Visual System Optics

Question 1

What happens in refraction?

Answer 1

As light goes from one medium to another, the velocity changes

Question 2

Do all substances have an index of refraction?

Answer 2

Yes

Question 3

How do you figure out index of refraction?

Answer 3

speed of light in vacuum / speed of light in medium (must be less than 1 or equal to)

Question 4

What happens as light goes from one medium into another?

Answer 4

the path changes, some of light reflects of the boundary and some light refracts through the boundary

Question 5

What is the angle of incidence equal to?

Answer 5

angle of reflection

Question 6

What changes depending on direction fo light?

Answer 6

Angle of Incidence > or < the Angle of refraction depending on the direction of the light

Question 7

What are the two types of lenses?

Answer 7

1. Convex

2. Concave

Question 8

What is a convex lens?

Answer 8

Converging lens (convex) takes light rays and brings them to a point

Question 9

What is a concave lens?

Answer 9

A diverging lens (concave) takes light rays and spreads them outward

Question 10

What is an application of a converging lens?

Answer 10

A camera uses a lens to focus an image on photographic film

Question 11

What happens in emmetropia?

Answer 11

• Adequate correlation between axial length and refractive power
• Parallel light rays fall on the retina (no accommodation)
• perfect eye

Question 12

What is ametropia (refractive error)?

Answer 12

• Mismatch between axial length and refractive power

- Parallel light rays don’t fall on the retina (no accommodation)

Question 13

What are types of ametropia?

Answer 13

1. Near-sightedness (Myopia)
2. Farsightedness (Hyperopia)
3. Astigmatism
4. Presbyopia

Question 14

What is myopia? What are the different types?

Answer 14

• Parallel rays converge at a focal point anterior to the retina
• Etiology : not clear , genetic factor

Question 15

What are the symptoms of myopia?

Answer 15

1. Blurred distance vision
2. Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
3. Headache

Question 16

What is hyperopia?

Answer 16

-Parallel rays converge at a focal point posterior to the retina
Etiology : not clear, inherited

Question 17

What are the symptoms of hyperopia?

Answer 17

1. visual acuity at near tends to blur relatively early
2. asthenopic symptoms
   - eyepain
   - headache in frontal region
   - burning sensation in the eyes
   - blepharoconjunctivitis
3. Amblyopia – uncorrected hyperopia > 5D

Question 18

What is the blurriness like in hyperopia?

Answer 18

1. nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently blur
2. blurred vision is more noticeable if person is tired , printing is weak or light inadequate

Question 19

What is astigmatism?

Answer 19

Parallel rays come to focus in 2 focal lines rather than a single focal point

Question 20

Where does astigmatism come from?

Answer 20

Hereditary

Question 21

What is the cause of astigmatism?

Answer 21

refractive media is not spherical–>refract differently along one meridian than along meridian perpendicular to it–>2 focal points (punctiform object is represent as 2 sharply defined lines)

Question 22

What is happening in astigmatism?

Answer 22

• The two meridians (I and II) are perpendicular to each other
• A punctiform object (o) is represented as a line segment Y0 And Y1 at the focal points of the two meridians
• Midway between these two focal points is the “circle of least confusion” (Kr), the location with the least loss of image definition

Question 23

What are the symptoms of astigmatism?

Answer 23

1. Asthenopic symptoms (headache , eyepain)
2. blurred vision
3. distortion of vision
4. head tilting and turning

Question 24

What is the treatment of regular astigmatism?

Answer 24

cylinder lenses with or without spherical lenses (convex or concave), Sx

Question 25

What is the treatment of regular astigmatism?

Answer 25

igid cylinder lenses, surgery

Question 26

What is the near response trio?

Answer 26

1. Pupillary Miosis (Sphincter Pupillae) to increase depth of field 2. Convergence (medial recti from both eyes) to align both eyes towards a near object 3. Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision

Question 27

What is presbyopia? How is it treated?

Answer 27

1. Naturally occurring loss of accommodation (focus for near objects) 2. Onset from age 40 years 3. Distant vision intact 4. Corrected by reading glasses (convex lenses) to increase refractive power of the eye

Question 28

What is the treatment of presbyopia?

