Flashcards in Optics Deck (19)
What does an ideal "wave plate" do? What does it NOT do?
Wave plates do NOT reflect or absorb light. The transmittance should be 100%.
Wave plates change the PHASE SHIFT of light
What happens to the retinoscopy light reflex as it approaches neutrality?
Becomes BROADER, faster, and brighter.
What is Mohindra Retinoscopy?
Retinoscopy done on a child that you cannot dilate. Occlude one eye and ret the other. Use a working distance of -1.25.
What is the power of a plane mirror?
PLANE mirrors have NO POWER
How tall is a 20/20 Snellen optotype at 20 feet?
How tall is a 1M optotype at 1 M?
Snellen = 8.73 mm
1M = 1.45 mm
For every 1mm increase in axial length there is a ____ increase in myopia
1mm increase in axial length = -3.00D of myopia
Define entrance pupil
The IMAGE of the aperture stop by the PRECEDING lenses
According to ANSI standards, what can patients tolerate in sphere? Cyl axis?
Sphere: Below 6.50 D -> ± 0.13D
Above 6.50 D -> 2% of D
Cyl: Above 1.50 D -> ± 2°
What three improvements do aspheric lenses make?
Reduce spherical aberration
Point-focal lenses correct _______
Percival lenses correct ______
Point-focal lenses correct RESIDUAL ASTIGMATISM
Percival lenses correct CURVATURE OF FIELD
What are the only two parameters you need to solve image jump problems?
1. Add power
2. Segment height
What spectacle parameters will increase spectacle mag?
Increasing base curve
Increasing center thickness
Increasing vertex distance
What is the relationship between Dk and water in traditional soft lenses? Silicone Hydrogels?
Traditional - High water content -> High Dk
Silicone Hydrogel - Higher water content -> Low Dk
What percent of the population is an emmetrope / low hyperope?
What type of astigmatism is associated with the development of myopia?
What property of light does not change when traveling from one medium to another? What properties do change?
Frequency does NOT change
Wavelength and Speed DO change
What is the difference between Gross and Net Retinoscopy?
Gross - Through the ret rack
Net - Calculated with working distance
Convex mirrors typically have a negative or positive power?