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Questions and Answers
What is a common symptom associated with convergence insufficiency?
Which factor is least likely to contribute to convergence dysfunction?
Which of the following management strategies is recommended for convergence dysfunction?
What does NOT indicate the presence of convergence dysfunction?
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Which visual hygiene advice is appropriate when addressing convergence insufficiency?
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What is the purpose of using flipper lenses during the accommodation facility test?
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During dynamic retinoscopy, what is being actively encouraged?
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What does a neutralization during dynamic M.E.M. retinoscopy indicate?
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What is a common result when there is accommodation lag observed?
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Which age group is likely to have the fastest facility rate during accommodation tests?
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What is the primary goal when measuring the amplitude of accommodation?
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What method should be followed if the difference in measurement is greater than 2 cm when assessing amplitude?
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What is the expected action for early presbyopes if their amplitude is less than 2.00DS?
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During the assessment of accommodative facility, what is the procedure when adding plus lenses?
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Which factor is not influenced by small pupil size in relation to accommodation testing?
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What must be ensured about the target during the NPC test?
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What is the primary purpose of using base IN prisms during testing?
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What does a significant difference between break and recovery points exceed?
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What is expected of the normal near point of convergence (NPC) range?
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What symptoms may indicate convergence dysfunction?
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What happens when convergence breaks during the NPC test?
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Which method can increase sensitivity in identifying subjective break points?
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What is convergence paralysis?
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In patients with convergence fatigue, what common symptom is typically reported?
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What does convergence spasm refer to?
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What does an accommodative lag greater than +0.75 suggest?
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What is the suggested management for accommodative insufficiency?
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What characterizes accommodative infacility?
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Which condition is indicated if a patient has low LAG or LEAD of less than +0.25?
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What is characterized by habitual over-accommodation?
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When would a patient typically require a 'boost' for their lag?
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Dynamic retinoscopy results show equal values in both eyes. What does this imply?
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What is the significance of a dynamic retinoscopy result of +0.50 to +0.75?
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Study Notes
Convergence Testing
- Near Point of Convergence (NPC) is a test that assesses the ability of the eyes to converge (turn inwards) when looking at a near target.
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NPC Method is a method used to examine the near point of convergence, the test can be performed on hypermetropes, presbyopes and myopes.
- Hypermetropes should be tested whilst wearing spectacles.
- Presbyopes should be tested whilst wearing spectacles, in some cases, post Rx, multi-focal or bifocal lenses could be used (to be determined by the professional).
- Myopes and Low Hypermetropes should be tested without spectacles unless otherwise instructed by the professional.
- Base-IN Prism can be used to assist with convergence in Myopes, as lens edge can impact convergence.
Instructions for NPC Testing
- Ensure the patient understands the instructions.
- Lights should be ON so the target is visible.
- Encourage the patient to maintain "natural position".
- Perform the test at slow and steady speed.
- A small amount of blurring is normal as the test is focused on convergence and not accommodation.
Monitoring the Patient
- Pay close attention to the patient, monitor their responses and eye movements.
- When convergence breaks, there are typically two responses:
- Pathological Diplopia: The patient recognizes double vision (positive response).
- Suppression: The patient experiences suppression, meaning the target still appears single (no diplopia response).
Subjective & Objective NPC
- Subjective Assessment involves listening to the patient’s report of double vision.
- Objective Assessment involves observing eye movements when convergence breaks.
- It’s important to consider if the subjective and objective NPC points match and whether the patient reported diplopia or suppression.
- It's crucial to note which eye diverges first.
Recording NPC Data
- After identifying the break point, withdraw the target and note where the patient reports single clear vision (BSV) is achieved (Subjective Recovery Point).
- Also, observe when single clear vision is achieved objectively (Objective Recovery Point).
- Measure the midpoint between the convergence break and recovery point.
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If convergence is good and consistent:
- Record the average of 3 repeated measurements.
- Note which eye breaks objectively (if observed).
- Record whether the patient reported a subjective comment.
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If the difference between break and recovery exceeds 5cm:
- Record both the break and recovery points.
- Consider the possibility of convergence fatigue if the difference is significant.
- Repeat the test to check for fatigue effects, if convergence worsens by more than 1cm with each attempt, note the deterioration.
Normal NPC Range
- Normal NPC: typically ranges from 6cm to 10cm, with some professionals extending the range up to 12cm.
- Suspect NPC ranges from 12cm to 15cm.
- Interventions might be considered if NPC exceeds 15cm.
Factors Affecting NPC
- NPC tends to decrease with age.