Answer 28

* convex lenses in near vision * Reading glasses * Bifocal glasses * Trifocal glasses * Progressive power glasses

Question 29

What are different types of spectacle lenses of presbyopia correction?

Answer 29

1. Monofocal lenses : spherical lenses , cylindrical lenses | 2. Multifocal lenses

Question 30

What are contact lens in presbyopia correction?

Answer 30

-higher quality of optical image and less influence on the size of retinal image than spectacle lenses indication -cosmetic , athletic activities , occupational , irregular corneal astigmatism , high anisometropia , corneal disease

Question 31

What are the disadvantages of contact lenses?

Answer 31

1. careful daily cleaning 2. disinfection 3. expense

Question 32

What are the complications of contact lenses?

Answer 32

1. infectious keratitis 2. giant papillary conjunctivitis 3, corneal vascularization 4. severe chronic conjunctivitis

Question 33

What are intraocular lenses?

Answer 33

* replacement of cataract crystalline lens | * give best optical correction for aphakia , avoid significant magnification and distortion caused by spectacle lenses

Question 34

What is Keratorefractive surgery

Answer 34

RK, AK, PRK, LASIK, ICR, thermokeratoplasty

Question 35

What is intraocular surgery?

Answer 35

clear lens extraction (with or without IOL), phakic IOL

Question 36

What is the process of surgical correction?

Answer 36

1. Pre operative eye 2. Initial cutting of corneal flap 3. Cutting of corneal flap 4. Flipping of corneal flap 5. Photorefractive treatment (laser) 6. Corneal stroma reshaped post laser 7. Corneal flap back in position 8. Treatment completed

Question 37

When is Staar intra-collamer lens (ICL) inserted?

Answer 37

for the correction of myopia and astigmatism, lens on top of normal lens, but sooner or later the natural lens becomes more opaque so will have to remove both lenses before cataract operation

Question 38

What is clear lens extraction and intraocular lens?

Answer 38

- IOL: Intra ocular lens. - Same as cataract extraction - Implantation of artificial lens - Lose accommodation (patient will need reading glasses) - Lens softer, coo expectation higher than regular cataract surgery

Question 39

What are the causes of myopia?

Answer 39

* excessive long globe (axial myopia) : more common | * excessive refractive power (refractive myopia)

Question 40

What is the treatment of myopia?

Answer 40

1. Correction with diverging lenses (negative lenses) 2. Correction with contact lens 3. Correction by removing the lens to reduce refractive power of eye

Question 41

What are the causes of hyperopia?

Answer 41

•excessive short globe (axial hyperopia) : more common •insufficient refractive power (refractive hyperopia) -With high hyperopia, hard to see objects near, and myopia always be always be able to see near and read so important in children

Question 42

What is the treatment with hyperopia?

Answer 42

1. Correction with converging (positive lenses) 2. Correction with positive lens + cataract extraction 3. Correction with contact lens 4. Correction with intraocular lens

Question 43

How is pupil constriction mediated in near response triad?

Answer 43

contraction of the circular Sphincter Pupillae Muscle within the Iris

Question 44

Why is a larger depth of field better in near response triad?

Answer 44

-the eye optical system is able to maintain clear focus over a certain range of viewing distances, even without relying on accommodation -Eyes with shallow depth of field loose focus easily, even with the slightest object movement, when viewing a near object

Question 45

What happens in convergence in the near response triad?

Answer 45

both eyes adduct medially at the same time, | to align both eyes towards a near object

Question 46

How is convergence in the near response triad mediated?

Answer 46

mediated by the simultaneous contraction of medial rectus extra-ocular muscles from both eyes

Question 47

Why is accommodation important in the near response triad?

Answer 47

the lens accommodates, | thus increasing the refractive power required to focus on a near object

Question 48

What happens to our lens over time?

Answer 48

natural lens looses its elasticity

Question 49

What is the problem with intraocular lenses?

Answer 49

monofocal lenses, so patient loses possibility to accommodate so help long distance but reading need help/spectacles

Question 50

What is in a cataract surgery?

Answer 50

1. Remove natural lens by ultrasound tip which breaks and sucks up natural lens 2. Then place artificial lens same position as natural lens