Refraction Principles and Case History
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Questions and Answers

What is the recommended prism diopter base-in for a patient using spectacle magnifiers with a +8.00 addition?

  • 8 prism dioptres (correct)
  • 10 prism dioptres
  • 12 prism dioptres
  • 4 prism dioptres

    • Why might binocularity be difficult to achieve for individuals with a +12.00 addition?

  • The eye muscles cannot adjust to such a high addition.
  • Manufacturing limitations restrict the maximum add for binocularity. (correct)
  • High additions cause blurry vision and make fusion impossible.
  • The visual cortex cannot process information from two eyes with such a large difference in magnification.

    • What is the primary concern regarding the use of monocular occlusion for low vision patients?

  • It can be uncomfortable for the patient and lead to headaches.
  • It can cause the preferred eye to become overused and deteriorate.
  • It can lead to a deterioration of vision in the occluded eye due to underuse. (correct)
  • It can lead to a loss of depth perception.

    • What is a potential challenge when prescribing bifocals with a +4.00 addition for an elderly patient?

    <p>The patient may experience difficulty adapting to the large difference in magnification. (A)</p> Signup and view all the answers

    Which of the following is NOT a factor to consider when prescribing spectacles for low vision patients?

    <p>The patient's preference for a specific spectacle design. (D)</p> Signup and view all the answers

    Why might a +4.00 addition be inappropriate for bench work, even if it improves acuity?

    <p>It can make it difficult to see objects at a close distance. (C)</p> Signup and view all the answers

    What is the primary concern with prescribing a +4.00 addition for an elderly patient?

    <p>The patient may have trouble adjusting to the new focus point. (B)</p> Signup and view all the answers

    What is the purpose of using fogging lenses and duochrome in low vision practice?

    <p>To evaluate the patient's binocular vision. (D)</p> Signup and view all the answers

    What is the recommended working distance for a patient with a visual acuity of 0.8 LogMAR (6/36 Snellen)?

    <p>3-4 meters (A)</p> Signup and view all the answers

    Why is it important to ensure a comfortable fit for the trial frame when refracting a low vision patient?

    <p>All of the above. (D)</p> Signup and view all the answers

    What is the optimal working distance for patients with visual acuities better than 0.6 LogMAR (6/24 Snellen)?

    <p>6 meters (B)</p> Signup and view all the answers

    What is the recommended minimum improvement in LogMAR acuity for a new prescription to be justified?

    <p>Two lines (D)</p> Signup and view all the answers

    For patients with acuities of less than 1.0 LogMAR, what is the minimum spherical change considered likely to provide noticeable improvement in vision?

    <p>1.0 dioptre (D)</p> Signup and view all the answers

    What is the recommended minimum cylindrical change for a new prescription to be considered beneficial for patients with acuities less than 1.0 LogMAR?

    <p>2 dioptres (C)</p> Signup and view all the answers

    Why is a pinhole acuity check often challenging for patients with central scotomas?

    <p>Pinhole tests obscure the central visual field, making it difficult for patients with central scotomas to see. (C)</p> Signup and view all the answers

    What is the primary reason for recommending a +4.00 addition for near acuity testing in low vision patients?

    <p>It provides a unit magnification when viewing an object at the least distance of distinct vision (25 cm). (B)</p> Signup and view all the answers

    What is the recommended working distance for near acuity testing in low vision patients?

    <p>25 cm (A)</p> Signup and view all the answers

    Why might younger patients prefer to accommodate rather than use a near addition for reading?

    <p>They have better accommodation abilities than older patients. (D)</p> Signup and view all the answers

    What is the primary benefit of using a stenopicslit in low vision refraction?

    <p>It assists in detecting refractive errors in patients with irregular astigmatism. (B)</p> Signup and view all the answers

    Flashcards

    LogMAR acuity chart

    A chart used to measure visual acuity using a logarithmic scale.

    Distance refraction

    The process of determining the best optical correction for vision at a distance.

    Pinhole acuity check

    A method to test vision by using small holes to reduce the effects of refraction errors.

    Cylindrical change

    Adjustment in prescription related to astigmatism affecting curvature of light.

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    Minimum change for prescription

    An updated prescription should ideally show a two lines improvement on LogMAR.

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    Near acuity

    Visual clarity for close objects, usually tested with reading charts.

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    Working distance

    The distance at which a patient is most comfortable reading, often around 25 cm.

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    Auxiliary lighting

    Additional lighting used to help visually impaired patients see better while reading.

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    Radical Retinoscopy

    A technique performed in darkness to refine retinoscopy in patients with medial opacities.

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    Keratometry

    A method to measure the curvature of the cornea, often used to detect astigmatism.

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    Irregular Astigmatism

    A form of astigmatism with uneven curvature of the cornea, affecting vision quality.

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    Down's Syndrome and Keratoconus

    Individuals with Down's syndrome have a significant risk (20%) of developing keratoconus.

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    Trial Frame Fitting

    Adjusting a trial frame for comfort and correctness before performing subjective refraction.

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    Vertex Distance in Refraction

    The distance from the back of the lens to the eye, critical for accurate refraction.

