3) Monocular Subjective Refraction

What is the purpose of monocular subjective refraction?

→ determine pt’s refractive status using the pt’s input

• subjective test

  • not fully subjective b/c the clinician’s subjectivity is taken into account too (DR judges the PT’s responses)

What is the goal of monocular subjective refraction?

→ improve pt’s vision to best corrected

• this may not always be 20/20

• if you can’t get your pt to 20/20, 2er cause of ↓VA MUST be explained!

List circumstances that make achieving 20/20 best-corrected vision more difficult.

• Retinal disease

• Media opacity

• Amblyopia (refractive / strabismic)

• Neurological issues

What is the key principle underlying successful refraction?

→ Establishing effective communication during the process

• Pt needs clear understanding of what is expected of them

• Examiner needs clear understanding of pt’s responses

What is the examiner’s role in determining the final rx during refraction?

→ Merge objective (retinoscopy) with subjective (pt’s visual complaints, daily visual demands, habitual rx, VA measurements) findings to create final rx

• Objective + Subjective = Final RX

Give examples of patients who may not be good candidates for manifest refraction (“What’s better 1 or 2”?)

• Non-verbal pt

• Intellectual disabilities

• Very young children

• Malingering pt

  • may fabricate or exaggerate symptoms (e..g, want glasses)

    • seen in young children esp girls

STEP 1)

What does refractive analysis begin with? What are things you can do as a clinician during this stage?

Patient History!

• Identifies pt’s perceived visual difficulty

• VA ≠ patient satisfaction

  • 20/25 may feel poor vision, BUT a 20/40 may feel comfortable

As a clinician:

• Listen carefully to pt concerns

• Educate patient on expected visual changes over time

  • young myopes - vision worsens, then stabilizes at ~25 yrs old

  • hyperopes - will need readers in a few years

What are typical behaviours shown by myopes?

• Blurred distance vision (esp in dim illuminations)

• Holding objects closer/moving closer to see

• Needing to squint to see

What are typical behaviours shown by hyperopes?

• Adults = trouble reading

  • Large hyperopes or older adults = blurred distance vision (bc lens can’t pull image front onto the macula)

• Young adults = intermittent blur when fatigued or in poor lighting (bc lens can still pull image front onto the macula, but pt experience eyestrain)

  • headaches with near work (worsens as day progresses)

  • possible diplopia at near

• Children/teens = no visual complaints, but may avoid near work

Note: These symptoms vary greatly by age & magnitude of error

What signs do both myopes of hyperopes exhibit when they require more power?

Myopes = push glasses back towards face

Hyperopes = push glasses down to nose

What are typical behaviours shown by astigmats?

• Vision complaints at distance AND near

  • May be worse at one or the other

• Head tilting with oblique axis

• Squinting

• Ghosting or doubling of images

  • ghosting = shadow appears behind obj

• ↓ astigmats usually have good vision

  • may experience tired eyes when doing detail oriented work

• ↑ astigmats = ↓ acuity (even if they dont have myopia or hyperopia)

STEP 2)

After patient history, what does a clinician assess?

VA – both distance & near using pt’s best corrected acuity

• ↓ vision at distance OR near = RE is likely the culprit (✅)

• ↓ vision at distance AND near = RE is possibly the culprit (⚠)

Rule of thumb for Estimation of RE: Myopia (simple vs compound)

Simple myope: each line of decreased acuity = -0.25D

Compound myope: each line of decreased acuity = -0.25D SE

• SE = sph power + ½ cyl power

Rule of thumb for Estimation of RE: Hyperopia

Hard to estimate based on VA

• Young patients - with active accommodation may have good distance VA with large RE (20/20 distance vision with +3.00D hyperope)

• Presbyopes - ↓ distance & near vision

  • can estimate +0.25-0.50D increased power per line of decreased vision

  • so presbyope’s new rx can be estimated like myopes (but their change is not linear like myopes)

Rule of thumb for Estimation of RE: Astigmatism

→ Estimation includes amount & orientation of astigmatism

• ↓ impact on VA = ↓ astig amounts

• ↑ impact on VA: oblique > ATR > WTR (WTR has least impact on VA) (orientation)

STEP 3)

After VA, what does a clinician assess?

Lensometry!

1. pt’s current rx

2. whether or not pt is wearing their glasses correctly

Define Lens effectivity.

