OPT503 Lecture 8 Handout PDF

Binocular Vision Lecture 8 – Convergence and accommodation Part 2 Professor Phillip Buckhurst By the end of this session you will be able to: Discuss the management of convergence insufficiency and accommodation insufficiency Understand how to calculate the AC/A ratio Relate AC/A ratio val...

Binocular Vision Lecture 8 – Convergence and accommodation Part 2 Professor Phillip Buckhurst By the end of this session you will be able to: Discuss the management of convergence insufficiency and accommodation insufficiency Understand how to calculate the AC/A ratio Relate AC/A ratio values to binocular vision problems Convergence Insufficiency The inability to obtain or maintain sufficient convergence for binocular vision at near Convergence Insufficiency symptoms General difficulties with near vision Tired or sore eyes Intermittent diplopia Headaches Symptoms can get worse when px is tired or ill health Convergence insufficiency signs Subjects will have a reduced NPC Subjects also have a poor response with the jump convergence test The majority of patients with convergence insufficiency will also have a decompensating exophoria at near Accommodation can also be reduced Convergence insufficiency management Convergence insufficiency management Base-in prism reading glasses, Exercises or vision therapy Basic (target or pencil push ups) Stereograms (Vectograms) Lifesaver cards Computer Orthoptics Base-in prism reading glasses For children – Research shows that this is not an effective treatment for convergence insufficiency in young adults For adults – This may help in adults however is not conclusive – One trial showed that it reduced symptoms but did not improve the NPC Pen to nose exercises Start with the pen at around ½ meter and then bring it in close until the patient observes diplopia – Or if the practitioner observes the eyes diverging Then the Px should move the pen away from there eyes until single Then bring in close again and repeat This test requires the patient to recognize diplopia Should be conducted for 2 minutes at a time 5 times a day  Brock string exercises Px holds one end of the string to their nose The other end is held away and down slightly Px to converge onto each bead in turn Once Px has reached their near point of convergence (cant converge any further) then they diverge following each bead in turn Should be conducted for 2 minutes at a time 5 times a day Stereograms Stereograms Getting px to converge onto the pencil whilst relaxing accommodation onto the stereogram Means that px will increase convergence with near target Increasing fusional reserves (more on this later) Lifesaver cards These are the same as the stereograms except they are designed so that the pencil can be held at different distances Aperture rule Again similar to stereogram except for the aperture means that the person has to converge to see each eyes image Computerised orthoptics A computer based stereogram There are different makes Accommodation insufficiency The inability to obtain or maintain sufficient accommodative focus at near relative to the expected accommodation for the age Accommodation Insufficiency symptoms General difficulties with near vision Tired or sore eyes Blurred vision for near Headaches Symptoms can get worse when px is tired or ill health Accommodation insufficiency signs Subjects will have a reduced amplitude of accommodation (relative to expected value) Subjects also have reduced accommodative facility The majority of patients with accommodative insufficiency will also have convergence insufficiency Px have accommodative lag >1.00D with dynamic retinoscopy Accommodative insufficiency management Reading spectacles Exercises are the main treatment – Ramp accommodation exercises (no evidence to support) – Jump accommodation exercises (no evidence to support) – Lens Flipper (rock) exercises (very little evidence to support) Note: still more research needs to be done to decide what is the best form of treatment for AI Accommodative exercises do not work for presbyopes It is impossible to cure presbyopia with exercises There are many books which claim to be able to restore youthful vision in presbyopes – None of which are backed up by evidence Ramp accommodation Start with some wrting at around ½ meter and then bring it in close until the patient can no longer focus on the writing Then the Px should move the writing away from there eyes until back in focus Then bring in close again and repeat This test requires the patient to recognize blur Should be conducted for 2 minutes at a time 5 times a day Jump accommodation exercises Need two accommodative targets one at distance and the other at near Writing needs to be large enough for Px to see with both eyes Px asked to jump accommodate between the two tasks Should be conducted for 2 minutes at a time 5 times a day Lens Flipper (lens