highly dissociating procedure Procedure: Horizontal Phoria - Perform over the correction - Vertical array of letters - Pt keep the letter clear - Use Risley prisms, 6BU in front of LE and 10 BI in front of RE - Ask the Pt to close their eyes while you are  placing prisms - Ask pt to ensure diplopia is appreciated Procedure: Vertical phoria - Perform over the correction - Horizontal array of letters - Pt keep the letter clear - Use Risley prisms, 6BU in front of LE and 10 BI in front of RE - Ask the Pt to close their eyes while you are placing prisms - Ask pt to ensure diplopia is appreciated - Reduce 6BU prisms to neutralise the separation - Ask the pt the position of the top image to the right or left of the bottom image AC/A Ratio - Accommodation Convergence/ Accommodation (AC/A ratio) - Degree of convergence for every diopter of accommodation - Abnormal AC/A ratio: binocular vision problems - It remains constant throughout the life until presbyopia - AC/A measurements after age of 45 years are of little value Methods of measurement: 1. Heterophoria method (calculated method) 2. Gradient method Method: 1 Heterophoria method - AC/A = Distance IPD (cm) + 0.4(Near Phoria – Far Phoria), IPD – interpupillary distance, WD = 0.4 m (40cm) - Normal AC/A = 4 to 6:1 - Exo:-ve sign; Eso: +ve sign Method: 2 Gradient method - Difference between near ocular deviation with and without added lens divided by lens power used. - AC/A = diff b/w phoria with glasses and lens / power of lens used  Wk 3: Vergence Tests Eye Movements for Binocular Vision Version or conjugate movements ○ Both eyes move in same direction ○ For eg : left gaze, up gaze, down etc ○ For eg: Saccades and Pursuit eye movements Vergence or disconjugate movements ○ Both eyes move in opposite direction either inward or outward ○ Convergence eye movements Highly developed ○ Divergence Vergence Terminology Convergence → both eyes move inward Divergence → both eyes move outward Supra vergence → one eye move upward and other eye straight Infra vergence → one eye move downward and other eye straight Vergence: Four Types Tonic Vergence Tone of muscle; no adequate stimulus, eye is aligned due to its tonic vergence Cannot be measured directly Proximal Vergence Awareness of nearness/ perception of distance Cannot be measured directly Accommodative Vergence → Accommodative Convergence – Far -> Near accommodative convergence Disaccommodation- Near -> Far Measured using minus lenses, change of distance AC/A ratio Fusional Vergence → retinal disparity Retinal disparity → convergence/ divergence Convergence Far -> Near Divergence Near -> Far Measured using prisms Vergence Demand Formula: Vergence demand = PD (in cm) x 100 / d ○ d → working distance Considering the distance from Centre of rotation to Spectacle plane :  ○ centre of rotation to corneal plane = (1.3cm (13mm) ○ vertex distance- spectacle plane to corneal plane)= +1.4cm (14mm) ○ So add 2.7 cm (1.3+1.4) to working distance (WD) Vergence demand = IPD (in cm) x 100 / (d +2.7 in cm) ○ WD = 40 cm, PD = 60cm ○ Vergence demand = 6.0 x (100/ (42.7) = 6x 2.34 = 14.05 ∆ one eye, 28.10 ∆ both eyes Clinical Measures of Vergence 1. Near point of convergence 2. Fusional vergence amplitudes Horizontal Vertical 3. Vergence Facility Near Point of Convergence: NPC To measure the gross convergence (tonic, proximal, accommodative, and fusional vergence) Quick and easy method Target ○ Pen tip ○ Accommodative single isolated target (recommended) ○ Ruler or measuring tape Ask for double => single Break & recovery point NOTE: ○ Measured from Lateral canthus ○ If Spectacle – Distance out spectacle + 2.7cm (vertex distance and center of rotation) Procedure With correction Use single isolated target Slowly moving the target from 40cm towards the bridge of nose Eyes slightly downward gaze Ask if the patient sees any double images and report immediately – Break point Then, bring the target back until single vision is regained - recovery point Measured from lateral canthus, NOT from corneal plane Repeated 2 or 3 times to check consistency If it recedes, repeat until consistent values Subjective – break point reported by patient Objective – patient does not report diplopia, but examiner notices eye deviation → they have broken their fusion → response cannot be trusted Accommodative Norms: break cut off : 5 cm recovery 7 cm  Target Abnormal: >= 6cm break and/or >7cm recovery Possible responses: 1. Not reporting diplopia until close to nose ○ NPC – TTN (till the tip of nose) 2. Reports double directly & then recovery ○ NPC(Acc target) : 10/15cm NOTE: 10 = break value, 15 = recovery value 3. Reports double directly & then recovery; worsens on repeated testing ○ NPC (using accommodative target) = 15/20 cm; recedes on repeated testing => document the most receded point 4. Reports double when one