NAO TEST 4 | 100 QUESTIONS AND ANSWERS WITH VERIFIED
SOLUTIONS | LATEST UPDATE 2025
Question 1
Which statement correctly describes light waves that are less than 20 feet from their source?
A) They are considered parallel.
B) They are considered converging.
C) They are considered diverging.
D) They are considered collimated.
Correct Answer: C) they are considered diverging
Rationale: Light originating from a point source travels outward in all directions. At a close
distance (conventionally considered less than 20 feet or 6 meters), these light rays are still
spreading apart, or diverging, as they reach the observer. Light from a source beyond 20
feet is considered to be effectively parallel.
Question 2
What is the range of visible light wavelengths to which the human eye is sensitive?
A) 200-400 nm
B) 380-760 nm
C) 760-900 nm
D) 100-1000 nm
Correct Answer: B) 380-760 nm
Rationale: The visible spectrum of light for humans is a narrow band of electromagnetic
radiation. Wavelengths shorter than this range are ultraviolet (UV), and wavelengths
longer than this range are infrared (IR). The accepted range for visible light is
approximately 380 to 760 nanometers.
Question 3
When light encounters the surface of an ophthalmic lens, which of the following interactions
occurs to the greatest degree?
A) Reflected
B) Absorbed
C) Transmitted
D) Scattered
Correct Answer: C) transmitted
Rationale: Ophthalmic lenses are designed to be transparent and allow the maximum
amount of light to pass through them to the eye. While some light is always reflected and a
small amount is absorbed, the vast majority of the light is transmitted through the lens.
Question 4
A standard CR-39 plastic lens has a refractive index of approximately 1.498. How much light
does a single surface of this lens reflect?
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A) 1.5%
B) 4.0%
C) 8.1%
D) 10.0%
Correct Answer: B) 4.0%
Rationale: The amount of reflection from a single surface can be calculated using Fresnel's
equation. For a standard 1.498 index lens, the reflection per surface is approximately
4%. Correction: The source material asks how much a 1.49 index lens reflects, with an answer
of 8.1%. This implies the question is asking for the total reflection from both surfaces (approx.
4% from the front + 4% from the back).
Question 4 (Revised)
How much total light does a standard uncoated 1.49 index lens reflect?
A) 4.0%
B) 6.2%
C) 8.1%
D) 12.5%
Correct Answer: C) 8.1%
Rationale: A standard CR-39 lens reflects approximately 4% of light from its front surface
and another 4% from its back surface. The total amount of light reflected is approximately
8.1%, which means only about 92% of the available light reaches the eye.
Question 5
Anti-reflective (AR) treatments on eyeglass lenses are based upon what optical characteristic?
A) Destructive interference
B) Constructive interference
C) Total internal reflection
D) Polarization
Correct Answer: A) destructive interference
Rationale: An AR coating consists of multiple thin layers of metallic oxides. The thickness
of these layers is precisely controlled so that the light waves reflecting off the coating
surface are out of phase with the light waves reflecting off the lens surface. This causes the
waves to cancel each other out, a phenomenon known as destructive interference, which
eliminates the reflection.
Question 6
Light that reflects off the front and back surfaces of a lens, creating ghost images and halos, is an
example of which type of glare that an AR treatment eliminates?
A) Discomforting glare
B) Disabling glare
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C) Blinding glare
D) Distracting glare
Correct Answer: D) distracting
Rationale: Distracting glare is caused by light reflections off the lens surfaces themselves.
These reflections can appear as ghost images or halos (especially at night) and can be very
annoying to the wearer. AR coatings are specifically designed to eliminate this type of glare.
Question 7
Which type(s) of UV radiation are a primary cause of sunburn (erythema)?
A) UVA only
B) UVB only
C) UVC only
D) Both UVA and UVB
Correct Answer: D) Both UVA and UVB
Rationale: UVB is the primary cause of sunburn, damaging the skin's outer layers.
However, UVA radiation penetrates deeper into the skin and also contributes to sun
damage and tanning, which is a sign of skin cell damage.
