SUBJECTIVE REFRACTION

At the end of this lecture, students should be able to

✓ Refine objective refractive findings to get the final prescription
✓ Derive a comfortable prescription that produces maximum visual acuity

Introduction

The goal of subjective refractive is to refine the objective findings through which the patient can see
comfortably. During subjective refraction, the examiner communicates with the patient and using the
patient’s response to the vision provided with various lenses to determine the optical correction that best suits
the patient. It is therefore only possible to perform subjective refraction with patients who can communicate
effectively with you.
You can begin your refraction from 4 different starting points:
– Retinoscopy results

– Autorefraction results

– Lensometry measurements

– From scratch -with no objective measurements (beyond the scope of this lecture)

For the purpose of this lecture we will begin our subjective refraction from the retinoscopy results.
Subjective refraction overview
1. Initial sphere check
2. Cylinder axis refinement
3. Cylinder power refinement
4. ±0.50 check
5. Repeat steps 1-4 for other eye
6. Binocular balance

Procedure
1. Explain the procedure to the patient.
2. Begin with the net retinoscopy sphere-cylinder before each eye. The patient’s distance PD should already
be set in the phoropter or trial frame, which should be level and positioned appropriately.
3. The Subjective refractive traditionally begins on the right eye. Occlude the left eye.

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 4. Determine the best sphere. This must be performed to ensure that the circle of least confusion is on the
retina prior to the use of the JCC. There are several ways in which this can be determined, the most
common of which are the fog/unfogging or plus/minus techniques and the use of the Duochrome target.
a. Fog / Unfogging: this technique has advantage that accommodation is well controlled when
examining young patients. The process of fogging the eye is to relax accomodation. To make sure
accomodation is relaxed, each eye is fogged by placing enough plus lens power in front of the eye.
The technique is particular easy when using a phoropter, as the lens changes can be made quickly and
easily.
If it were not for the existence of astigmatism, subjective refraction would be a relatively simple
procedure. All that would be necessary would be for the examiner to place enough plus lens power in
front of each eye to for vision to 6/12 or 6/9 and then reduce the power until clear vision was obtained.
You have to reduce the plus lens in 0.25D steps at a time, the patient will be able to read successively
smaller rows of letters until the 6/6 or possibly the 6/5 can be read.

NOTE: The end point criterion used in subjective refraction is the ‘maximum plus lens power for best
VA’ or least minus lens.

b. Astigmatic charts: when astigmatism is present, as it is in the great majority of eyes, the closest thing
to a point object is the circle of least confusion located at the dioptric midpoint between the horizontal
and vertical focal lines. The two most commonly used astigmatic charts are the clock dial and the
rotating T.
The examiner’s first job is to determine the correcting cylinder. This is done by first asking the patient if he
or she can see three lines in any or all the spokes.
To determine the axis of the correcting cylinder, the smaller of the clock number is multiplied by 30. if a
patient sees the 1 to 7 o’clock place your cylinder at 30. if the patient sees the 12 to 6 o’clock place your
cylinder at 180. keep adding minus 0.25D cylinder until all spokes are equally clear.

c. Jackson cross cylinder (JCC): The JCC often called the flip cylinder is used to refine cylinder power, it
is oriented in front of the refractor lens cell in such a way that the principal meridians of the crossed
cylinder are located parallel to the principal meridians of the correcting lens. Therefore, when the ±0.25D
crossed cylinder is used to refine cylinder power, in one position 0.25D of minus cylinder is added to the
power of the cylinder in the refractor, and in the other position 0.25D of minus cylinder power is

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 subtracted from cylinder in the refractor. The position is changed simply by flipping the crossed cylinder
lens over so that the patient looks through the opposite side.
The advantage of the JCC when refining cylinder power, is that it can add or subtract cylindrical power
relative to the correcting cylinder in the refractor without changing spherical power that is the same
spherical equivalent power is maintained throughout the test.
When the crossed cylinder is used to refine cylinder axis, it is oriented in front of the refractor lens cell
so that its two principal meridians are located at an angle of 450 from the two principal meridians of the
correcting lens. When the ±0.25D crossed cylinder is used to refine cylinder axis in one position the axis
of the combination (the correcting cylinder and crosses cylinder) is moved in one direction; when it is
flipped over to the other side, the position of the axis of the combination of the correcting cylinder and
the crossed cylinder is moved an equal amount in the opposite direction.

BINOCULAR BALANCING
The purpose of binocular balancing test is not to balance the visual acuity but to balance the state of
accommodation of the two eyes. The procedure used for balancing the state of accommodation for the two
eyes are often referred to as equalization tests or as binocular balancing test. You could do the test by
⚫ Balancing with little or no fog
◼ Prism dissociation
◼ Alternate occlusion
◼ Bichrome test

RECORDING

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