6

Question 1

Number one complaint of a pt presenting for LV services?

-Most popular LV device?

Answer 1

READING

-Hand magnifier! (HH mag)

Question 2

In order to all 1M reading (standard), what power must be greater than the other?

Answer 2

F LVD > F eq

-LVD’s power must be greater than the equivalent power necessary for the pt to read 1M (20/50) print

Question 3

Three uses for the term “Mag” - X-RATED!!

Answer 3

1) RSM - relative size mag - make object physically larger (i.e. large print books)
2) RDM - relative distance mag - bringing object (or patient closer - both will increase retinal image size
3) Angular mag

Question 4

Formula for relative dist mag?

Answer 4

RDM = orig dist/new obj dist (40cm orig, moved to 20cm = 2X)

Question 5

Effective mag compares the angular sizes of what two things? What’s the formula?

• Assumes the object is also WHERE w/ respect to the HHmagnifier?
• Which LVD brand uses this formula?

Answer 5

Meff = F/4 –> more commonly used

• angular size of image to angular size of object assuming reference distance of 25cm - object must be held @ 25cm from spectacle plane
• Eschenbach

Question 6

What is the magnification of a 4 diopter lens?

Answer 6

1X - because that’s assumed. F/4 = 4/4 =1

Question 7

Conventional mag formula? Why the extra step?

-Which popular company uses the conventional mag formula?

Answer 7

(F/4) + 1

• accounts for accommodation…it just adds one. period.
• Optolec

Question 8

Define: angular mag. Formula?

• which two LVDs is this mainly used with?

- what must be given when angular mag is used with a hand magnifier?**

Answer 8

magnification of the image created completely by the optics of the LVD being used

Angular Mag = 1 + hF; h=dist from mag to spect. plane (m), F=lens power

1) HH mags, 2) telescopes
- the DISTANCE the magnifier is held from the spectacle plane

Question 9

Prism half-eyes are what type of LVD? Advantage? Disadv?
-Prism incorporated is in what direction? Purpose?

-Without any prism, it becomes hard to converge past how many diopters of convergence demand?

Answer 9

• Microscope - large FOV; but NEAR WD (smell the text)
• BI; reduces BO demand (convergence demand) at near

~10D of convergence demand (~10cm away)

-pt learns to move text past the lens, rather than moving head/lens

Question 10

How much BI prism will you Rx in a pair of prism half-eyes with a +4.00 add? +6.00 add? +8.00 add?

• for the above values, is this in EACH eye, or a total??
• Do you take the distance power into account?

Answer 10

+4.00D => 6D BI, EACH eye (so 12D total!)
+6.00D => 8D BI, EACH eye
+8.00D => 10D BI, EACH eye
-note that the near point had NOTHING to do w/ the power of the lens (dist power) - ONLY the near add matters!

-NO - take the ADD POWER ONLY

Question 11

Cardinal rule with hand magnifiers (how does the SIZE of the lens affect the AMOUNT of magnification?)

-where should you hold the object w/ respect to the magnifier?

Answer 11

the LARGER the hand magnifier, the WEAKER it is!

• but you can only see a word or two if it’s super small/strong…
• hold object at ANTERIOR focal point of the magnifier

Question 12

T/F: if the object of interest is at the anterior focal point of the handheld magnifier, it does NOT matter how far you hold the magnifier from your glasses

Answer 12

TRUE - Feq is independent of eye to lens distance! (therefore, F1 = Feq)

Question 13

as the power of the hand magnifier increases, the useable FOV _____

-as the distance of the hand magnifier from the spectacle plane increases, the FOV of the magnifier ____

Answer 13

decreases

descreases

…just think about it ;) makes sense

Question 14

What type of image is ALWAYS created by a stand magnifier?

-IMPORTANT - THE OBJECT AND IMAGE DISTANCES are always (positive/negative)?

Answer 14

virtual, erect, divergent image - ALWAYS!!!
-b/c its divergent - you ALWAYS need an add to see clearly thru it!

-NEGATIVE! -use them to figure out L+F=L’; usually solving for L’

Question 15

What is the relative distance mag of a CCTV when viewed from 40cm?

-What to do when you’re viewing the CCTV from a distance CLOSER than the standard 40cm? (What do you multiple together?)

Answer 15

RDM = 1 @ 40cm (just a standard.)

closer? RDM x RSM = total mag

Question 16

Kindles/E-readers can mag up to _._M print (typically)

iPads can mag up to _._M print

Answer 16

2. 5

3. 2

Question 17

When calculating the near point for a pair of prism half-eyes, what do you use?

Answer 17

the ADD POWER ONLY! Don’t do 1/the whole dist and reading power. ONLY the add.

-recall: the amt of prism is 2prism diopters MORE than the add itself, PER EYE

Question 18

MAX add possible in a pair of:

• PALs:
• FT - bifocals:
• ROUND bifocals:
• Unilens Stick-on microscopic bifocal:

Answer 18

+4.00
+8.00
+24.00
+40.00
-remember: NEAR PD will need to be calculated depending on whether you want prismatic relief! CAN’T just take the near PD!
-NO relief: NPD = DPD -1.5(add); 2.0 if you want relief

Question 19

If you’re using a HH magnifier with the object AT the anterior focal point of the lens, should you use the add or distance portion of the lens?

Answer 19

No need for the add - parallel light leaving! Use distance

Question 20

If a pt is using a 10D HH magnifier and is holding the object at 7cm (inside the focal point of the magnifier), should they use the distance or add portion of their glasses?

Answer 20

ADD REQUIRED - diverging light is leaving the object

Question 21

If the question reads F1 (the LVD) at AT the spectacle plane, what two values do you need to solve the equation?

Answer 21

F1 and F2 - no need for c; because the distance from the magnifier to the spectacle plane is 0.

Question 22

What’s the formula to find the linear field of view for a HH mag?

Answer 22

W = (df)/h ==> ALL UNITS MUST MATCH (put them all in cm)

d=lens dia
f=focal length
h=dist HHmag to EYE

Question 23

A patient is known to have tremors, and also happens to have Glaucoma. What LVD do you suggest? Why?

Answer 23

STAND magnifier - beneficial for tremors, and PERIPHERAL field defects. Also works for RP.

Question 24

Feq for HH mag equation:

Answer 24

Feq = F1+F2 -cF1F2

Question 25

Feq equation for STAND mags: How to find ER?

Answer 25

Feq = ER x add

ER = (L’ - F)/L’

Question 26

Feq equation for CCTVs: How to find Mt?

-RDM X RSM is another way; what’s RDM if working dist = 40cm? 20cm?

Answer 26

Feq = Mt x add

Mt = img linear size/obj linear size

RDM @ 40cm = 1

anything closer than 40cm: RDM X RSM to figure it out (if 20cm working dist, then RDM = 2x, and it’ll tell you what RSM is)