Questions and Answers
What happens to the lens with age?
At what age does the lens typically lose all accommodative ability?
What determines the near addition prescribed for presbyopia?
Why does the image fall behind the retina in presbyopia?
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What is the result of the ciliary muscle contracting with the same amount of force as it ages?
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What is the relationship between the refractive state of the patient and presbyopia?
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When does the process of presbyopia typically begin?
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What is the accommodative demand of near tasks in diopters when focusing at 40cm?
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What happens to the zonules when the ciliary muscle contracts?
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Study Notes
Refractive Errors Overview
- Emmetropia: Light is focused correctly on the retina for clear distance vision; near tasks require accommodation to maintain clarity.
- Myopia (Short-Sightedness): Results from an elongated eye or high power, causing light to focus in front of the retina, leading to blurry distance vision. Corrected with concave lenses.
- Hyperopia (Long-Sightedness): Due to a shorter eye or weak power, causing light to focus behind the retina. Generally asymptomatic in mild cases but corrected with convex lenses.
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Astigmatism: Defined by two focal points due to uneven curvature of the cornea or retina, categorized into:
- With-the-rule
- Against-the-rule
- Oblique
- Irregular
Mechanism of Emmetropisation
- Emmetropisation: A process where the eye adjusts to focus light appropriately on the retina, failing can result in long-term refractive errors like hyperopia.
Accommodation Mechanism
- Accommodation involves the lens changing shape to focus on near objects; declines with age, affecting visually demanding tasks, especially in presbyopia.
- Decline in accommodation linked to lens elasticity loss with aging, becoming apparent around age 40.
Clinical Presentation of Refractive Errors
- Myopia: Clear near vision but blurred distance vision; the degree of myopia determines the distance of clear sight.
- Hyperopia: Difficulty with near tasks, may appear asymptomatic until accommodation strain occurs.
- Presbyopia: Affects near vision due to decreased accommodation ability, leads to a need for near addition lenses.
Myopia Progression and Management
- Average myopia progression recorded in studies is between 0.55 ± 0.86D to 1.12 ± 0.85D over two years.
- Atropine treatment shows dose-dependent effectiveness in controlling myopia progression; recommended dosages are 0.05% and 0.025%, balancing efficacy and side effects.
- Orthokeratology (Ortho K): Special lens therapy that reshapes the cornea overnight to control myopia, shown to reduce axial length by 43%-63%.
Consequences of Uncorrected Hyperopia
- Children with high hyperopia risk developmental issues; may lead to amblyopia if not corrected early.
- Excessive accommodation can lead to esophoria, causing visual strain and inefficiencies in maintaining clear vision.
Management of Presbyopia
- Requires a near addition after assessing distance prescription and considering the patient’s near task demands and accommodation reserves.
- Typical near tasks necessitate a prescription adjustment based on estimated accommodative needs, e.g., for a distance vision of +2.5D when focusing at ~40cm.
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Description
This quiz covers the basics of optics, including hyperopia, myopia, astigmatism, and presbyopia, as well as the mechanisms of emmetropisation, accommodation, and the clinical presentation of refractive errors.
