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23 Cards in this Set
- Front
- Back
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Angular Mag Formula |
AM = qL/1 - dL' |
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Linear Mag |
M = L/L' h' = h x L/L' thick: h' = h x L1/L1' x L2/L2' |
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Nom and Max Mag |
F/4 F/4 +1 |
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Telescope Mag formula |
M = -Fe/Fo |
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Lens Cap and Total Mag |
Fcap/4 x -Fe/Fo |
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SI and SSI registration groups |
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Which form is used for the registration of SI and SSI pxs? |
Certificate of Vision Impairment (CVI) |
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Vergence arriving at the eye |
l2 = l1' - d 1/l2 = L2 |
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Advantages of dv telescopes |
Only realistic option for Dv mag Good depth of field Can be hands free Only practical solution for long inter wd Can be mono/bin Variable focus |
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Disadvantages of dv telescopes |
High cost Difficult to use Extensive training Very poor FOV Heavy Conspicuous device |
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Markings: 8x20x7.5 |
8 = magnification 20 = objective diameter 7.5 = field of view (°) |
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Rules of thumb |
Spec mounted mag: 1 base in for every dioptre of object to lens distance. For emmetrope, 1 base in for every dioptre
High add: 1 base in for every dioptre of addition over +3.00
High add bifocals: 1mm inset for every dioptre of addition |
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What is nominal Mag? |
Special case of angular mag Only achieved when object placed at 1st principle focus Image is formed at infinity |
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How can nominal mag be derived from angular mag principles? |
AM = qL/1-dL' l = f L = -F l' = infinity L' = 0 Mnom = -0.25 × -F/1 - (d x 0) Mnom = -0.25 x -F Mnom = F/4 |
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Benefits to being registered sight impaired |
Additional income support DLA or PIP Additional housing benefit or council tax allowance Provision of low vision aids 50% reduction in TV license fee Free NHS sight test Car park concessions Access to attendance allowance |
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10 members a DO can refer a px to to provide support |
Social services Social worker Therapist Rehabilitation officer Mobility officer Local low vision clinic Local charities Local council Diasbled employment advisor Educational advisory teams |
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What is luminous efficacy? |
The measure of how well a light source produces visible light |
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Define Luminous intensity, luminous flux and illuminance and state a unit for each |
Luminous intensity is the strength of a light source in a given direction and is measured in candela (cd) Luminous flux is the rate of flow of light energy from a source and is measured in lumens (lm) Illuminance is the measure of the luminous flux density at a point on a surface and is measured in lux. |
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Define Luminous intensity, luminous flux and illuminance and state a unit for each |
Luminous intensity is the strength of a light source in a given direction and is measured in candela (cd) Luminous flux is the rate of flow of light energy from a source and is measured in lumens (lm) Illuminance is the measure of the luminous flux density at a point on a surface and is measured in lux. |
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Angular Mag thick lenses |
qL1L2/L1' x (1-dL2') |
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Define terms linear mag and angular mag |
Linear mag: given by m = height of image/height of object = h'/h Angular mag: AM = angle subtended at eye by virtual image/angle subtended at unaided eye by object at RSD |
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What is maximum mag? |
When the image formed by the magnifier lies at the RSD and the eye to lens distance is zero |
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FE formula (thick lenses) |
FE = F1 + F2 - t/n x F1 x F2 |
