Mild over-minus power (0.25 to 1.00 D) can make distance targets appear subjectively darker and, therefore, falsely clearer to the patient.

Denning CHAPTER CONTENTS Retinoscopy Binocular Fog Manifest Refraction Binocular Balancing Trial Frame Refraction Cycloplegic Retinoscopy and Refraction Keratometry Computerized Corneal Topography Keratoscopy Pachymetry Specular Microscopy Ultrasonic Scanning High-Frequency Anterior Segment Ultrasound Biomicroscopy Contrast Sensitivity Testing Suggested Readings B efore undergoing refractive surgery, a candidates refractive error and other preoperative data, such as that from pachymetry and topography, must be evaluated to ensure consistent and accurate surgical results.

Likewise, postoperative data need to be evaluated to decrease the likelihood of complications and to increase the possibility of favorable surgical results.

Autorefraction may provide a useful starting point for baseline preoperative refraction but should not be used for postoperative testing because it often gives erroneous results ( Fig.

Figure 61 The autorefractor by Humphrey gives spectacle refractive error and K values.

RETINOSCOPY Indications starting point for determination of a patients manifest refractive error (required of all refractive surgery candidates) Methods Enter the correct distance pupil diameter into the phoropter.

Place the phoropter in front of the patient, making sure it is level with the patients head.

Present the 2060 line of Snellens chart to each individual eye.

If the line is too blurry to read with either eye, the patient is adequately fogged.) Present a 20400 distance target (e.g., the E from Snellens chart) to the patient for fixation using both eyes (OU).

Perform retinoscopy one eye at a time while OU are unoccluded.

Do not remove the retinoscopic working-distance lenses (usually 1.50 D) from the phoropter (can trigger patient accommodation).

Adjust the working-distance lenses accordingly if you perform retinoscopy particularly close to or far from the phoropter.

Record the retinoscopic findings for comparison with manifest refraction results.

Note the retinoscopic reflex (should be bright and clear, not dull).

Note any scissoring of the reflex motion (a hallmark sign of keratoconus).

BINOCULAR FOG MANIFEST REFRACTION Myopia determination of refractive error with a phoropter after retinoscopy (for all patients) Methods Follow these steps carefully to reduce chances of over-minus refractive results.

Initially, fog the right eye (OD) by 1.50 D and the left (OS) by 3.00 D.

Note that myopes can easily accept too much minus power for their manifest refraction endpoint if not properly fogged (results in postoperative overcorrection).

If retinoscopy immediately preceded manifest refraction, OD should already be fogged and so simply add another 1.50 D over OS to complete the initial fogging (see section on Retinoscopy).

With both of the patients eyes unoccluded, present the isolated 2060 line from Snellens chart.

Inform the patient that vision for OU should be fuzzy, with vision for the left eye being extremely fuzzy.

Patients should guess at letters during the exam if unsure).

Emphasize the importance of keeping OU open for the duration of testing.

Ask the patient to read the acuity line that is presented with each 0.25 D decrease in plus-sphere power.

Stop decreasing plus-sphere power when the patient is able to just see the smallest achievable acuity line without noticing any minification of the letters.

Refine the cylinder amount and axis OD using the phoropters Jackson crossed cylinder (JCC) and one line larger than the patients smallest achievable acuity line as the target.

Slowly step the patient out of plus power, asking the patient if the final step-down lenses make the target line clearer and easier to read or just smaller and darker (minified).

If the patient notices minification of the letters but acuity does not improve, then the patient is probably over-minused in power.

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