Question 8
A superficial, painful inflammation of the cornea, often caused by intense UV exposure (like
"snow blindness"), is known as:
A) A cataract
B) Photokeratitis
C) A pterygium
D) Macular degeneration
Correct Answer: B) photokeratitis
Rationale: Photokeratitis is essentially a sunburn of the cornea. It is a painful condition
caused by overexposure to UV radiation, either from the sun (especially when reflected off
snow or water) or from artificial sources like welding arcs.
Question 9
Which of the following eye conditions, linked to cumulative UV exposure, is a leading cause of
blindness worldwide?
A) Glaucoma
B) Diabetic Retinopathy
C) Age-Related Macular Degeneration (ARMD)
D) Retinal detachment
Correct Answer: C) ARMD
Rationale: Age-related macular degeneration is a progressive disease that affects the
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central part of the retina (the macula). While its causes are multifactorial, long-term
exposure to UV and blue light is considered a significant risk factor.
Question 10
Which portion of the UV spectrum is mostly absorbed by the crystalline lens of the adult eye?
A) UVC
B) UVB
C) UVA
D) All UV is absorbed by the cornea.
Correct Answer: C) UVA
Rationale: The eye's natural structures provide some UV protection. The cornea absorbs
most UVC and a large portion of UVB. The crystalline lens then absorbs most of the
remaining UVA radiation, which helps to protect the retina. However, this absorption
contributes to the formation of cataracts over time.
Question 11
In a child under the age of 10, how much UV radiation passes through their clear crystalline lens
and reaches the retina?
A) Less than 1%
B) About 10%
C) About 25%
D) About 75%
Correct Answer: D) 75%
Rationale: A child's crystalline lens is much clearer than an adult's and has not yet
developed the natural yellowing that helps to filter UV radiation. As a result, a significantly
higher percentage (up to 75%) of UV radiation can pass through and reach the delicate
retinal tissue, making UV protection for children critically important.
Question 12
Which sunlens color is known for providing excellent contrast and improving visual acuity and
depth perception, making it popular for activities like golf and tennis?
A) Gray
B) Green
C) Bronze/Brown
D) Yellow
Correct Answer: C) Bronze/Brown
Rationale: Brown and bronze tints are contrast-enhancing. They do this by selectively
filtering out blue light, which reduces haze and improves the distinction between colors,
particularly against green (grass) and blue (sky) backgrounds.
SOLUTIONS | LATEST UPDATE 2025
Question 1
Which statement correctly describes light waves that are less than 20 feet from their source?
A) They are considered parallel.
B) They are considered converging.
C) They are considered diverging.
D) They are considered collimated.
Correct Answer: C) they are considered diverging
Rationale: Light originating from a point source travels outward in all directions. At a close
distance (conventionally considered less than 20 feet or 6 meters), these light rays are still
spreading apart, or diverging, as they reach the observer. Light from a source beyond 20
feet is considered to be effectively parallel.
Question 2
What is the range of visible light wavelengths to which the human eye is sensitive?
A) 200-400 nm
B) 380-760 nm
C) 760-900 nm
D) 100-1000 nm
Correct Answer: B) 380-760 nm
Rationale: The visible spectrum of light for humans is a narrow band of electromagnetic
radiation. Wavelengths shorter than this range are ultraviolet (UV), and wavelengths
longer than this range are infrared (IR). The accepted range for visible light is
approximately 380 to 760 nanometers.
Question 3
When light encounters the surface of an ophthalmic lens, which of the following interactions
occurs to the greatest degree?
A) Reflected
B) Absorbed
C) Transmitted
D) Scattered
Correct Answer: C) transmitted
Rationale: Ophthalmic lenses are designed to be transparent and allow the maximum
amount of light to pass through them to the eye. While some light is always reflected and a
small amount is absorbed, the vast majority of the light is transmitted through the lens.
Question 4
A standard CR-39 plastic lens has a refractive index of approximately 1.498. How much light
does a single surface of this lens reflect?
,[Type here]
A) 1.5%
B) 4.0%
C) 8.1%
D) 10.0%
Correct Answer: B) 4.0%
Rationale: The amount of reflection from a single surface can be calculated using Fresnel's
equation. For a standard 1.498 index lens, the reflection per surface is approximately
4%. Correction: The source material asks how much a 1.49 index lens reflects, with an answer
of 8.1%. This implies the question is asking for the total reflection from both surfaces (approx.
4% from the front + 4% from the back).
