9 - Telescopes, Telemicroscopes

Question 1

Random rogue memorization: height of a 20/20 letter at 20ft

Answer 1

8.87 mm

Question 2

Telescopes

• in LV, __ is always __
• Galilean
• Keplarian

Answer 2

Objective = plus

G: aka terrestrial, minus ocular

K: aka astronomicals, plus ocular

Question 3

Galiliean telescopes

• lens separation equation
• afocal telescopes

Answer 3

d = (1/F1) + (1/F2)

Afocal = vergence amplifiers

Question 4

YAY MATH!
1) what type of scope, what is the separation bw the lenses:
F1 = +5D
F2 = +20D

2) what type of scope, what is the separation bw the lenses:
F1 = +5D
F2 = -20D

Answer 4

1) keplarian (both plus)
d = (1/5) + (1/20) = 25cm

2) galilean (minus, plus)
d = (1/5) + (1/(-20)) = 15cm

Question 5

Magnification by telescopes

• angular magnification equation
• Galilean vs Keplarian

Answer 5

M = -F(ocular)/F(objective)

G: M is positive (minuses cancel)

K: M is negative - image is inverted, needs mirrors to upright it

Question 6

Exit pupil

• Galilean vs Keplarian
• the closer the exit pupil to the eye’s pupil…

Answer 6

G: inside scope
K: outside scope

The larger the FOV

Question 7

Telescopes of equal power
-Galilean vs Keplarian
—length
—FOV
—cost

Answer 7

G: shorter length, smaller FOV, cheaper

K: longer length, larger FOV, expensive

Question 8

RXing telescopes

• what equation do you use
• if pt has no specific goal, use what

Answer 8

M = got/need

20/40

Question 9

YAY MATH!

Pt reads 10/60. They want to view the board at 20ft and need 20/40 to do so. What strength telescope do you want to try

Answer 9

3x

10/60 = 20/120

Got/need = 120/40 = 3x

Question 10

Telescopes: practical limits

• what are they
• what occurs beyond these limits

Answer 10

2x-8x

Extremely limited FOV, difficult to maintain steady image

Question 11

Demonstration of telescopes

• begin with
• what to try if they struggle with beginner
• what to try if successful

Answer 11

Galilean 2.5x

Binoculars, empty paper towel roll

Low power Keplarian -> predicted scope

Question 12

Telescopes

-what does 4x12 mean on a hand-held

Answer 12

4x magnification

12 = objective diameter

Question 13

Low power scopes

-more likely to be what type

Answer 13

Galilean

Question 14

Scope example

-the Eschenbach is a glasses-type magnification device without mirrors. What type of scope is it

Answer 14

Galilean - K requires mirror for upright image

Question 15

Implantable mini telescope (CentraSight)

• when it’s implanted
• only approved for whom
• what do you lose in that eye

Answer 15

Cataract surgery

End-stage AMD

Peripheral vision

Question 16

Near-focused scopes

-how they focus at near (2)

Answer 16

Adding a plus lens in front of objective = parallel light rays enter scope

Change tube length

Question 17

Magnification by a telemicroscope

-equations

Answer 17

M(cap) = rF(cap)

Question 18

YAY MATH!
Telemicroscope problem: predict what letter size a pt should be able to see given:
Near acuity with +2.00 add is 0.5m/4M
Uses 2x telescope with 5D cap

Answer 18

0.8M (slide 49)

Question 19

Telemicroscope vs microscope

• FOV
• WD

Answer 19

TMS = small FOV, large WD

MS = large FOV, small WD

Question 20

Equivalent power

-equation

Answer 20

Fe = F(cap) * M(TS)