Tests for Accommodation: Push-Up, Pull-Away, Minus Lens & More | For Optometrists & Ophthalmologists

Understanding Accommodation in the Eye

Introduction to Accommodation

• Dr. Amrit introduces the topic of accommodation, focusing on variable tests related to it.

• Accommodation is defined as the process by which the eye adjusts its optical power for clear focus on nearby objects, primarily through contraction of the ciliary muscle.

Key Terms: Near Point and Far Point

• Important terms include:

• Far Point (Punctum Rotum): The farthest distance at which small objects can be seen clearly; varies with static refraction.

• Near Point (Punctum Proximum): The closest distance for clear vision; recedes with age.

Refractive Status of the Eye

• In a normal (emmetropic) eye, the far point is at infinity and near point typically around 33 cm or 40 cm.

• For hypermetropic eyes (farsightedness), the far point is virtual and lies behind the retina, while myopic eyes have a real far point in front of the retina.

Variable Tests for Accommodation

• Six key measurements are used to assess accommodation:

• Range of accommodation

• Amplitude of accommodation

• Accommodative response

• Accommodative facility

• Positive relative accommodation

• Negative relative accommodation

• Lead and lag of accommodation

Calculating Range and Amplitude of Accommodation

• The range of accommodation is calculated as the difference between near point and far point distances.

• Amplitude of accommodation measures dioptric power differences needed for focusing at near versus far points.

Example Calculation

• Given a near point at 25 cm (0.25 m) and a far point at 50 cm (0.5 m):

• Range = Far Point - Near Point = 50 textcm - 25 textcm = 25 textcm.

Dioptric Power Conversion

• Converting distances into diopters:

• Near Point Power = 1/0.25 = 4 diopters.

• Far Point Power = 1/0.5 = 2 diopters.

• Amplitude = 4 textD - 2 textD = 2 textD.

Normal Values for Amplitude Based on Age

• The Hof formula estimates maximum amplitude based on age:

• Maximum: 25 – (0.4 times textage)

• Minimum: 15 – (0.25 times textage)

Understanding Amplitude of Accommodation in Patients

Calculating Amplitude of Accommodation

• The maximum acceptable amplitude of accommodation for a patient is nine diopters, with a minimum of five diopters and an average of 6.5 diopters for someone aged 40 years.

• If a patient's calculated amplitude is around three diopters, it indicates accommodative insufficiency, as it falls below the minimum acceptable level for their age.

Methods for Measuring Amplitude

• There are four methods to calculate the amplitude of accommodation: three subjective tests (push-up method, pull-away method, minus lens method) and one objective test (dynamic retinoscopy).

• Subjective tests rely on patient responses while the objective test relies on clinician observation. All tests are typically conducted at a comfortable near distance (33 cm or 40 cm).

Harmon's Distance and Pediatric Considerations

• Harmon's distance is used to determine appropriate near points for children, calculated from the elbow to the middle knuckle rather than using a standard distance like 40 cm applicable to adults.

RAF Rule Overview

• The RAF rule (Royal Air Force rule) consists of a graduated scale marked in centimeters or diopters mounted on a steel rod, used to measure both near point convergence and accommodation.

• It features a sliding target that can display various charts and text sizes necessary for testing accommodation; these include reduced Snellen charts and telephone directory sections.

Testing Procedures with RAF Rule

• The first three target drums on the RAF rule are specifically designed to assess near point accommodation by ensuring patients can read clearly at specified distances. The dot on a line measures near point convergence but will not be discussed further here.

• Each surface of the metal rod has different scales: one side shows centimeter increments, another displays equivalent dioptric power, while others indicate expected age scales and convergence status (normal/abnormal).

Monocular vs Binocular Measurement

Understanding Monocular and Binocular Testing

Differences Between Monocular and Binocular Testing

• Monocular testing measures the pure accommodative ability of the eye, preventing convergence effects.

• In binocular testing, convergence influences accommodation, leading to higher amplitude measurements due to combined effects.

• Amplitudes in binocular tests are typically 0.20 to 0.60 diopters higher than monocular measurements because they include contributions from convergence.

Overview of Accommodation Tests

• The first test discussed is the push-up test using a target from the RAF rule; moving it towards the patient is called a push-up test, while moving it away is termed a pull-away test.

• Dynamic retinoscopy involves keeping the target stationary while adding lenses to observe accommodative response during near fixation.

Push-Up Test Procedure

• Ensure patients wear their refractive correction for accurate measurement; this allows for calculating near point accommodation based on corrected far point at infinity.