Change in vergence of light occurring at different points along the path

What does Effective lens power depend on?

location in front of the eye

What happens to lens power when a lens is moved closer or farther from the eye?

💡 Connects to the “behaviour” myopes and hyperopes show when they need more power

STEP 4)

Once you have results of history, acuity & lensometry, what should you be able to do?

→ generate a “hypothesis” of what you expect pt’s RE to be

• check if VA matches the pt’s symptoms

• identify what type of RE explains the complaint

• decide what Rx change should improve vision if VA is reduced

• evaluate the reliability of patient responses

  • prevents the pt from controlling the exam

Scenario #1: What is the diagnosis under each VA?

Patient Complaint: I feel like I can’t see well when I drive home at night

• Visual acuity #1: 20/30 distance, 20/20 near

• Visual acuity #2: 20/30 distance, 20/30 near

Based on:

Patient’s complain = Myopia, hyperopia, astigmatism

• Visual acuity #1 = Myopia (since pt can see 20/20 at near)

• Visual acuity #2 = Hyperopia or astigmatism

Scenario #2: What is the diagnosis under each VA?

Patient Complaint: My eyes feel tired after working on the computer all day

• Visual acuity #1: 20/20 distance, 20/30 near

• Visual acuity #2: 20/30 distance, 20/25 near

Based on:

Patient’s complain = Hyperopia, astigmatism (myopes can’t sense computer strain, unless its uncorrected)

• Visual acuity #1 = Hyperopia (b/c distance is 20/20)

• Visual acuity #2 = Astigmatism

What is Just Noticeable Difference (JND) (aka “which is clearer 1 or 2?”)?

→ amount of optical change required for a difference in clarity or blur to be noticed

How to estimate JND?

1. Divide Snellen acuity denominator by 100 = JND

2. For a pt to show a difference of ___D JND a cross cylinder lens with + / - (JND/2) is needed

→ e.g., 20/200 = 2.00 JND (cross cylinder lens with +/- 1.00D is needed to show a patient a difference of 2.00D)

• “To show a patient a 2.00-diopter difference, you need a cross-cylinder lens that flips between +1.00 and −1.00.”

What minimum VA is required to perform refraction with a phoropter?

20/50 - if the pt does NOT meet this, refraction should be performed using a trial frame instead

What is the typical JCC lens power built into a phoropter?

0.25 D or 0.50 D

List the 4 main steps of Refractive Determination.

1. Gross Sph Power Determination

2. Cyl Axis Refinement

3. Cyl Power Refinement

   • Cyl Power Search – only done if no cyl was found during retinoscopy

4. Sphere Power Refinement

Why do patients often report that more minus power looks clearer, and what problem can this cause?

→ More (-) power makes the image darker and smaller, which can seem clearer

• this stimulates accommodation

• can lead to near vision difficulty or headaches

What is the goal of refraction when determining final lens power?

→ achieve best visual acuity with the most (+) / least (-) power

• BVA may not be 20/20

What is the JCC and how is it used in cylinder axis refinement?

→ has 2 equal-power cyl with opposite signs to refine cyl axis & power

• cyl are oriented 90° apart

  • Red dots = MINUS cylinder

  • White dots = PLUS cylinder

• SE of the JCC = 0

During “Cyl axis refinement” why do we use 5° and 1°, not 15° and 5° for people who had a retinoscopy cyl of -2.00>?

High astigmatism powers can sense/are sensitive to small axis changes

What is the goal of the “Cylinder Power Refinement” step?

→ Maintaining SE (sph equivalent) to move CLC closer to the retina on either side

• If just change cyl power, you move the CLC off the retina & the focal point of the astig power onto the retina

During the “Cylinder Power Search” what does it mean if the patient said yes to any of axis with the Red dot?

It means you missed finding cylinder on retinoscopy

During the “Cylinder Power Search” what does it mean if the patient said yes to ALL the axis with the White dot?

No cylinder found → pt is a true sph

What do you do if you had a large increase in cyl power during “Cylinder power refinement” (~0.75D or more)?

→ Go back and recheck cyl AXIS at higher power

• pt should be more discriminating due to more appropriate correction – need to make sure it is the correct axis

• If you start with a high cyl power & it decreases – don’t need to recheck axis (b/c we want a low cyl)