Basic optometry readings
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34 terms
Terms | Definitions |
|---|---|
 Accommodation | The process whereby changes in the dioptric power of the crystalline lens occur so that an in focus image of the object is obtained and maintained on the fovea |
| Descartes | Proposed lenticular based focusing |
| Thomas Young | Demonstrated changes in the crystalline lens were responsible for focusing changes |
| Hermann von Helmholtz | Considered the father of physiologic optics. Advanced the first basic and reasonably accurate explanation of the accommodative process. |
| Ideas proposed for how we see clearly at different distances: | 1) There is no need for an active form of focusing 2) Pupil size changes with the effort to see clearly at near 3) Corneal curvature changes with a change in focal point 4) The anteroposterior position of the lens changes with variation in focal point 5) Changes in the axial length of the eyeball itself account for shifts in the position of the retinal image for objects at varying distances 6) Changes in the shape, and therefore power, of the crystalline lens allow objects at various distances to be focused on the retina -> correct description of accommodation |
| Reflex accommodation | The automatic adjustment of refractive state to obtain and maintain a sharply defined and focused retinal image in response to blur input. |
| Accommodation occurs when? | Ciliary muscle constricts -> choroid and posterior zonules stretch -> anterior zonules reduce their tension and relax -> elastic forces cause the crystalline lens becomes more spherical (increasing its dioptric power) |
| The profile of the accommodative response | 1) Linear manifest zone - change in accomm stimulus produces proportional change in accomm response 2) Initial Nonlinear zone 3) Nonlinear Transition zone 4) Nonlinear Latent zone 5) Myopic Nonlinear Defocus zone 6) Hyperopic Nonlinear Defocus region |
| Crystalline lens is? | A bi-convex structure between the iris and viterous, whose function is to focus light |
| Suspension Ligament | Holds the crystalline lens in position and enables the ciliary muscle to act on the lens |
| Optical cues that influence accommodation | Chromatic aberration Spherical aberration Astigmatism Microfluctuations Blur asymmetry due to fixational eye movements |
| Nonoptical cues that influence accommodation | Size Proximity Apparent distance Disparate retinal images Monocular depth cues |
| Nonretinal influences on accommodation | Vestibular stimulation Training/therapy Mood Prediction Voluntary effort Cognitive demand Visual imagery Instruction set |
| Retinal influences on accommodation | Spatial frequency Contrast Retinal eccentricity Retinal-image motion Luminance Size Depth of focus Disparity-driven vergence accommodation |
| The stimulus to accommodation is? | blur |
| photorefraction | An objective way to estimate refractive error |
| Purkinjie-Sanson images | Specular reflections that occur at the interfaces between the transparent media of the eye |
| The major specular reflection that interferes with objective refraction is? | the corneal reflex |
| The two components of light reflected from the fundus | 1) diffuse component (backscatter) 2) directed component |
| The most significant sources of diffuse visible light are? | Retinal Pigment Epithelium and choroid RPE- contains melanin capillary net directly behind RPE- Hemoglobin Contribute to red/orange color of fundus reflex |
| The retinal surface responsible for detection of the image during subjective refraction is the? | outer limiting membrane |
| Punctum remotum is? | The far point that is optically conjugate to the fovea when accommodation is relaxed. Myopes - PR is anterior to the eye Hyperopes - PR is posterior to the eye |
| With motion of the pupillary streak indicates a PR located? | behind the retinoscope (behind the examiner's eye) OR behind the patient's eye |
| a PR behind the examiner's eye indicates a patient which could be? | Hyperopic Low myopic Emmetropic |
| Against motion of the pupillary streak indicates a PR located? | Between the retinoscope (examiner's eye) and the patient's eye. Only seen with moderate to high myopes |
| If the examiner observes with motion, neutrailty can be achieved by? | Either adding plus lenses or by moving further away from the patient (approaching the punctum remotum). |
| If the retinoscope reflex if at neutrality, the far point is located? | at the aperture of the retinoscope |
| If the PR is behind the examiner's eye, what is the refractive error? | Low myope |
| If the PR is behind the patient's eye, what is the refractive error? | Hyperope |
| If the eye is emmetropic? | Light from retinoscope focuses behind the retina Light reflected from the eye focuses behind the retinoscope With motion is observed |
| If the eye is hyperopic? | Light from retinoscope focuses behind the retina Light reflected from the eye focuses behind the retinoscope With motion is obeserved |
| If the eye is moderate to high myopic? | Light from retinoscope focuses before the retina Light reflected from the eye focuses before the retinoscope Against motion is observed |
| Plane mirror mode | Barrel down The apparent light source is behind the retinoscope Divergent light leaves the retinoscope Streak inside the eye moves same as streak on iris (ex: you tilt the retinoscope down the out-of-focus patch of light on the patient's retina moves down) |
| Concave mirror mode | The apparent light source is between the retinoscope and the patient's eye When the retinoscope is tilted down the out-of-focus patch of light on the patient's retina moves up |
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