• The procedure requires proper lighting and patient comfort as the target is moved closer at approximately 5 cm/second until sustained blur occurs.

Measuring Near Point of Accommodation

• The first sustained blur indicates when accommodation can no longer clear the target; measure distance from spectacle plane to this point for near point accommodation.

• Normal values for near point accommodation vary by age: about 7 cm at age 10, 25 cm at age 40, and around 33 cm at age 45.

Calculating Amplitude of Accommodation

• Use the formula textAmplitude = 1/textNear Point - 1/textFar Point ; since Far Point is infinity with corrections, only use Near Point for calculations.

• For example, if Near Point is measured at 10 cm (0.1 m), then amplitude equals 10 text diopters.

Pull-Away Method Explained

Pull-Away Test Procedure

• Similar setup as push-up but starts with a blurred target close to spectacle plane; move it away until clarity returns.

Understanding the Minus Lens Method in Accommodation Testing

Overview of the Minus Lens Method

• The minus lens method is introduced as a technique for testing accommodation, alongside the pull away method. It can be performed with or without the RAF rule.

• Concave lenses (minus lenses) stimulate accommodation, while convex lenses (plus lenses) relax it. This distinction is crucial for understanding their effects on visual acuity.

Testing Procedure

• Begin by determining the best visual acuity at near distances, using a target positioned 40 cm from the patient's spectacle plane.

• Start adding minus lenses in increments of 0.25 diopters and ask if the target remains clear. Continue until the patient reports sustained blur.

Calculating Amplitude of Accommodation

• To calculate amplitude, use a working distance of 40 cm, which requires approximately 2.5 diopters of accommodation (1 divided by 0.4 meters).

• If a patient tolerates -5 diopters at this distance, their total amplitude of accommodation would be 7.5 diopters (2.5 + 5).

Comparison with Push-Up Test

• The minus lens method typically yields values about two diopters less than those obtained from push-up tests due to differences in measurement techniques.

• In push-up tests, moving targets closer increases retinal image size and may lead to overestimation of accommodative ability.

Factors Influencing Measurement Accuracy

• The fixed position of targets in minus lens testing maintains constant retinal image size, providing a more accurate assessment of true accommodative ability.

• Depth of focus plays a role; patients might tolerate slight blurriness during push-up tests leading to inflated results compared to controlled measurements with minus lenses.

Dynamic Retinoscopy: Understanding Accommodative Amplitude

Introduction to Dynamic Retinoscopy

• The objective test discussed is Dynamic Retinoscopy, which provides an objective measure of accommodation, contrasting with subjective tests that rely on patient responses.

Difference Between Static and Dynamic Retinoscopy

• In Static Retinoscopy, the focus is on measuring the Far Point while keeping accommodation inactive by having the patient look at a distant object.

• Cycloplegic drugs are used in Static Retinoscopy to paralyze the ciliary muscle, ensuring static accommodation.

Principles of Dynamic Retinoscopy

• Dynamic Retinoscopy involves stimulating accommodation by having patients focus on near objects, allowing for measurement of various components like amplitude and response.

• The retinoscope's position relative to the focal point determines the type of reflex observed: neutral, against movement, or with movement.

Calculating Accommodative Amplitude

• To calculate accommodative amplitude using Dynamic Retinoscopy, place a fixation target at approximately 40 cm from the patient while ensuring they wear their distance correction.

• Conduct vertical streak retinoscopy in a dimly lit room; observe reflex changes as you move the retinoscope closer until neutral motion is no longer seen.

Observing Reflex Changes

• Continue moving the retinoscope closer until you observe a change from neutral motion to with motion; this indicates that the near point of accommodation has been reached.

• Measure the distance from spectacle lens to retinoscope at this last point of neutrality to determine near point accommodation objectively.

Conclusion on Objective Testing

Understanding Accommodation and Dynamic Roscopics

Key Concepts of Accommodation

• The amplitude of accommodation can be calculated using the formula: 100 divided by the distance in centimeters (cm). For instance, if reflex changes occur at 10 cm, the accommodative amplitude is approximately 10 diopters.

• Accommodation is a dynamic process that varies constantly. This variability is crucial for understanding how vision adjusts as objects move closer or further away.

Dynamics of Accommodation

• At different distances, accommodation levels change; it increases as an object approaches and reaches a maximum before diminishing when the object gets too close.

• The term "Dynamic Roscopics" refers to this continuous change in accommodation, highlighting its importance in assessing visual function.