Subjective and Objective Refraction

Subjective Refraction

examiner communicates with the patient and determines the optical correction that best suits the patient

Subjective Refraction

it is only possible to perform SR/MR with patients who can communicate effectively

Objective refraction

only when SR/MR is not possible, limited or unreliable not based on patient's judgment

Objective refraction

it is preferable to have more than one assessment (retinoscopy and autorefraction)

Subjective Refraction

Should be performed under conditions that simulate the patient's normal viewing situation as closely as possible

room

Normally, in subjective refraction, this would be the pupil size under ___ illumination with binocular viewing conditions

First phase

What phase:

is designed to correct the spherical element of the refractive error It should be remembered that, although astigmatism is often present, a refractive error may be entirely spherical

Second phase

What phase: determination of the astigmatic error

Third phase

What phase: involves the balancing and/or modification of the refractive correction to ensure optimal visual performance and patient comfort

Plano

Equivalent sphere if vision is: 6/5

0.25 to 0.50DS

Equivalent sphere if vision is: 6/6

0.50 to 0.75

Equivalent sphere if vision is: 6/9

0.75 to 1.00DS

Equivalent sphere if vision is: 6/12

1.00 to 1.25DS

Equivalent sphere if vision is: 6/18

1.25 to 1.50DS

Equivalent sphere if vision is: 6/24

1.50 to 1.75DS

Equivalent sphere if vision is: 6/36

1.00 to 1.25DC

Equivalent cyl if vision is: 6/9

1.25 to 1.75DC

Equivalent cyl if vision is: 6/12

1.75 to 2.25DC

Equivalent cyl if vision is: 6/18

2.50 to 3.00DC

Equivalent cyl if vision is: 6/24

3.00 to 4.00DC

Equivalent cyl if vision is: 6/36

2.00D

Estimated spherical refractive error if farpoint is 50cm

4.00D

Estimated spherical refractive error if farpoint is 25cm

6.00D

Estimated spherical refractive error if farpoint is 16.7cm

8.00D

Estimated spherical refractive error if farpoint is 12.5cm

10.00D

Estimated spherical refractive error if farpoint is 10cm

12.00D

Estimated spherical refractive error if farpoint is 8.3cm

+3.00

Average Rx at age 3 mos

+2.50

Average Rx at age 6 mos

+2.25

Average Rx at age 9 mos

+2.00

Average Rx at age 1 yr

+1.50

Average Rx at age 18 mos

+1.25

Average Rx at age 2 yrs

+1.00

Average Rx at age 3 yrs

+0.50

Average Rx at age 4yrs

+0.50

Average Rx at age 5yrs

+0.50

Average Rx at age 6yrs

Near add

Usually is in the form of plus over the distance refraction

Near Rx

to provide a correction that renders vision clear and comfortable at the desired near distance

Age

Occupation / Working distance

Amplitude of accommodation

3 basis that will influence amount of near add

Myopia

What refractive error require a weaker or lesser near add

Hyperopia

What refractive error require more or higher near add

higher

If a person requires nearer than 16 inches working distance, it requires higher/lesser add?

lesser

If a person requires farther than 16 inches working distance, it requires higher/lesser add?

True

T/F: A myopic person can remove their distance spectacles if they want to see at a close distance

· Non-responsive or non-communicative patients

· When objective and subjective data do not correlate

Indications when doing cycloplegic refraction

· Indications of high hyperopia

· Large esophoria or esotropia

· Small pupils for age

· Low amplitude of accommodation for age

· Fluctuations of accommodation

Syndrome of Findings to perform cyclorefraction

Cyclogyl (cyclopentolate)

Drug of choice for cycloplegic refractions of children

Cyclogyl (cyclopentolate)

Drug that is fairly potent and fairly fast

Available in 0.5%, 1% and 2% concentrations

Mydriacyl (tropicamide)

· Primary use is for dilation

· Rapid acting

· Provides a weak cycloplegia

· Short duration

Mydriacyl (tropicamide)

- Available in 0.5% and 1% concentrations

- Use 1 gtt 1%, wait 5 minutes, 1 gtt, wait 5 min, 1 gtt

- Total of 3 drops for cycloplegic refraction

Cyclogyl (cyclopentolate)

· Use 1 gtt of 1%, wait 5 minutes, then add second gtt

· Wait 30-45 minutes

Convex (+)

____ lenses lessens eso-deviation but exaggerates exo-deviation

Concave (-)

____ lenses lessens exo-deviation but exaggerates eso-deviation

Hyperopia with Exophoria

give minimum plus tolerable to bring phoria within acceptable range

Myopia with Exophoria

give maximum minus tolerable to bring phoria within acceptable range

Hyperopia with Esophoria

give maximum plus tolerable to bring the phoria closest to ortho (do not over plus to induce exophoria)