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    LogMAR Visual Acuity

    A scale for measuring visual acuity where lower numbers indicate better vision.

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    Working Distance for Charts

    Optimal distances to present letter charts based on patient acuity levels during vision tests.

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    Binocularity

    The ability to use both eyes together for depth perception and comfortable vision.

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    Base-in Prism

    Prism added to lenses to help align vision and facilitate fusion at near for binocular users.

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    Spectacle Magnifiers

    Eyeglasses with lenses that enhance vision, often used by visually impaired individuals.

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    Additions in Prescription

    The extra optical power added to lenses for near vision correction, often noted in positive numbers.

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    Occlusion in Vision

    The practice of covering one eye to improve vision or reduce strain on the stronger eye.

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    Fogging Lenses

    Lenses used in tests to reduce contrast and determine visual responses in low vision practice.

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    Bifocal Lenses for Elderly

    Spectacles with two sections for different distance viewing; may be challenging for older patients.

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    Illuminating Work Surface

    The act of ensuring that a work area is well-lit to aid visibility, especially important for elderly users.

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    Study Notes

    Refraction Principles

    • Principles of refraction remain constant, regardless of visual impairment.
    • Comprehensive case history is crucial, including medical, ophthalmic, visual, social, educational, and employment factors.
    • Task analysis is essential, asking patients to describe their problems.
    • Objective and subjective elements of refraction must be considered.
    • 8-10% of new low vision patients only require an updated prescription.

    Case History

    • Comprehensive case history is fundamental to providing appropriate low vision aids and advice.
    • Patients must feel comfortable and at ease during the consultation.
    • The practitioner should demonstrate genuine interest and expertise in visual rehabilitation.
    • Psychological aspects of sight loss and practitioner-patient interaction must be considered (e.g., Dodds et al studies).

    Medical History Questions

    • Questions should focus on relevant disabilities likely to affect daily function (e.g., rheumatoid arthritis, Parkinson's, multiple sclerosis).
    • Medical conditions affecting motivation (e.g., diabetes, terminal illness) should be addressed.
    • Ophthalmic history focuses on ocular health aspects related to visual impairment (e.g., cataracts, macular degeneration).
    • Educational, employment, and social issues related to visual impairment need to be discussed.
    • Tasks and rehabilitation should be addressed.

    Visual Function Questions

    • Questions should directly relate to the assessment of vision.
    • Questions need to be specific to prescribing and rehabilitation advice.

    Current Optical Corrections

    • Existing eyeglasses should be evaluated and prescriptions documented.
    • Patients must express their opinions about the usefulness of existing glasses.
    • Idiosyncratic responses should be documented and addressed.

    Retinoscopy

    • Accurate retinoscopy is essential for efficiency.
    • Factors affecting accuracy include media clarity, eye movements, and patient cooperation.
    • Using a rechargeable, halogen bulb retinoscope is recommended.
    • Reducing or eliminating background illumination can be helpful in challenging cases.
    • "Radical retinoscopy" with reduced working distance can improve image clarity.

    Keratometry/Corneal Topography

    • This is rarely used in routine low vision assessment, but can help confirm astigmatism (especially irregular astigmatism).

    Subjective Refraction

    • Trial frames should be comfortable and fitted like final glasses.
    • Spherical lenses are placed in the back of the trial frame; cylindrical lenses are placed in the front.
    • Fully-apertured trial lenses should be used to assess eye movements and fixations.
    • Refraction over existing glasses can clarify if changes are significant (using a Halberg trial clip).

    Distance Vision

    • Chart selection depends on visual acuity.
    • Patients with acuity under 1.0 LogMAR (6/60 Snellen) need 1-3 meters charts and 0.6-1.0 LogMAR (6/24-6/60 Snellen) should use 3-4 meters charts. Six-meter charts are for acuities better than 0.6 LogMAR.

    Near Acuity

    • Near acuity tests should be recorded using existing glasses and a standard +4.00 near addition.
    • Practical consideration is given to working distance.
    • The working distance may be 25cm for certain individuals.
    • Consider factors like lighting and patient comfort.
    • Use of fogging lenses is not generally helpful in low vision.

    Binocularity

    • Binocular vision is not a typical aspect for most visually impaired patients, but can be considered.
    • If binocularity is present in both eyes, base-in prisms may be used.
    • Maximum achievable addition for binocularity is +12.00 diopters.
    • Occlusion tests are recommended for patients lacking binocular vision.
    • Consider using different lens options that include options such as Bifocals.

    Spectacles Prescribing

    • Visual impairment or medial opacities can lead to unstable refraction.
    • Patients with high refractive error may be offered contact lenses.
    • Contact lenses may increase field expansion, particularly in aphakia, but magnifi cation may be reduced.
    • Consider factors including cost, discomfort, and ability to function with the lenses.
    • Refractive surgery considerations need careful consideration and discussion with a surgical team.

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    Related Documents

    Refraction Principles for Visually Impaired Patients PDF

    Description

    This quiz covers the fundamental principles of refraction and the importance of comprehensive case history in low vision rehabilitation. It highlights key considerations for practitioners when interacting with patients and conducting assessments. Understanding the psychological and medical aspects is crucial for effective patient care.

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