rock) excercises Px wearing full distance correction Px holds detailed accommodative target (small writing) 40 cm infront of them Px (or examiner) holds lens flippers infront of eyes – Use ±2.00D lenses if possible Px to swap from positive to negative and back again each time they are able to focus on the writing through the lenses Writing needs to be large enough for Px to see with both eyes Px asked to jump accommodate between the two tasks Px to do the test monocularly and binocularly Should be conducted for 2 minutes at a time 5 times a day AC/A Ratio AC/A Ratio The amount of accommodative convergence (AC) induced by 1 dioptre of accommodation (A) AC/A Ratio A Px with a normal AC/A ratio will converge by the correct amount when accommodating – Normal AC/A ratio is around 3 to 5 units of accommodative convergence for every 1 unit of accommodation A Px with a low AC/A ratio will not converge enough when accommodating A Px with a high AC/A ratio will over-converge when accommodating Note: what is deemed as normal varies between books Low AC/A Ratio Patient will not converge enough when accommodating Convergence insufficiency likely Near exophoria or exotropia likely (eyes staying out at near) High AC/A Ratio Patient will over converge when accommodating Convergence excess likely – This could be latent hyperope that you haven't refracted properly Less of an exo at near Near esophoria or esotropia likely (eyes converging too much at near) AC/A ratio and age The AC/A ratio remains relatively consistent until the onset of presbyopia Not clinically useful in presbyopic patients (as they have reduced or no accommodation) Measuring the AC/A ratio Two methods The calculation method The gradient method The Calculation method AC / A = PD + ( n ´ ( D'- D)) Where AC/A is in Dioptres PD = Pupil distance (cm) n = fixation distance when measuring near phoria (m) D’ = near phoria (Δ) For exophoria assign a D = distance phoria (Δ) negative value For esophoria assign a positive value The Calculation method For this method you need to measure: Pupillary distance (PD) – You measure this using your PD rule – This is the pupillary distance for a distant object Distance phoria (dissociated) – You can measure this in different ways Distance maddox rod Distance prism bar cover test Near phoria (dissociated) – You can also measure this in different ways Maddox wing Near prism bar cover test Near fixation distance when measuring phoria – Measured in meters Note: if using the Maddox Wing then the fixation distance is 0.3m Example You have a patient with a pupillary distance of 60 mm. You preform a prism bar cover test for distance and with the patient fixating at 40 cm. The patient has a 3 dioptre exophoria at distance and a 10 dioptre exophoria at near. What is their AC/A ratio AC / A = PD + ( n ´ ( D'- D)) AC / A = 6 + ( 0.4 ´ (-10 - (-3))) AC / A = 3.2D Therefore your patient has an AC/A ratio within the normal range Example 2 You have a patient with a pupillary distance of 55 mm. You preform a prism bar cover test for distance and with the patient fixating at 40 cm. The patient has a 1 dioptre exophoria at distance and a 13 dioptre exophoria at near. What is their AC/A ratio AC / A = PD + ( n ´ ( D'- D)) AC / A = 5.5+ ( 0.4 ´ (-13- (-1))) AC / A = 0.7D Therefore your patient has a low AC/A ratio The Gradient method You measure the size of a phoria You measure the size of the phoria again but with a spherical spectacle lens (of known power) infront of the eyes The change in formula caused by the lens gives a measure of the AC/A ratio of the Gradient AC/A The basic gradient method The phoria is measured Phoria is measured again with a minus 1.00D lens infront of the eyes The difference in phoria provides the AC/A ratio Example – If the phoria is 10Δ exo then is measured again with a -1 and it is now 4Δ exo – Therefore the AC/A ratio is 6/1 The modified gradient method Maddox wing is used to measure the baseline near phoria A -2.00DS lens is added infornt of each eye and the near phoria is measured again The AC/A ratio is calculated using the formula: AC/A = (phoria with minus lens – baseline phoria) Power of minus lens Use a positive value for esophoria Use a negative value for exophoria AC/A Ratio Clinically both methods are used – Calculation Only requires a cover test and simple math – Gradient Quick and easy Differences between the two methods – Proximal vergence – Lag of accommodation Difference between the two methods: – Calculated AC/A includes the effect of proximal vergence – Gradient AC/A measures the near phoria twice at a fixed distance, proximal vergence is held constant and thus does not alter the final result Recording findings Record method: calculated / modified gradient test Only of value in pre-presbyopes E.g. AC/A (calculated) 4ΔD Binocular Vision Lecture 8 – Convergence and accommodation Part 2 Dr Phillip Buckhurst