- Presbyopes may report blur before diplopia, in these cases, continue to probe for double vision.
- Consider developmental factors, such as the patient’s height and arm length.
Jump (Step) Convergence Test
- The test involves shifting focus from a distant target (typically 50cm) to a near target (15cm) and vice versa.
- It assesses the smoothness of vergence eye movements
- This test is considered abnormal if no vergence movement, jerky vergence movement, or version movements are observed.
Convergence Disorders
- Convergence Insufficiency: Difficulty maintaining convergence for comfortable single binocular vision (BSV) at near, causing blur at near.
- Convergence Fatigue: Tiring of convergence when performing sustained or repeated near tasks.
- Convergence Inertia: Difficulty sustaining convergence at near, making it hard to maintain single vision for prolonged periods.
- Convergence Spasm: Inability to diverge the eyes or relax convergence.
- Convergence Paralysis: Complete inability to converge the eyes.
Convergence Insufficiency
- Can be caused by various factors including anatomical (large pupillary distance, divergent position of eyes at rest), weak general health, thyroid eye disease, psychological stress, and age.
- Urban lifestyle and excessive close work can contribute to convergence insufficiency.
- Overuse of accommodative convergence can lead to a decrease in convergence.
- This includes myopes reading without spectacles, new presbyopes with near specs, and recently corrected low hyperopes.
Convergence Dysfunction
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All types of convergence dysfunction can be highly symptomatic:
- Blurred vision at near.
- Jumbling of words at near.
- Intermittent horizontal diplopia at near.
- Relief when one eye is closed.
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Muscular fatigue is another common symptom, leading to discomfort like:
- Aesthenopia (eye strain).
- Periorbital tension, worse with close work.
- Ease when eyes are closed or with rest.
- Difficulty changing focus from distance to near.
- Eye irritation, itching, burning, and gritty sensation.
- Possible nasal conjunctival hyperaemia (potentially a sign of convergence insufficiency).
Management of Convergence Dysfunction
- Visual hygiene advice should always be provided.
- Remove the cause of the dysfunction if possible, particularly when symptoms are present.
- Vision therapy is often effective in improving convergence, usually through exercises.
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Refractive Modification:
- Consider spectacles for near vision for pre-presbyopic myopes, to stimulate accommodative convergence.
- Some base-in prism from concave lenses can be helpful.
- Prisms (Base IN) can provide short-term relief.
- Be aware that lack of symptoms could indicate suppression, therefore always check objective NPC.
Convergence Exercises
- Pencil to nose exercise: Start with the target at a distance and slowly bring it closer until diplopia or divergence is reported. Repeat and continue until the patient can sustain a normal near point (aim for 10cm).
- Near-far exercises (jump or step): Focus clearly on a near target then shift focus to a distant target. Keep alternating distance to near, keeping the target clear and single.
- Frequency: Perform exercises 10 minutes twice daily (for 10cm near point).
Amplitude of Accommodation (AoA)
- AoA: Measures the ability to focus on objects at different distances. Measured in dioptres (DS) where one diopter is equivalent to a one-meter shift in near point.
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Technique:
- Ensure adequate lighting and hygiene practices.
- Start with monocular then binocular measurements.
- Fully corrected balanced distance Rx should be in the trial frame.
- Use a near target (N5 or smaller visible print) and progressively bring it closer until blur is reported. Then withdraw the target until clarity is reported, repeat.
- If difference between measurements is less than 2cm, record the average. If difference exceeds 2cm, record the range.
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AoA Limitations:
- Presbyopes: If AoA is less than 2.00DS (50cm), ensure full distance prescription is worn.
- Depth of field: Can affect the reliability of the measurement.
- Early Presbyopes: Consider adding additional positive power to enable the initial view of the target at 50cm, then find the near point, and subtract the additional power from the final result.
Range of Accommodation
- This measurement assesses the ability to focus through positive and negative lenses.
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Technique:
- Fixate on a target at a consistent distance (monocular and binocular, better monocularly).
- Add increasing positive lenses until blur is observed.
- Add increasing negative lenses until blur is observed.
Accommodative Facility
- Measures the ability to rapidly adjust focus from near to distance, and back again.
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Technique: Utilize flipper lenses to alternate between +ve and -ve lenses (e.g., +/-1.00DS, +/-1.50DS, +/-2.00DS), viewing a near target at approximately 40cm.
- Replace positive lenses with negative lenses when vision clears.
- Repeat the process, counting the cycles per minute (one cycle is +ve, -ve, +ve).
