Phorometry (Distance)

What is the relationship between prisms & lens with accommodation?

• Relaxes Accommodation:

  • plus lenses relax accommodation (duh, older people need cheaters bs can’t accommodate)

  • BI prism diverges the eyes (duh, apex is pointing out)

• Stimulates Accommodation:

  • negative lenses stimulate accommodation (why it’s important not to over minus the patient)

  • BO prism converges the eyes (duh, apex is pointing in)

What is the purpose of accommodation & vergence?

• accommodation is for CLEAR vision

• vergence is for SINGLE vision

When should you not perform phorometry?

monocular patients (like strabismus patients or amblyopic patients)

Note: Since it is not for strabismus patients, then if there is a question regarding movement on UCT then this would not be an appropriate test to perform.

Distance phorometry testing order?

1. Horizontal phoria

2. Vertical phoria

3. Horizontal vergence amplitudes (BI then BO)

4. Vertical vergence amplitudes (only if vertical phoria is present)

Horizontal phoria procedure at distance?

• 6 BD OD & 12 BI OS

• An isolated letter 1-2 lines above the patients BVA in the poorer seeing eye

• “You should see two images: one up to the right & one down to the left. I’m going to be covering the lower image & moving it. As soon as I show it to you again, tell me where it is: still to the left, to the right, or just beneath the top letter. Our goal is to line up the two letters like buttons on a shirt.”

• Flash the left eye (do not let them view the targets binocularly for an extended period of time)

• Change prism by 3 to 4 pd at a time

• endpoint is when the images are lined up like buttons on a shirt!

Documenting:

• 3pd BI = 3pd XP

• 3 pd BO = 3pd EP

Vertical phoria procedure at distance?

• 6 BD OD & 12 + results from horizontal phoria BI OS

• Check the alignment of the phoropter & that the patient is not tilting there head!

• An isolated letter 1-2 lines above the patients BVA in the poorer seeing eye

• “You should see two images: one up to the right & one down to the left. I’m going to be moving the upper image. As soon as I show it to you again, tell me when the two line up side-by-side like headlights on a car.”

• Do NOT flash the target!

• Change prism slowly

• endpoint is when the images are side-by-side like headlights on a car!

Documenting:

• 3pd BU = RHoP

• 3pd BD = RHrP

What’re the concerned vergence ranges of an EP vs. an XP? HypoP vs. Hyper

• EXOphoria: Positive fusional vergence (CONvergence) = BO ranges

• ESOphoria: Negative fusional vergence (DIvergence) = BI ranges

• HyperP: Infravergences = BU

• HypoP: Supravergences = BD

Horizontal vergence amplitudes at distance procedure?

• 0 prism to start on both eyes

• Vertical column of 20/50 to 20/20 letters

• BI ranges first THEN BO ranges

• When moving the prism, make sure to do it slow & simultaneously!

• “I want you to concentrate on keeping the letters as clear as you can and tell me when they first look a little blur or when they first break into two.”… “Now tell me when they go back into one.”

• When documenting blur/break/recovery you must add the prisms in both eyes for your final answer!

Note: The pt should not see blur during this procedure. If the pt see’s blur then they’re over minused!

Documenting:

• X / 10 / 4

• 5 / 10 / 4 (over minused!)

Vertical vergence amplitudes at distance procedure?

• 0 prism of right eye (no prism over left eye)

• Horizontal line of letters 1-2 lines BVA of the patients poorer seeing eye

• Only perform this test if the patient has a vertical phoria

• Make sure to move the prism slowly

• “I want you to concentrate on looking at the line of letters and keeping it clear. Tell me as soon as the letters first start to double.” DO NOT ASK FOR BLUR! … “Now tell me when the letters first go back into one”

• When documenting, there is no need to add the prisms from both eyes BUT you must put whether you’re testing supravergence or infravergence (as well as base direction)!

Documenting:

• Right supravergence: 3pd BD/1pd BD (X / 3 / 1)

• Left infravergence: 5pd BU/2pd BU (X / 5 / 1)

Which phorometry test can confirm a vertical phoria?

Vertical vergence ranges! Specifically, asymmetrical supra & infra vergences may confirm a vertical phoria!

Example:

• Right supravergence: 3pd BD/1pd BD

• Left infravergence: 5pd BU/2pd BU

• 3pd BD - 5pd BU = 2pd BU

• 2 pd BU / 2 = 1pd BU OD

• This is interpreted as 1pd RHypoP

Note: The ranges are from the same eye (can’t compare right supra vergences with left supra vergences)! Also, the BREAK of the patient is what’s used to determine the phoria NOT the recovery!

When should there NOT be blur in distance phorometry testing?

• Distance BI ranges during horizontal vergence amplitudes! (This means the patient is over minused)

• Vertical vergence amplitudes (never blur with vertical accommodation test because our brains can’t accommodate vertically)