OPT503 Lecture 7 Handout PDF

Binocular Vision Lecture 7 – Convergence and accommodation Prof Phillip Buckhurst  By the end of this session you will be able to: Measure the near point of convergence and jump convergence in your patients Measure accommodation using a variety of methods  The near vision tr...

Binocular Vision Lecture 7 – Convergence and accommodation Prof Phillip Buckhurst  By the end of this session you will be able to: Measure the near point of convergence and jump convergence in your patients Measure accommodation using a variety of methods  The near vision triad The near triad refers to the synkinetic actions of: Accommodation Accommodation Convergence And pupil response. These occur together with near vision Convergence Pupil Miosis We will return to this (More of this later) when we look at the pupils Convergence Problems with convergence can result in many problems particularly with near vision There are two main aspects of convergence movements to consider 1. Pursuit convergence Moving an object slowly towards the eyes 2. Jump convergence A change of fixation to an object at a different distance The near point of convergence (NPC) The near point of convergence (NPC) This is a measure of pursuit convergence This is defined as the closest point (maximum convergence) for which the binocular single vision is still maintained Measurement taken from the nose in cm The near point of convergence (NPC) – how to measure Should be preformed routinely Room lights on Near correction used (if presbyopic) Most common targets to use are the line target on the RAF or a pen tip It is important to hold the target slightly below primary position to simulate the more natural near vision position Get the patient to tell you when the line goes double Explain that it does not matter if the line goes blurry The near point of convergence (NPC) – how to measure Move the target towards the patients nose This is an objective test as well as a subjective one and so watch the patients eyes Record the distance in centimeters when your patient reports diplopia or when one eye diverges – It is common for a Px to not recognize diplopia, in these patients the only way of determining NPC is by recognizing when one eye is no longer looking at the target Encourage the Px to try to keep the target single for as long as possible If the px can converge to nose then record as » NPC: to nose The near point of convergence (NPC) – how to Record If the px can converge to nose then record as » NPC: to nose Otherwise record the NPC in centimeters (The RAF rule has a centimeter scale on the side to help) The near point of convergence (NPC) – Results A normal NPC would be less than 7.5 cm (Again RAF rule shows the normal ranges) For NPC greater than 7.5 then the px may have convergence insufficiency Jump Convergence test Jump Convergence test This is a measure of jump convergence This is defined as the ability to alternate between two targets requiring different convergence demands Measurement is subjective and requires an assessment of the speed and quality of movement The Jump convergence test – how to measure Room lights on Near correction used (if presbyopic) Use a letter on the distance test chart as the distance target – Should be one line above the visual acuity of the worst eye Use the tip of a pen, held at 15 cm from the patient in primary position, as the near target Get the patient to change their fixation between the two targets repeatedly Look at the movement of the eyes it would be prompt and smooth The Jump convergence test – how to record If the movements of both eyes are smooth and fast then record as » Jump good to 15 cm If the movements are slow or jerky the record as » Jump poor to 15 cm If there is no movement of one eye then the eyes have not converged record as: » No jump to 15 cm Note: In some cases you can get an over- convergence followed by a corrective movement. This is regarded as a normal response Accommodation Problems with accommodation can also cause problems with near vision There are several methods that can be used to assess accommodation Methods for assessing accommodation Used clinically Push up test for amplitude of accommodation Accommodative facility Dynamic retinoscopy Other methods (Used in research) Defocus curves (you did this in OPT107) Open field auto-refractor Open field abberrometery Note: You may get a chance to use the research methods in your final year project or if you do a PhD Push-up test for amplitude of accommodation Push-up test for amplitude of accommodation This is a subjective measurement of accommodation which is influenced greatly by depth of focus Defined as the closest point for which