eye deviates out: ○ NPC: 15/18cm, RE moves out at the break (reports diplopia) 5. Not reporting diplopia, one eye deviates out, objectively measure the break point ○ NPC (obj) – 15/25 cm, no c/o diplopia, LE diverges out, LE suppression ; ○ Recovery point is when both eyes regain fusion observed when deviated eye moves in to fixation back Another Method Sensitive → this test cannot be controlled by accommodation, so its completely fusion in nature Using Non-accommodative target Penlight with Red-Green filter Penlight with Red Lens Transilluminator (not common) Norms for NPC using RG filter: 7/10 cm Record For eg, NPC (using RG filter) = 15/20 cm; recedes on repeated testing. Fusional Vergence Amplitude To assess the fusional vergence reserves - tests the strength of how one can converge and diverge maintaining single & clear BV Measured to assess motor fusion at a particular distance (no change in accommodation): ○ Fusional divergence – negative fusional vergence (NFV) BI (Base in prisms) ○ Convergence – positive fusional vergence- BO (Base out prisms) Fixation ○ Far - 6m ○ Near - 40cm Fixation target: ○ Linear accommodative target Measured ○ Risley/rotary prisms- Smooth vergence ○ Prism bar- Step vergence ○ Single prisms – NOT used as prisms need to be increased How do you Habitual correction perform the test? Use prism bar or phoropter Start to increase BI prisms → diverges and relaxes the eyes Vertical fixation target held at 6m or 40cm Ask for blur/break/recovery (subjective response)  Subjective response and objective eye movements Then repeat the same with BO prisms Recording NFV (far) : 4/8/4 (Smooth vergence) Accommodation; Divergence –> Disaccommodation ○ (quantified by CA/C ratio, clinically not measured) Measure of fusional vergence free from accommodation – single but blurry Break: End of fusional vergence & accommodative vergence – double and clear Recovery: Strength at which one regains fusion after break – single and clear Fusional Vergence Record: ○ Distance / Near ○ Step/smooth ○ Distance ○ (Blur/Break/Recovery) PFV: x/20/18 NFV: x/14/12 EXAM: Need to know the mean values for blur, break and recovery for smooth and step vergence, especially smooth vergence.  Clinical Implication of FVR Further assessment in Phoria: Exophores/intermittent exotropia– reduced PFV, but NFV intact Esophores/intermittent esotropia– reduced NFV, but PFV intact Sheard’s criteria: FV (fusion vergence) reserve blur must be at least twice that of phoria. Works very well for exophoria For example: Near :10 XP, PFV blur = 20 pd; No symptoms For example: CT (near) : 6 XP; Near PFV blur = 6 pd=> Symptomatic Prisms required = 2/3 of phoria – 1/3 FVR blur ○ Prisms = 2/3*(6) – (1/3)*6 = 4-2 = 2 Base In ○ RE:1 BI and LE:1 BI, equally divided between both eyes Percival's criteria: To be non-symptomatic, mid–point of phoria position must be in the middle one third of FV with 2/3 PFV and 1/3 NFV. Work very well for esophoria Example: NFV = 3 BI, PFV = 15 BO ○ Prescribing prisms = 1/3 (total range) – NFV ○ Total range = 15 + 3 = 18 ○ Prism = 1/3*(18) - 3 = 6 - 3 = 3 base out ○ Prescribing 3 BO will decrease PFV to 12 pd and increase NFV to 6 pd Prism can be prescribed based on Fixation disparity NOTE: Sheard’s criterion was a good discriminator for exo deviation. Percival’s criterion was good for eso deviations. Vertical Fusional Vergence Use the horizontal line as target Use one eye– vertical fusional reserves are limited Right supra– prism over right eye, BD, pushes the image up and hence moves eyes up Right infra– BU Left supra– BD Left infra– BU Record break/ recovery No blur point for Vertical fusional vergence For example ○ Right supravergence: 2/0.5BD in RE ○ Left infravergence: 1/0.5 BU in LE If there is no vertical deviation: R supra = R infra L supra = L infra R supra = L Infra L supra = R infra Normal range is about 4/2 or 3/1 Vergence Facility Also called jump vergence Assess the dynamics of fusional vergence system Useful test in symptomatic patients with normal fusional vergence Perform at near 12 BO / 3 BI Prism Flipper*  16 BOI/4BI, 8BI/8BO Use a vertical line of letter of 20/30 Procedure Free space, binocular Introduce 12ΔBO before each eye Ask the patient to make the letter clear and single Flip the handle and introduce the 3 Δ BI Ask the patient to report the clear and single vision Clearing 12 BO and 3 BI makes 1 cycle Count the number of cycles in 60 second period Normal range is 15 ±3 cycles/ minute Mention difficulty with BI or BO prisms Record: ○ Vergence facility (using 12BO/3BI) : 12 cpm, diff with BI prisms Summary Near point of convergence ○ Accommodative target ○ Red-green Target Fusional vergence Reserves ○ Horizontal Positive and Negative fusional vergence amplitudes/reserves ○ Vertical vergence Supra and Infra vergence amplitudes Vergence Facility