- Normal facility can vary with age.
Objective Assessment of Accommodation
- Static Retinoscopy: Traditional retinoscopy with fixation at distance to induce zero accommodation (fogging), enabling assessment of dis-accommodation and accommodation fluctuations.
- Dynamic Retinoscopy: Performed while actively accommodating at near, assesses accommodative lag/lead by comparing dynamic refraction results with the stimulus accommodation.
Dynamic M.E.M. Retinoscopy
- Monocular Estimated Method: This subjective method assesses accommodation when viewing a near target (usually 40cm) while retinoscopy is performed at the same distance.
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Technique:
- Place lens before one eye, over the patient’s prescription.
- The fellow eye continues to fixate on the target.
- Quickly retinoscope to see if neutralization occurs (1 second/lens). The retinoscopy beam will dazzle the non-fixing eye.
- Remove the lens and adjust lens power (increasing or decreasing) to achieve neutralization. If the retinoscopy beam moves WITH the movement, add positive power (lag). If it moves AGAINST the movement, add negative power (lead).
Lag/Lead Interpretation
- Normal range for lag in pre-presbyopes is between +0.50D and +0.75D.
- Lag exceeding +0.75D indicates possible accommodative insufficiency or infacility, or under-corrected hyperopia.
- Lead or lags less than +0.25D could suggest accommodative spasm or under-corrected myopia.
- Large disparity in results between both eyes can suggest an unbalanced distance Rx or unilateral pathology.
Dynamic Retinoscopy: Sources of Error
- Similar to static retinoscopy: Small pupils, poor media, and scissors reflex can influence the results.
- Patient cooperation with fixation: Particularly important as they are looking directly at the light source.
- Working distance errors: Exaggerated if not performed at 40cm.
- Adaptation to lenses: Accommodation can relax further with positive lenses if they are not changed quickly enough.
### Accommodative Disorders
- Accommodative Insufficiency: Difficulty accommodating at near, having a remote near point considering age.
- Accommodative Lag: Underactive accommodation at near, leading to a lack of clarity when focusing on near targets.
- Accommodative Infacility (Inertia): Difficulty adjusting from near to distance vision.
- Accommodative Excess (Spasm): Over-activity of the accommodative system, causing blurry distance vision but clear near vision.
- Accommodative Paralysis: Inability to accommodate, typically diagnosed in people who are not yet presbyopic.
Accommodative Insufficiency & Lag
- These conditions affect the ability to accurately adjust accommodation to near vision.
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Management Strategies:
- Refraction: Prescribe maximum plus and minimum minus for optimal distance vision.
- Near Point Exercises: To improve accommodative function, near point “accommodation” exercises can be recommended.
- Consider an add for near vision: To help "boost" accommodative lag, improving near visual comfort and using objective methods (such as dynamic MEM retinoscopy) to determine the correct add power.
- Fixation Disparity (if present): If a patient has a decompensated syndrome of ocular dominance, consider neutralizing the eso "slip" with binocular positive lenses.
Accommodative Infacility
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Management Strategies:
- Refractive Management: Ensure optimal correction (maximum +ve, minimum –ve).
- Consider an add for near work: To improve comfort and ease the strain of near tasks.
- Exercises: Recommended to improve accommodative facility, these can include simple exercises like push-up and jump accommodation or more challenging exercises like using flipper lenses. Perform exercises 2-6 times daily and review progress every 4-6 weeks.
- Manipulation of Refractive Correction: If the patient is unwilling or unable to do exercises, consider adjusting their refractive correction to facilitate better accommodative function.
Accommodative Excess (Spasm)
- Characteristics: Habitual over-accommodation, leading to a perception of blur when viewing distant objects, whilst near vision is clear.
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Management:
- Refraction: Determine the maximum plus power, as the patient may want more minus than necessary.
Hofstetter's Formula:
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A formula used in optometry to estimate amplitude of accommodation based on the proximity of an object and the total refractive error of the eye.
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It incorporates a patient's age and is used to determine if the patient's accommodation is within the normal range.
Key Points
- Comprehensive eye examinations are essential to identify and manage convergence and accommodative disorders.
- Visual hygiene advice is crucial, particularly addressing factors like excessive close work, screen time, and proper lighting.
- Vision Therapy is often effective in addressing these disorders, especially involving exercises to improve accommodative and vergence function.
- Refractive management plays a vital role in managing refractive errors to optimize visual performance and reduce visual fatigue.
- Monitoring and follow-up are important for understanding the effectiveness of treatment and making adjustments as needed.
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