Week 1: Introduction of Optics

Question 1

Describe conjugate planes and list the formula

Answer 1

• Whole object & its image are at CONJUGATE PLANES
• Conjugate Foci Formula; L + F = L’

Question 2

Describe spherical lens

Answer 2

• brings parallel light to a single point focus

Question 3

Describe cylindrical lenses

Answer 3

refract light in one meridian whilst leaving light unrefracted in perpendicular meridian

Question 4

Describe axis meridian

Answer 4

Meridian along which parallel rays will not be refracted

Question 5

Describe power meridian

Answer 5

Meridian along which there is maximum refraction of light. This lies at 90 degrees to axis meridian

Question 6

What is refractive state?

Answer 6

with respect to infinity and the eye is in its UNACCOMMODATED state

Question 7

Describe emmetropia

Answer 7

A distant object is conjugate with the eye’s optical system on the retina

Question 8

Describe ametropia

Answer 8

A distant object is not imaged by the eye’s optical system on the retina

Question 9

What are the types of spherical ametropia?

Answer 9

• Axial
• Refractive: index, curvature, position of an element, absence of an element

Question 10

What is Sphero-Cylindrical Lenses?

Answer 10

Rays are refracted in both meridians, just in differing amounts

Question 11

What is myopia?

Answer 11

• Distance blurry, with near clear
• Eye has a normal axial length, but has too much refractive power
  -The eye has the normal amount of refractive power, but axial length is too large
• Far point plane (MR) is located in front of the eye

Question 12

What is hyperopia

Answer 12

• Eye is limited by how much accommodation it can exert, and for how long it can exert this accommodation
• The far point plane is located behind the principle plane of the eye (imaginary plane)

Question 13

What is Astigmatism?

Answer 13

• A refractive condition by which the refractive power in one meridian differs to that of the other meridian
• Eye is incapable of bringing light to a point focus and instead creates two perpendicular line foci separated in distance
• Can treat the meridians separately, hence the astigmatism can be; myopic, hyperopic & mixed

Question 14

What is presbyopia?

Answer 14

• As we age, crystalline lens is continuously becoming more rigid, making it more difficult to exert accommodation
• By the age of 40-45, the amount of accommodation loss means that there is no longer sufficient accommodative power to form a clear image of close objects

Question 15

List 3 lens types?

Answer 15

• Single vision
• Bifocals/trifocals = multifocals
• Progressives = PALs

Question 16

What are single vision lenses?

Answer 16

Are simple lenses designed to enable clear vision throughout the whole of the lens

Question 17

What are meniscus lenses?

Answer 17

• Lenses that we use in spectacles are meniscus lenses
• These lenses enable us to both;
  • Improve the aesthetics of spectacle lenses
  •Decrease the aberrations that we notice when looking through the lens
• Meniscus lenses have a convex anterior surface & a concave posterior surface
• Positive, negative, and astigmatic lenses can all be of meniscus design

Question 18

What are multifocals?

Answer 18

• These are lenses in which there are two (bifocals), or three (trifocals) distinct portions of different focal power
• Allows the wearer to have two (or three) pairs of spectacles in one
• A trifocal will allow the wearer to have a clear (though small) intermediate portion

Question 19

What are the advantages of bifocals?

Answer 19

1. Convenience – not changing between specs
2. Cheaper than buying two separate pairs of spectacles
3. Less likely to lose specs
4. More convenient for handicapped presbyopes
5. Large and clear reading zone

Question 20

What are the disadvantages of bifocals?

Answer 20

1. Aesthetically not ideal
2. Implicitly associated with age
3. Image jump - Big problem navigating steps/stairs

Question 21

What are progressive addition lenses?

Answer 21

• A lens having optics that vary in power such that the power gradually increases from distance, to the near portions of the lens
• Good for everyday wear

Question 22

What are extended focal lenses?

Answer 22

• A lens that is from the near add power at the bottom of the lens to an intermediate power at the top of the lens
• Designed for desk/computer use

Question 23

What is Interpupillary Distance?

Answer 23

• Distance between the visual axes of the eyes

Question 24

What is angle kappa?

Answer 24

• The angle between the visual axis and the pupillary axis
• Larger in Emmetropes
• Does not vary with gender
• Decreases with increasing age
• Angle kappa ranges from 2-9 degrees (avg: 5.5 degrees)

Question 24

What is angle kappa?

Answer 24

• The angle between the visual axis and the pupillary axis
• Larger in Emmetropes
• Does not vary with gender
• Decreases with increasing age
• Angle kappa ranges from 2-9 degrees (avg: 5.5 degrees)

Question 25

What are the normal values of PD for adult males, females and child under 12

Answer 25

Adult males – 62 to 77 mm

Adult females – 60 to 66 mm

Child < 12 years old – 50 to 59 mm

Question 26

What are the hierarchy of accuracy for PD measurements? List from most accurate to least

Answer 26

1. Visual axis measurement using a pupillometer
2. Visual axis measurement using a PD ruler and a fixation light
3. Pupillary axis measurement using a PD ruler

Question 27

What is a Pupillometer?

Answer 27

• An instrument designed specifically to measure the PD using corneal reflections (based on visual axes)
• Can measure distance, computer, near & monocular PDs

Question 28

What are the near PD measurements rule of thumb?

Answer 28

For 40 cm reading distance, rule of thumb;
- Dist PD < 60 mm, NPD = 2 mm
- Dist PD < 60-70 mm, NPD = 3 mm
- Dist PD > 70 mm, NPD = 4 mm