Optics Flashcards
What type of image does a negative lens produce when a real object is presented?
A virtual, upright, and smaller image
This holds true regardless of whether the object is placed in front of or behind the first focal point.
What is the function of field-expanding lenses, such as Fresnel lenses?
To enhance the field of view in applications like rear windows of vans or RVs
Fresnel lenses are designed to reduce the amount of material required while maintaining optical performance.
What type of image is produced when a real object is placed between the first focal point and a plus lens?
A virtual, upright, enlarged image
This principle is the basis for single lens magnifiers.
What type of image does a plus lens produce when a real object is placed to the left of the first focal point?
A real, inverted image
This principle is foundational for imaging systems such as the eye, camera, and projector.
Fill in the blank: A real object presented to a _______ lens will always produce a virtual, upright, and smaller image.
negative
Fill in the blank: The basis for single lens magnifiers is when a real object is placed between the first focal point and a _______ lens.
plus
True or False: A plus lens will always produce an upright image regardless of the object’s position.
False
A plus lens can produce both real and virtual images depending on the object’s position relative to the focal point.
What is the wavelength range of UV-A light?
315-380 nm
UV-A is the longest of the three types of UV light.
How does UV-A radiation compare to other types of UV light in terms of damage?
Considered the least damaging
UV-A penetrates deeper into the skin.
Which type of UV light is more abundant at the Earth’s surface?
UV-A radiation
UV-A is much more abundant than UV-B and UV-C.
What is the wavelength range of UV-B light?
280-315 nm
Overexposure to UV-B can lead to sunburn.
What health issues are associated with UV-B exposure?
Sunburn, skin cancer, cataract formation
UV-B has a higher correlation with these issues than UV-A.
What is the wavelength range of UV-C light?
100-280 nm
UV-C has a shorter wavelength and is high-energy.
What condition can prolonged exposure to UV-C lead to?
Solar keratitis
The majority of UV-C light is absorbed by the ozone layer.
Which part of the eye absorbs the majority of UV-C light?
The cornea
The cornea protects the eye from UV-C exposure.
What absorbs the majority of UV-A and UV-B light in the eye?
The crystalline lens
This protects the retina from potential UV damage.
What can occur over time to the lens of the eye as a result of UV exposure?
Formation of a cataract
The lens may become impaired over time.
How much light is needed in order to trigger a single molecule of rhodopsin?
1 quanta of light (smallest amount of light possible)
As the power of a condensing lens increases what happens to the FOV, magnification and working distance?
Increase in power = increase FOV, decrease in mag and decrease in working distance
Ex: 90 D vs 78 D lens
Which astigmatic dial is fixed?
Clock dial
* Target is not mobile
What is the most common complication of RGPs?
3-9 staining (peripheral corneal desiccation)
What is the most common complication associated with rigid gas permeable contact lens wear?
Peripheral corneal desiccation, also known as 3-9 staining
What symptoms do patients typically report with peripheral corneal desiccation?
Mild symptoms of interpalpebral redness and slight irritation
What does a slit lamp examination reveal in cases of peripheral corneal desiccation?
Superficial punctate staining that can vary from small to larger coalescing areas of SPK, with deep fluorescein staining
What is dellen formation associated with in contact lens wear?
Deep fluorescein staining
What causes the signs of peripheral corneal desiccation?
Excessive edge lift of the contact lenses leading to tear film disruption
How can the signs and symptoms of peripheral corneal desiccation be minimized?
Adjustments to the fit of the contact lenses to decrease edge lift and increase lid apposition
What adjustments can be made to achieve better fit and minimize symptoms?
Steepening the base curve and/or steepening the peripheral curves of the contact lens
What additional modifications can help minimize peripheral corneal desiccation?
Thinning the contact lens edge and lenticulating higher minus lenses
Is changing the material of the lens beneficial in reducing corneal signs related to 3-9 staining?
No, studies have shown it has no benefit
True or False: 3-9 staining is purely fit related.
True
How to calculate JND?
Divide denominator by 100
Ex: 20/400
400/100 =4
With trial frame show +2.00 and -2.00 lenses
What is the ANSI standard tolerance for cylinder axis of prescriptions with a cylinder power of 1.75 diopters or greater?
2 degrees in any direction
This tolerance applies to prevent significant visual distortion.
What was the ordered cylinder axis in the prescription?
042
The cylinder axis indicates the orientation of the lens correction.
What was the verified cylinder axis in the prescription?
045
This discrepancy exceeds the ANSI tolerance for cylinder axis.
Does the cylinder axis difference of 3 degrees meet ANSI standards?
No
The difference exceeds the permissible tolerance of 2 degrees.
What is the meridian of the highest absolute power in the prescription?
axis 135
This axis indicates where the lens power is strongest.
What is the power at the meridian of highest absolute power?
-15.50 D
This value represents the maximum lens correction needed.
What was the sphere power sent from the lab?
-15.25 D
This is the measured power compared against the prescribed power.
What is the difference between the prescribed power and the lab’s power?
0.25
This difference is crucial for determining compliance with ANSI standards.
What is the ANSI tolerance for sphere powers above 6.50 D?
+/- 2% of the power
This tolerance helps ensure adequate visual correction.
Does the difference of 0.25 meet the ANSI standards for sphere powers?
Yes
0.31 is allowed (2% of 15.50 D), and 0.25 is within this limit.
What is the ANSI standard for error tolerance in cylinder power for cylinder powers of 2.25 to 4.50 D?
+/- 0.15 D
This tolerance ensures that the cylinder power is accurate for effective vision correction.
Did the above prescription meet ANSI standards for cylinder power?
Yes
There was no difference between what was ordered and what was measured.
What is the equivalent logMAR acuity of 20/60?
0.48
explanation: take reciprocal of decimal acuity
20/60 =0.333
Now take the log of the reciprocal
Log(1/0.333)=0.478
Make sure you know how to calculate!!
What is the process called when lenses are inserted into frames without using heat?
Cold snapping
This method is used for certain frame materials that do not require heat.
What is a major variant in the lens insertion process for plastic frames?
Whether or not heat is used
The amount of heat can also vary depending on the material.
What material requires high amounts of heat to insert lenses?
Optyl
Optyl can bend under its own weight when heated properly.
At what temperature can Optyl material be safely heated?
100-130 degrees Celsius
Heating beyond this range may damage the material.
Which materials utilize only minimal amounts of heat if lenses cannot be cold snapped?
- Cellulose acetate
- Cellulose proprionate
- Carbon fiber
These materials may allow for some heat but not extensive heating.
What should not be done to polycarbonate and polyamide materials during lens insertion?
They should not be heated at all
Heating these materials can lead to warpage.
What is required for edged lenses when using polycarbonate and polyamide materials?
They must be fabricated exactly to size
This is crucial to avoid issues during lens insertion.
True or False: All plastic frame materials require heat for lens insertion.
False
Some materials can use cold snapping, while others require heat.
