Calculating NETs

[LimbalGlow16]

---

Members don't see this ad.

Hey guys so I'm having a hard time understanding how to calculate NET values for PRA, NRA, FCC or cross cylinder, Accommodative Amplitude, high neutral/Mem? What equations do you guys use?

Case 1:
7a or BSBVA: +2.50D
FCC: +1.50D
NRA: + 4.50
PRA: -1.25
AA: - 6.00

Case 2:
7a: -1.75
FCC: -2.50
NRA:0.75
PRA: -2.25
Accom. Amplitude (AA): -5.50

Pretty much once I understand the equations I'll feel better.

Please help!!!
Thxs. 😉

 

[20DOC20]

What kind of cross-cylinder is FCC?

 

[20DOC20]

For your net's, think of it as a number line, with the 7A as your zero point. The point of Nets is to know if the patient is balanced on either side of the 7A at near.

My Formula for Nets= 7A - P or NRA

+2.50 (-) +4.50 = -2.00 for your NET NRA.
+2.50 (-) -1.25 = +3.25 for your NET PRA.
To be honest, I can't remember if you express the NETS with a + or -, because really, that's superfluous if you know it's NET PRA or NET NRA.

OR visualize it:

PRA -1.25 <-------net-------> (+2.50) "7A is Zero" on number line <--net---->NRA +4.50

Example one patient is imbalanced. Net PRA > than Net NRA.

NRA is to the right because it's focusing behind the object and PRA to the left because it's focusing more in front of the object. Think of it as an invisible number line floating in space. Also when expressing the NRA and PRA it's always tested at 14 inches. I ignore the accommodative demand when doing this stuff because it's easy to over think it and get confused.

I like to just visualize it, with 7A as "zero" and count in my head relative to that point the nets. You can also record the gross values and then calculate the nets as needed.

Of course, always check with your optometry school teacher before listening to any math problems calculated by 20DOC20. HA!