Refractions coming out +.50 too strong??

[BMH]

I decided to put this in a new thread but I am curious as to how this might relate to the thread regarding red/green testing.

The situation is this:

My Doc runs four refraction lanes with multiple techs helping him. We don't have a huge Rx check problem but when we do its usually the same problem, the patient is being over-plus about half diopter. The patient's complaint always revolves around poor distance vision.

The doc used to check refraction and send the pt back to the optical with some phantom eyeglass measurement issue (change seg ht or PD 1mm) but of course the Rx would also have less plus power. After many years with him, We finally agreed not to blame the glasses if its the Rx. I always carefully check for eyeglass related issues before taking up his chair time on Rx checks.

Okay here are my questions.
What would make a patient like more plus in an exam room but not in the real world?

He uses flat panel LCD snellen charts, he swares they are calibrated but how could I check them?

He also does not do any duochrome testing. Would that potentially catch this issue?

Your turn...

[Howard Gorin]

Are all lanes the same length?
Do the images on the flat screen measure the same size?
Flat screens are relatively new, did you use projectors before or is this a new installation?

[LENNY]

Are all lanes the same length?
Do the images on the flat screen measure the same size?
Flat screens are relatively new, did you use projectors before or is this a new installation?

How would it relate to the overplus.....?

[wmcdonald]

I decided to put this in a new thread but I am curious as to how this might relate to the thread regarding red/green testing.

The situation is this:

My Doc runs four refraction lanes with multiple techs helping him. We don't have a huge Rx check problem but when we do its usually the same problem, the patient is being over-plus about half diopter. The patient's complaint always revolves around poor distance vision.

The doc used to check refraction and send the pt back to the optical with some phantom eyeglass measurement issue (change seg ht or PD 1mm) but of course the Rx would also have less plus power. After many years with him, We finally agreed not to blame the glasses if its the Rx. I always carefully check for eyeglass related issues before taking up his chair time on Rx checks.

Okay here are my questions.
What would make a patient like more plus in an exam room but not in the real world?

He uses flat panel LCD snellen charts, he swares they are calibrated but how could I check them?

He also does not do any duochrome testing. Would that potentially catch this issue?

Your turn...

Excessive plus will cause a blur at distance every time. It sounds as though there is some issue with the calculation of the system. But, if not happening on every patient then it is not the system. Doing both a monocular and binocular balance helps not to over-plus, or over-minus. Good luck solving the problem.

[obxeyeguy]

Okay here are my questions.
What would make a patient like more plus in an exam room but not in the real world?

I would answer reality. If they take a +.50 in that perfect "little world, 20 feet by mirrors, perfect lighting, perfect little 22mm lens", give them a +.25 for the real world. If you want great refractions for hyperopes, trial frame them and let them walk outside, and even that's a stretch, but better.

[Comma]

If you want to check, just for fun.

Optotype heigh (mm) =

1.454 x d (meters between patient and the chart)
--------------------------------------------
AV (meters or feet, that's the same)


Exemple : h (mm) =

1.454 x 6
---------------------
20/20 (=1) or 6/6 (=1)


Answer : 8.724 mm


Exemple : h (mm)

1.454 x 6
-------------------
20/40 (=1/2) or 6/12 (=1/2)

Answer : 17.448 mm (1.454 x 6 x 2)

[LandLord]

Most likely sounds like inexperience if its being done by a newer tech. Most people could still see 20/20 with an extra +0.25 or +0.50 with no va improvement possible in the exam chair. Outside the lane, a myope will hate the extra plus. Checking the old glasses will usually prevent this problem.

[harry888]

I have a 15 foot exam room with no mirrors where I always need to cut plus by 0.25 (or add 0.25 minus). Remakes were expensive until I figured it out.

My other room is 22 feet. No problems.

I've had 15 foot rooms in the past without having to adjust the Rx.

Some rooms just have a personality all their own.

Harry

[Oedema]

Are the LCD panels on the wall directly in front of the patient, or behind with a mirror? Whats the length of the room?

[Oedema]

Excessive plus will cause a blur at distance every time. It sounds as though there is some issue with the calculation of the system. But, if not happening on every patient then it is not the system. Doing both a monocular and binocular balance helps not to over-plus, or over-minus. Good luck solving the problem.

Actually a binocular balance or duochrome balance will generate take minus power away during the refraction - one must be careful b/c most people really like there minus and if you do a technically correct balance you'll likely to over plus the patient.

[FVCCHRIS]

Get a flipper with -.25 one side, -.50 on the other. I doubt you'll ever solve the actual problem, seeing as how it is being looked into by you and not the Dr.(he doesn't seem to think he has a problem) You can certainly eliminate the chair time for the Rx checks by doing them yourself.

[YrahG]

Get a flipper with -.25 one side, -.50 on the other. I doubt you'll ever solve the actual problem, seeing as how it is being looked into by you and not the Dr.(he doesn't seem to think he has a problem) You can certainly eliminate the chair time for the Rx checks by doing them yourself.

Do you mena -0.25 / +0.25 or -0.50 / +0.50 flippers.

The formula for finding your optotypes heigh is:

tan(5/60) = x / 6000; that would give you the types height in mm or 8.73mm for a 20 foot room. If the patient to chart distance is less than 20ft you'll have issues and it won't be consistent enough between patients to just knock off a certain amount of a prescription, use mirrors to make the distance longer over 20ft if possible.

[Barry Santini]

Keep in mind the dispenser's using "flippers" can be like a child playing with matches...

