Optics

Question 1

How is index of refraction calculated?

Answer 1

How much speed of light is alterred as it passes through the material.
n = speed of light in vaccum/speed of light through material

Question 2

What are the 2 types of lenses?

Answer 2

Convex - A converging lens takes light rays and brings them to a point.
Concave - A diverging lens takes light rays and spreads them outward.

Question 3

What is emmetropia?

Answer 3

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

Question 4

What is ametropia and what are the types?

Answer 4

Mismatch between axial length and refractive power. Parallel light rays don’t fall on the retina (no accommodation)
Near-sightedness (Myopia)
Farsightedness (Hyperopia)
Astigmatism
Presbyopia

Question 5

What is myopia and what causes it?

Answer 5

Parallel rays converge at a focal point anterior to the retina. Etiology: not clear, genetic factor
Causes:
excessive long globe (axial myopia) : more common
excessive refractive power (refractive myopia)

Question 6

What are symptoms of myopia?

Answer 6

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

Question 7

What is hyperopia and what are its causes?

Answer 7

Parallel rays converge at a focal point posterior to the retina. Etiology : not clear, inherited
Causes:
excessive short globe (axial hyperopia) : more common
insufficient refractive power (refractive hyperopia)

Question 8

What are symptoms of hyperopia?

Answer 8

Visual acuity at near tends to blur relatively early -
nature of blur varies from inability to read fine print t near vision being clear but suddenly and intermittently blurs.
Blurred vision is more noticeable if person is tired, printing is weak or light inadequate. Asthenopic symptoms.

Question 9

What are asthenopic symptoms?

Answer 9

Asthenopic symptoms: eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis.
BEHB

Question 10

What is an astigmatism and what are its causes?

Answer 10

When parallel rays come to focus in 2 focal lines rather than a single focal point. Etiology : heredity
Cause:
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 11

What are the symptoms of astigmatism?

Answer 11

Asthenopic symptoms (headache , eyepain)
blurred vision
distortion of vision
head tilting and turning

Question 12

What are the treatments of astigmatism?

Answer 12

Regular astigmatism: cylinder lenses with or without spherical lenses (convex or concave), Sx
Irregular astigmatism: rigid cylinder lenses, surgery

Question 13

What is the near response triad?

Answer 13

In humans, near vision is mediated by three separate, but simultaneous pathways.
Pupillary Miosis (Sphincter Pupillae) to increase depth of field
Convergence (medial recti from both eyes) to align both eyes towards a near object
Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision

Question 14

What is presbyopia?

Answer 14

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

Question 15

What treatments are used for presbyopia?

Answer 15

Convex lenses in near vision loss
Reading glasses
Bifocal glasses
Trifocal glasses
Progressive power glasses

Question 16

What are indications and advantages of contact lenses?

Answer 16

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 17

What are disadvantages and potential complications of contact lenses?

Answer 17

Disadvantages: careful daily cleaning and disinfection, expense
Complication : infectious keratitis, giant papillary conjunctivitis, corneal vascularization, severe chronic conjunctivitis

Question 18

What are intraocular lenses?

Answer 18

Replacement of cataract crystalline lens. Give best optical correction for aphakia, avoid significant magnification and distortion caused by spectacle lenses.

Question 19

What are methods of surgical correction?

Answer 19

Keratorefractive surgery:RK, AK, PRK, LASIK, ICR, thermokeratoplasty
Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL

Question 20

Describe the steps of eye surgery

Answer 20

Pre operative eye
Initial cutting of corneal flap
Cutting of corneal flap
Flipping of corneal flap
Photorefractive treatment (laser)
Corneal stroma reshaped post laser
Corneal flap back in position
Treatment completed

Question 21

How does the ICL lens work?

Answer 21

The Staar intra-collamer lens (ICL) is inserted into the eye for the correction of myopia and astigmatism.

Question 22

Describe clear lens extraction and intraocular lens surgery

Answer 22

Same as cataract extraction. Artificial lens implanted. Accomodation lost so reading glasses needed. Phaco tip (ultrasound) used to remove lens.