Question 4 (Revised)
How much total light does a standard uncoated 1.49 index lens reflect?
A) 4.0%
B) 6.2%
C) 8.1%
D) 12.5%
Correct Answer: C) 8.1%
Rationale: A standard CR-39 lens reflects approximately 4% of light from its front surface
and another 4% from its back surface. The total amount of light reflected is approximately
8.1%, which means only about 92% of the available light reaches the eye.
Question 5
Anti-reflective (AR) treatments on eyeglass lenses are based upon what optical characteristic?
A) Destructive interference
B) Constructive interference
C) Total internal reflection
D) Polarization
Correct Answer: A) destructive interference
Rationale: An AR coating consists of multiple thin layers of metallic oxides. The thickness
of these layers is precisely controlled so that the light waves reflecting off the coating
surface are out of phase with the light waves reflecting off the lens surface. This causes the
waves to cancel each other out, a phenomenon known as destructive interference, which
eliminates the reflection.
Question 6
Light that reflects off the front and back surfaces of a lens, creating ghost images and halos, is an
example of which type of glare that an AR treatment eliminates?
A) Discomforting glare
B) Disabling glare
,[Type here]
C) Blinding glare
D) Distracting glare
Correct Answer: D) distracting
Rationale: Distracting glare is caused by light reflections off the lens surfaces themselves.
These reflections can appear as ghost images or halos (especially at night) and can be very
annoying to the wearer. AR coatings are specifically designed to eliminate this type of glare.
Question 7
Which type(s) of UV radiation are a primary cause of sunburn (erythema)?
A) UVA only
B) UVB only
C) UVC only
D) Both UVA and UVB
Correct Answer: D) Both UVA and UVB
Rationale: UVB is the primary cause of sunburn, damaging the skin's outer layers.
However, UVA radiation penetrates deeper into the skin and also contributes to sun
damage and tanning, which is a sign of skin cell damage.
Question 8
A superficial, painful inflammation of the cornea, often caused by intense UV exposure (like
"snow blindness"), is known as:
A) A cataract
B) Photokeratitis
C) A pterygium
D) Macular degeneration
Correct Answer: B) photokeratitis
Rationale: Photokeratitis is essentially a sunburn of the cornea. It is a painful condition
caused by overexposure to UV radiation, either from the sun (especially when reflected off
snow or water) or from artificial sources like welding arcs.
Question 9
Which of the following eye conditions, linked to cumulative UV exposure, is a leading cause of
blindness worldwide?
A) Glaucoma
B) Diabetic Retinopathy
C) Age-Related Macular Degeneration (ARMD)
D) Retinal detachment
Correct Answer: C) ARMD
Rationale: Age-related macular degeneration is a progressive disease that affects the
, [Type here]
central part of the retina (the macula). While its causes are multifactorial, long-term
exposure to UV and blue light is considered a significant risk factor.
Question 10
Which portion of the UV spectrum is mostly absorbed by the crystalline lens of the adult eye?
A) UVC
B) UVB
C) UVA
D) All UV is absorbed by the cornea.
Correct Answer: C) UVA
Rationale: The eye's natural structures provide some UV protection. The cornea absorbs
most UVC and a large portion of UVB. The crystalline lens then absorbs most of the
remaining UVA radiation, which helps to protect the retina. However, this absorption
contributes to the formation of cataracts over time.
Question 11
In a child under the age of 10, how much UV radiation passes through their clear crystalline lens
and reaches the retina?
A) Less than 1%
B) About 10%
C) About 25%
D) About 75%
Correct Answer: D) 75%
Rationale: A child's crystalline lens is much clearer than an adult's and has not yet
developed the natural yellowing that helps to filter UV radiation. As a result, a significantly
higher percentage (up to 75%) of UV radiation can pass through and reach the delicate
retinal tissue, making UV protection for children critically important.
Question 12
Which sunlens color is known for providing excellent contrast and improving visual acuity and
depth perception, making it popular for activities like golf and tennis?
A) Gray
B) Green
C) Bronze/Brown
D) Yellow
Correct Answer: C) Bronze/Brown
Rationale: Brown and bronze tints are contrast-enhancing. They do this by selectively
filtering out blue light, which reduces haze and improves the distinction between colors,
particularly against green (grass) and blue (sky) backgrounds.