You have to know what you're doing... (Not saying you don't)

Monocular balance issues MUST be duochromed.

Incomplete/inappropriate astigmatism correction is often evidenced when using the flippers from a patient response that "neither choice looks good/great.

Keep this in mind: Second guessing the Rx you've been given is NOT for the untrained/inexperienced/beginner. Unfortunately, there are no courses in this regard.

Perhaps Dr. Katz of Suffolk, KLI NY will step in and fill the void.

FWIW

Barry

[drk]

You guys are nibbling around the edges.

Here's the answer as was alluded to by Dr. Harry888 and YrahG: the room is too short.

I'm suprised Barry didn't go ballistic on this.

13ft will induce +0.25, and that's what the room will measure. (The other +0.25 is likely phantom.)

It cracks me up to see ODs not understand this. It has nothing to do with the chart, per se.

Think about retinoscopy: Do you leave the lenses in place when you neutralize the mires? No, you subtract the working distance.

Think about near point refraction: If you make the near chart clear, is that the distance Rx? No, you get the lens power to see 40cm clearly.

Think about refracting to a screen 3 meters away: Do you get the distance powers? No, you get the powers to see 3 meters away.

Think about refracting to a screen 13 ft away (4 meters): Do you get the distance power? No, you get the power to see 4 meters away.

Aaahhhh....that's why we need to refract with a chart 6 meters away!

Homework assignment for the OP: measure the back of the exam chair to the front of the screen, and post the distance.

[Barry Santini]

Thanks, drk...I needed that!

Barry

[BMH]

Thanks for all the responses! I'll answer some of the question to night when I'm not at work. I'll also measure the exam rooms and chair placements. Yes the rooms are short.

One quick answer to a question is: The LCD charts are mounted on an opposite wall with a mirror reflecting the chart.

[sharpstick777]

drk nailed it... good post.

There are mirror systems that will increase the perceived distance so that all the rooms can be equalized.

[sharpstick777]

BMH,
I worked in a large practice with 6 MDs and the opticians were given terrible refractions. Over all we had over a 22% Drs. Rx change redo rate. With so many MD's and even more techs it was impossible to trace the bad refractions back.

It was a hassle, but i started going through the charts looking for changes and dicrepancies. Did the axis change 90 degress between the Autorefractor and the subjective refraction? was there a huge change between the old rx and new? worse, some of the Drs were thinking in plus cyl but writing in minus (we were all supposed to use minus).

Anyone with any strangeness (excluding post op cataracts patients) I began trial framing them. Made the techs mad, but the patients were happy, we cut redos by 2/3 rds. Although it was a lot of time, it eventually saved time because redo's were a nightmare.

[Barry Santini]

drk nailed it... good post.

There are mirror systems that will increase the perceived distance so that all the rooms can be equalized.

Be careful, however, when using mirrors to fold the test length. Studies have shown that patients are often focus- influenced by the proximity of the "mirrored" wall, and any items (pictures, diplomas, etc.) you may have mounted on it. Also, the "frame" around the mirror (or even the unframed border of a mirror) at 10 feet will induce unwanted accomodation.

I see this all the time in my own CL lane.

FWIW

Barry

[john-atlanta]

I was having a big problem with overplussing patients when I went out on my own and opened my own office. I installed an LCD system, direct view and calibrated the size.

After much frustration, trying to adjust for the working distance etc. Finally, I gave up and had the electrician move the monitors to the back wall, installed mirrors and recalibrated (plus changed the software to mirror view) and the problem was essentially eliminated. Now I am seeing patients a year later, and even when they did not complain or come back, sure enough a bunch of them were overplussed.

So, while the mirror is not a perfect solution, it certainly has helped a lot. I chose a frame that is almost the same color as the wall and the wall with the mirror has no art on it.

John

[john-atlanta]

Also, is the patient being refracted after dilation? That can be a common cause of overplussing.

[YrahG]

You guys are nibbling around the edges.

Here's the answer as was alluded to by Dr. Harry888 and YrahG: the room is too short.

I'm suprised Barry didn't go ballistic on this.

13ft will induce +0.25, and that's what the room will measure. (The other +0.25 is likely phantom.)

It cracks me up to see ODs not understand this. It has nothing to do with the chart, per se.

Think about retinoscopy: Do you leave the lenses in place when you neutralize the mires? No, you subtract the working distance.

Think about near point refraction: If you make the near chart clear, is that the distance Rx? No, you get the lens power to see 40cm clearly.

Think about refracting to a screen 3 meters away: Do you get the distance powers? No, you get the powers to see 3 meters away.

Think about refracting to a screen 13 ft away (4 meters): Do you get the distance power? No, you get the power to see 4 meters away.

Aaahhhh....that's why we need to refract with a chart 6 meters away!

Homework assignment for the OP: measure the back of the exam chair to the front of the screen, and post the distance.

Thank you DrK, it is nice having a doctor of your caliber confirm my suspicions. :cheers:

[Barry Santini]

Also, is the patient being refracted after dilation? That can be a common cause of overplussing.

Yes, because of corneal SA (spherical aberration).

Barry

[flexonman]

Our problem turned out to occur in our lanes that were less than 20 feet. We used 6/6. To verify we took the patient out of the lane and used our hallway. This solved the problem.

[Robert Martellaro]

(The other +0.25 is likely phantom.)

You're already +.17 at 6 meters, so I suspect that the Mds round up on plus and down for minus, where the ODs go the opposite direction, probably because of the age of their respective clients.