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Touch and Go: A-Scan Technique

Kurt Buzard MD FACS

Tulane University Medical School
University of Nevada Medical School
Buzard Eye Institute
Las Vegas Nevada

A-scan Tips

• Hand held scans are inherently inaccurate
• Remember that accuracy to 0.5D requires about 150 micron A-scan accuracy
• This requires:
• precise positioning
• minimal or no pressure on cornea
• a wet cornea
• good spikes

A-scan Room

       

Storz A-scan Attached to Slitlamp

Remember that A-scans attached to tonometry arm will applanate the corne This can result in significant inaccuracy

Touch and Go Method

Before getting actual reading, try touching cornea and then retract until probe lifts off This gives the general range of readings to aim for Then attempt to get the number with good spikes

General rules

• The two eyes should usually match in terms of a-scans
• Assymmetrical refractions may reflect assymetrical a-scans
• For sulcus placement subtract 1 diopter
• For piggyback IOL add 1 diopter
• Aim for -1.5 to -1.75 D for monovision

A-scan Spikes

Keep probe slightly nasal and central Clean spikes indicate that reading does not go through iris First and last spike must be full height or bad reading

IOL Calculation

The Hoffer program has been very reliable in our practice New features such as outcome analysis and personalized A constant make it our choice for accurate calculations

Keratometry

• Best measurement is manual
• Next best is Humphrey autokeratometer (not made anymore)
• Never use topographic k-readings
• Combined autorefractors/keratometers are just average for k-readings

Surgical Issues

• We do surgery 1 day to 1 week apart ... Think of patient in refractive terms, try ctl and possible monovision on other eye
• Better surgery results in more predictable results...faster surgery with complications can add many unnecessary postop visits and slow visual recovery
• Use astigmatically neutral surgery

After Surgery

• Three main issues:
  • Capsular opacification
  • Astigmatism
  • Spherical error
• We see at 1D, 2W and 1-2M
• Do astigmatism at slitlamp..ATR sooner / WTR later since it may degrade
• Do IOL exchange for spherical error

Summary

• Refractive phaco is a state of mind
• Losing on a few cases with reoperations will be repaid with many other happy patients without reops
• Think refractive! ... Early relaxing incisions...astigmatically neutral incisions...and ctl for spherical errors will increase satisfaction and decrease visits

Refractive Phaco Spherical Equivalent for CE/IOL

Six hundred patients, 1 year follow-up