focus can be maintained Measurement taken from the nose in Dioptres Push-up test for amplitude of accommodation – how do measure Should be preformed routinely Room lights on Distance correction in place – This test should be preformed following subjective refraction and distance binocular vision check Needs a high detail accommodative target – Most common target is the writing on the RAF rule It is important to hold the target slightly below primary position to simulate the more natural near vision position Push-up test for amplitude of accommodation – how do measure Measure Right eye first by occluding the left eye Choose the smallest word the Px can read Move this target slowly towards the Px Get the Px to tell you when the word becomes blurry – Encourage them to try focus as much as possible When the Px can no longer make the word clear this is the blur point Note the value in dioptres – This can be found on the RAF ruler Move the target back until it becomes clear again this is the recovery point Note the value in dioptres The amplitude of accommodation is the average of the blur and recovery point Push-up test for amplitude of accommodation – how do measure Repeat the test for the left eye and binocularly Several reports advise that to improve accuracy you need to repeat this test 3 times per eye – Little evidence to support this Record in dioptres » RE: 9D, LE: 9D BE: 11D Binocular amplitude should be greater than monocular Push-up test for amplitude of accommodation – the results Compare your results with the expected accommodation range for the age of patient Remember that a patient with greater depth of focus will show a better AOA on this test – Depth of focus is increased with small pupils If AOA is lower than expected by 1.50 Dioptres or greater then accommodation insufficency is expected Push-up test for amplitude of accommodation – expected values Minimum (D) = 15 – (0.25 x age) Expected (D) = 18.5 – (0.3 x age) Age Minimum Average 10 12.50 15.50 20 10.00 12.50 30 7.50 9.50 40 5.00 6.50 45 3.75 5.00 50 2.50 3.50 55 1.25 2.00 60 0.00 0.50 Note: the table has been derived from the Hofstetter fomulae (above) Accommodative Facility Accommodative Facility Jump accommodation -- Assessment of the rate of change of accommodation Does not measure the amount of accommodation Can help diagnose problems Need to use ±2.00DS flippers Accommodative Facility – how to measure Room lights on Distance correction in place Place near chart at 40 cm and get Px to look at a word on the smallest line they can see Start with the +2.00DS lenses infront of the eye and then swap to the -2.00DS lenses Ask your Px to tell you when the words go clear again (they have focused through the negative defocus) Then clear swap back to the +2.00DS lenses When the words go clear again then swap back to the negative lenses The purpose of the test is to time how many complete cycles the patient can achieve – One cycle is the change from one stimulus and then back again Accommodative Facility – how to measure Do test both monocularly and binocularly Record number of cycles the patient can compete in one minute – Cycles Per Minute (cpm) » RE: 10cpm, LE: 11cpm, BE: 7cpm Much debate over the number of cycles that constitute normal Average values are around 11cpm monocular and 8 cpm binocular Accommodative Facility – alternative methods Swapping between different optical defocuses is known as lens rock Swapping between different physical distances is known as distance rock Dynamic Retinoscopy Static Retinoscopy Static retinoscopy refers to the technique you know at the moment and is what we use to assess a distance prescription Your px looks at a distance target You neutralize the reflex and then account for your working distance Distance target Examiner Patient Retinoscope Dynamic retinoscopy Dynamic retinoscopy is used to assess near vision You use a near target You can either neutralize the reflex by using lenses (modified estimate method) or by changing the distance of the target (Nott technique) Examiner Patient Near target Retinoscope Dynamic Retinoscopy -- Monocular Estimate Technique (MET) In this technique the target for your patient should be an accommodative stimulus (letters) The working distance for this technique is 40 cm The target should be placed at the same distance as your retinoscope The lights should be dim enough so you can see the reflex but bright enough that your patient can see the target The patients distance Rx should already be in place You do NOT fog the other eye Examiner Patient Near target Retinoscope Dynamic retinoscopy MET -- how to preform If the patient accommodates precisely to the near target (which is in the same