Myopia with Esophoria

give minimum minus tolerable to bring the phoria closest to ortho

1. Fogging Technique

2. Unfogging Technique

3. Finalizing the Sphere (Bichrome)

4. Sphere Use to Fog

5. Determination of Astigmatism

- determination of cylinder axis

- determination of cylinder amount

6. Refining the Cylinder Axis

- Bracketing method

- Cross-cylinder method

7. Refining the Cylinder Amount

8. Final Prescription

Clinical Procedure of Subjective Refraction

FOGGING TECHNIQUE

non-cycloplegic technique to relax accommodation

FOGGING TECHNIQUE

· To make sure accommodation is relaxed and ensure that the image will be formed in front of the retina (artificially myopic)

myopic

In fogging technique, you are making the px artificially (emmetropic, myopic, hyperopic)

Fogging technique

· With the image in this position any effort to accommodation will result in poorer vision rather than better

1. Add (+) lenses in 0.25 D steps until the biggest letter becomes blurred

2. Gross retinoscopy finding (+1.50 to +2.00 )

3. Sudden fog +2.00 D

3 ways to fog

new lens placed before removing previous

Rules in changing lenses in plus lenses

remove previous before new lens

Rules in changing lenses in minus lenses

Fogging lens

Highest plus (+) lens that makes the 20/200 blurred

+1.00

If the Px with subnormal visual acuity, add ____ to confirm the refractive status

True

T/F: If the px is myopic and has subnormal visual acuity, no fog is required

False

T/F: If the px is myopic and has subnormal visual acuity, fog is required

False

T/F: If the px is hyperopic and has subnormal visual acuity, no fog is required

True

T/F: If the px is hyperopic and has subnormal visual acuity, fog is required

Unfogging technique

· Decrease plus (+) lens in 0.25 D steps

· Endpoint criterion: strongest plus or weakest minus for best visual acuity

· Best line: smallest line of best vision

· Not all pxs will be able to reach 20/20

Unfogging technique

This is the step wherein you put the light rays exactly on the retina after making it in front of retina

FINALIZING THE SPHERE

(DUOCHROME / BICHROME / RED-GREEN TEST)

A technique for checking the Sphere power

Red-green test

· works on the principle that the wavelengths of red and green light are focused slightly differently by the eye, red being closer to the retina with short sight and green focused closer to the retina in long sight.

True

T/F: In shortsighted / nearsighted / long eye, the red wavelength is nearer the retina

False

T/F: In shortsighted / nearsighted / long eye, the green wavelength is nearer the retina

False

T/F: In longsighted / farsighted / short eye, the red wavelength is nearer the retina

True

T/F: In longsighted / farsighted / short eye, the green wavelength is nearer the retina

Emmetropia

Refractive condition if the yellow wavelength in duochrome test is exactly on the retina

Hyperopia

Refractive condition wherein green wavelength in duochrome test is nearer the retina

Myopia

Refractive condition wherein red wavelength in duochrome test is nearer the retina

Yellow

What wavelength color (the color that we want to put in the retina) is dioptrically halfway between green and red)?

1. Colebrooke Astigmatic Dial

2. Astigmatic fan dial

3. Clock dial

3 ways to determine astigmatism

Flip-cross technique

another term for JCC technique

cylinder, sphere

The cross cylinder is a spherocylindical lens in which the power of the ____ is twice the power of the _____ and of the opposite sign

Jackson Crossed-Cylinder

It is a combination of two cylinders of equal strength but of opposite signs

+0.50 DS = -1.00DC

-0.50 DS = +1.00DC

What is sphcyl of JCC

Near point range

In reading range, what is the point that the patient hold the near card at their preferred reading distance, and then ask them to move the card toward them until the target blurs

Far point of the range

In reading range, what is the point the patient is asked to push the card away until the target blurs

ideal reading range

preferred reading distance midway between these two points.

A. Equalization test with FOG and NO FOG

1. Prism Dissociation

2. Alternate occlusion

What are the tests for binocular balancing?

3 prism BD OD, 3 prism BU OS

In prism dissociation, what prisms you put over OD and OS

plus, clearer

In prism dissociation, when the two image is not equally clear, you add (plus/minus) lens over (clearer/blurry) eye until equally clear

plus, no

In Equalization test with no fog, the endpoint must be most (plus/minus) power that caused (no/with) blur

True

T/F: You always put plus lens when doing binocular balancing

True

T/F: In bichrome test as a binocular endpoint test, you do it binocularly open and monocularly done

equal target

In bichrome test as a binocular endpoint test, if the target on upper is red darker and equal in lower target, put plus lens on ____

green darker target

In bichrome test as a binocular endpoint test, if the target on upper is green darker and equal in lower target, put plus lens on ____