Optics Flashcards by Vanessa Racal

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.

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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.

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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.

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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.

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Fill in the blank: A real object presented to a _______ lens will always produce a virtual, upright, and smaller image.

negative

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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

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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, upright or inverted images depending on the object’s position relative to the focal point.

Object between 1st focal point & lens = virtual, upright, magnified image
Object placed to the left of 1st focal point = real, inverted, magnified image

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What is the wavelength range of UV-A light?

315-380 nm

UV-A is the longest of the three types of UV light.

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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.

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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.

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What is the wavelength range of UV-B light?

280-315 nm

Overexposure to UV-B can lead to sunburn.

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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.

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What is the wavelength range of UV-C light?

100-280 nm

UV-C has a shorter wavelength and is high-energy.

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What condition can prolonged exposure to UV-C lead to?

Solar keratitis

The majority of UV-C light is absorbed by the ozone layer.

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Which part of the eye absorbs the majority of UV-C light?

The cornea

The cornea protects the eye from UV-C exposure.

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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.

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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.

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How much light is needed in order to trigger a single molecule of rhodopsin?

1 quanta of light (smallest amount of light possible)

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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

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Which astigmatic dial is fixed?

Clock dial
* Target is not mobile

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What is the most common complication of RGPs?

3-9 staining (peripheral corneal desiccation)

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What is the most common complication associated with rigid gas permeable contact lens wear?

Peripheral corneal desiccation, also known as 3-9 staining

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What symptoms do patients typically report with peripheral corneal desiccation?

Mild symptoms of interpalpebral redness and slight irritation

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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

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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 ## Footnote This tolerance applies to prevent significant visual distortion.

What was the ordered cylinder axis in the prescription?

042 ## Footnote The cylinder axis indicates the orientation of the lens correction.

What was the verified cylinder axis in the prescription?

045 ## Footnote This discrepancy exceeds the ANSI tolerance for cylinder axis.

Does the cylinder axis difference of 3 degrees meet ANSI standards?

No ## Footnote The difference exceeds the permissible tolerance of 2 degrees.

What is the meridian of the highest absolute power in the prescription?

axis 135 ## Footnote This axis indicates where the lens power is strongest.

What is the power at the meridian of highest absolute power?

-15.50 D ## Footnote This value represents the maximum lens correction needed.

What was the sphere power sent from the lab?

-15.25 D ## Footnote 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 ## Footnote 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 ## Footnote This tolerance helps ensure adequate visual correction.

Does the difference of 0.25 meet the ANSI standards for sphere powers?

Yes ## Footnote 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 ## Footnote This tolerance ensures that the cylinder power is accurate for effective vision correction.

Did the above prescription meet ANSI standards for cylinder power?

Yes ## Footnote 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 ## Footnote 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 ## Footnote The amount of heat can also vary depending on the material.

What material requires high amounts of heat to insert lenses?

Optyl ## Footnote Optyl can bend under its own weight when heated properly.

At what temperature can Optyl material be safely heated?

100-130 degrees Celsius ## Footnote 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 ## Footnote 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 ## Footnote 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 ## Footnote This is crucial to avoid issues during lens insertion.

True or False: All plastic frame materials require heat for lens insertion.

False ## Footnote Some materials can use cold snapping, while others require heat.

True or false BIO has a smaller magnification, larger field of view and an inverted real image

True

Direct ophthalmoscope features what kind of image?

Upright virtual image

What is chromatic aberration?

A type of distortion in which a lens is unable to focus all wavelengths of light on the same convergence point.

What causes chromatic aberration?

The variation of the refractive index of any medium with wavelength.

Which wavelengths bend more as they pass through a lens?

Shorter wavelengths (blues).

Which wavelengths bend less as they pass through a lens?

Longer wavelengths (reds).

What are the two types of chromatic aberration?

* Longitudinal chromatic aberration * Lateral chromatic aberration

During subjective refraction, where should the retina be centered?

Between the image point for the shorter and longer wavelengths.

What test is used to balance the image points for different wavelengths?

The Red-Green test.

If a patient reports clearer letters on the red side of the Red-Green test, what does this indicate?

The center point is too far in front of the retina.

What is the recommended lens adjustment if the red side is clearer?

A minus lens will improve this balance (Red Add Minus-RAM).

If a patient reports sharper letters on the green side of the Red-Green test, what does this indicate?

The center point is too far behind the retina.

What is the recommended lens adjustment if the green side is sharper?

A plus lens will shift the balance (Green Add Plus-GAP).

The entire Red-Green test is dependent upon the principles of _______.

[chromatic aberration]

Which type of aberration is primarily responsible for results found using the Red-Green test when performing subjective refraction?

Chromatic aberration

4x Explanation: entering acuity divided by goal acuity 400/100 = 4x magnification

True or false When an object is located at half the focal length of the plus thin lens the object and image are the same size

FALSE * when the object is located TWICE the focal length of the plus thin lens the object and image size are the same

The “reduced eye” consists of a single spherical refracting surface that separates air and aqueous. What is the radius of curvature of the surface?

+5.55 mm * axial length of the reduced eye is 22.22 mm

Principal of univariance

Fact that once quatra are absorbed by rhodopsin, all of the information pertaining to the light (such as wavelength) is lost. Therefore if the photopigment rhodopsin is bleached, the wavelength does not matter because the final result will be equivalent

Purkinje shift

Shift in peak spectral sensitivities during the change from Scotopic to photopic vision. Means that as light increases, longer wavelengths appear brighter because the peak spectral sensitivity for Scotopic conditions is 507nm and 555nm for photopic vision.

Mesopic conditions

Both rods and cones function simultaneously, such as during twilight

Why is the retina referred to as being a duplex?

Because it possesses two separate groups of photoreceptors which function under different lighting conditions

Optics Flashcards

(76 cards)