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What is the definition of accommodation?
What is the definition of accommodation?
Accommodation is the mechanism by which the eye changes refractive power by altering the shape of the lens in order to focus objects at variable distances.
Which of the following is NOT a component of accommodation?
Which of the following is NOT a component of accommodation?
The far point for an emmetropic eye is at __________.
The far point for an emmetropic eye is at __________.
infinity
What is the near point at 10 years of age?
What is the near point at 10 years of age?
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What is the formula for calculating range of accommodation?
What is the formula for calculating range of accommodation?
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Calculate the amplitude of accommodation for an eye with a near point at 10 cm and a far point at infinity.
Calculate the amplitude of accommodation for an eye with a near point at 10 cm and a far point at infinity.
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What is depth of field?
What is depth of field?
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Which test is used to assess the near point of accommodation?
Which test is used to assess the near point of accommodation?
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Physical accommodation is the contractile power of the ciliary muscle.
Physical accommodation is the contractile power of the ciliary muscle.
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What is the relationship represented by AC/A?
What is the relationship represented by AC/A?
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Study Notes
Accommodation in the Eye
- Accommodation refers to the eye's ability to change its refractive power by altering the lens shape to focus on objects at varying distances.
- Increased curvature of the anterior lens surface is responsible for accommodation.
- Typically, both eyes accommodate simultaneously.
Mechanism of Accommodation
- Blurred retinal image prompts the process.
- Parasympathetic nervous system triggers ciliary muscle contraction.
- Relaxation of zonule fibers occurs, allowing the lens capsule to curve more.
- Results in increased lens thickness, decreased equatorial diameter, pupil constriction, and convergence.
Components of Accommodation
- Physical Accommodation: Actual deformation of the lens, measured in diopters (D).
- Physiological Accommodation: Contractile power of the ciliary muscle needed to increase the lens's refractive power, measured in myodiopters (mD).
Key Terminologies
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Far Point: Distance where the eye can see an object clearly without accommodation.
- Emmetropic eye: At infinity.
- Myopic eye: Real and in front of the eye.
- Hypermetropic eye: Virtual and behind the eye.
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Near Point: Closest distance at which objects can be seen clearly; varies with age (e.g., 7 cm at 10 years, 25 cm at 40 years, 33 cm at 45 years).
Measuring Accommodation
- Range of Accommodation: Difference between the far and near point.
- Amplitude of Accommodation: Difference in dioptric power needed for focusing at near versus far points.
Examples of Calculation
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For an emmetropic eye with a near point of 10 cm:
- Range of Accommodation: Infinity - 10 cm.
- Amplitude of Accommodation: 10D.
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For an uncorrected myopic eye with a far point at 50 cm and a near point at 10 cm:
- Range: 50 cm - 10 cm = 40 cm.
- Amplitude: 10D - 50D = 8D.
Depth of Field and Focus
- Depth of Field: Range of object distances that appear in focus, affected by camera aperture, lens focal length, and subject distance.
- Depth of Focus: Range of image distances where an out-of-focus image remains acceptably sharp, influenced by age, aberrations, and light conditions.
Assessment of Accommodation
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Assessment Techniques:
- Pushup Test using the RAF rule to measure near point of accommodation (NPA) and amplitude.
- Dynamic retinoscopy techniques to assess accommodative response.
- Use of accommodative flippers for dynamic accommodation.
- Measure range using NRA-PRA (Negative Relative Accommodation - Positive Relative Accommodation).
- Evaluate the accommodative-convergence relationship (AC/A ratio).
Tools for Measurement
- RAF rule for NPA: A sliding target is moved towards the eye until sustained blur occurs.
- Snellen chart to ensure clear vision is maintained.
- Measurements should be taken for each eye separately and combined.
NPA Measurement Process
- Patient wears full correction during testing.
- The sliding target identifies the closest distance at which vision remains clear.
- NPA determined in diopters correlates with the patient's age-specific expected accommodation.
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Description
This quiz covers the concept of accommodation in the context of vision science, exploring its definition, mechanisms, components, and assessment. Understand how the eye adjusts its lens to focus on objects at different distances. Ideal for students and professionals in ophthalmology and optometry.