position as the retinoscope) then you should see a neutral reflex – Accommodative response = Accommodative stimulus If the patient accommodates less than they should (accommodative lag) then you will see a “with movement” (more plus required) – Accommodative response < Accommodative stimulus If the patient accommodates more than they should (accommodative lead) then you will see an “against movement” (more negative required) – Accommodative response > Accommodative stimulus Typically a patient will accommodate less than needed (accommodative lag) Examiner Patient Near target Retinoscope Dynamic retinoscopy MET -- how to preform If the patient accommodates precisely to the near target (which is in the same position as the retinoscope) then you should see a neutral reflex – Accommodative response = Accommodative stimulus If the patient accommodates less than they should (accommodative lag) then you will see a “with movement” (more plus required) – Accommodative response < Accommodative stimulus If the patient accommodates more than they should (accommodative lead) then you will see an “against movement” (more negative required) – Accommodative response > Accommodative stimulus Typically a patient will accommodate less than needed (accommodative lag) Examiner Patient Near target Retinoscope Dynamic retinoscopy MET -- how to preform You need to measure the amount of accommodative lag (or lead) Do this by estimating the size of the reflex (for experienced examiners only) Or by placing a lens of the power of the estimated lag (or lead) infront of the eye and quickly checking the response – You can only hold the lens in place for a half second as it will disrupt the accommodative response and will give a false reading Examine the reflex along the horizontal meridian only and record the power required to achieve neutral Examiner Patient Near target Retinoscope Dynamic retinoscopy MET -- Interpreting results Record the dioptric value: » (MEM) RE: +0.25DS LE: +0.75DS If accommodative Lag is greater than +1.00 DS then accommodative insufficiency can be expected If accommodative lead is found than it suggests accommodative spasm Examiner Patient Near target Retinoscope Dynamic retinoscopy the Nott method Instead of using lenses to neutralise the movement you can keep the target at the same distance and just move the retinoscope either towards or away from the patient Another alternative is to move the target and keep the retinoscope at the same distance – However this alters the accommodative demand and so influences the results Dynamic retinoscopy the Nott method – How to preform The set up is the same Start with both your retinoscope and target at 40 cm and see what the reflex is like If the reflex is neutral then the patients accommodative response is equal to the accommodative demand – Note down your findings Examiner Patient Near target Retinoscope Dynamic retinoscopy the Nott method -- how to preform If accommodative lag is found then you need to: Keep the target at 40 cm Move your retinoscope backwards until you get a neutral reflex Examiner Patient Near target Retinoscope Dynamic retinoscopy the Nott method – the results The dioptric distance of the target is the magnitude of accommodative stimulus – E.g. if the target is at 40 cm then the accommodative stimulus is 2.50D The dioptric distance of the retinoscope when the reflex is neutral is the magnitude of accommodative response – E.g. if your retinoscope needs to be 2/3 m away from your px to achieve a neutral reflex then the accommodative response is 1.50D Examiner Patient Near target Retinoscope  Dynamic retinoscopy the Nott method – the results Accommodative lag = accommodative stimulus – accommodative response e.g. Accommodative lag = 2.50D – 1.50 = 1.00D If accommodative Lag is greater than +1.00 DS then accommodative insufficiency can be expected If accommodative lead is found than it suggests accommodative spasm Examiner Patient Near target Retinoscope  Dynamic retinoscopy the Nott method – Example 2 Your near target is located 40 cm infront of your patient You need to hold your retinoscope 1 meter away from your patient to achieve a neutral reflex What is the accommodative lag and is it within the normal range Accommodative stimulus = 40cm = 2.50D Accommodative response = 1m = 1.00D Accommodative lag = accommodative stimulus – accommodative response Accommodative lag = 2.50D – 1.00D = 1.50 D Examiner Patient Near target Retinoscope Homework Practical Binocular Vision Assessment by Eperjesi and Rundstrom -- Chapter 5 Ophthalmic clinical Procedures by Eperjesi, Bartlett and Dunne – Chapter 9 Binocular Vision Lecture 7 – Convergence and accommodation Prof Phillip Buckhurst