13984519
| Pregunta | Respuesta |
| Presbyopia | Definition: Difficulty with near work due to lens inflexibility with age, resulting from decrease ability to accommodate Accommodative state: lost ability to accommodate Optical basis: Biological basis: lens become harder - cannot be stretched |
| Emmetropia | Definition: Conjugate focus of the retina is at infinity (-0.25 to +0.75DS) Accommodative state: accomodation is relaxed at infinity Optical basis: Biological basis: |
| Myopia | Definition: Distant objects are focused in front of the retina while near objects viewed at the far point by accommodation (</= -0.50 DS) Accommodative state: accommodating at infinity Optical basis: corneal power is too strong Biological basis: eye has grown too long |
| Hypermetropia/hyperopia | Definition: Distance objects are focused behind the photoreceptors when accommodation is relaxed (>/= +0.75) Accommodative state: increase accommodation for objects at near Optical basis: Corneal power is not strong enough Biological basis: Eye is too short |
| Astigmatism | Definition: Image of a point object is not a single point but two perpendicular lines at different distances from the optical system Optical basis: toroidal refracting surfaces of the eye Biological basis: corneal surface is uneven |
| Interpret a spectacle prescription | +/- spherical power DS / - cyl power DC x axis |
| Define pupillary distance and state its importance | Distance between the two corneal reflex of the left and right eye. Importance: changes when viewing at distance and viewing at near * important for when putting prescription into spectacles |
| Prevalence of emmetropia and ametropia | Prevalence of emmetropia: * ~60% in 40-90yrs Prevalence of ametropia: differs by age, genetics and environmental circumstances * Children - eye is smaller (more hypermetropic but can accommodate to achieve (91%) * Australian population myopic = ~20% |
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