Preoperative Measurements and Intraocular Lens

Preoperative Measurements and Intraocular Lens Calculations
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Figure 5-2. The IOLMaster laser tomography AL measurement instrument. (A) Side view. (B) Front view.
Figure 5-3. Immersion technique setup for patient in a normal
ophthalmic examination chair.
lulose (Goniosol) in Dacriose solution. Once the eye is
anesthetized topically, the scleral shell is gently placed
between the lids and filled three-quarters full with
the solution. Any air bubbles should be vacuumed
with a short silicone tube attached to a syringe. The
latter can also be used to remove the solution at the
completion of the procedure. The ultrasound probe
is placed into the solution and positioned parallel to
the axis of the eye (Figure 5-4). Axiality is judged by
watching for the correct spike patterns on the oscilloscope screen as the probe position is adjusted. Many
find the Prager Shell [ESI, Inc, Plymouth, Minn) easier
to use for immersion.
Figure 5-4. Immersion technique showing the probe in the
Ossoinig shell filled with Goniosol.
WARNING
If the AL is very difficult to obtain and the eye
appears to have a length greater than 25 mm,
suspect a staphyloma. By direct ophthalmoscopy (with patient fixating on cross-hair target),
measure the distance from the target (macula) to
the edge of the optic nerve (in disc diameters).
B-scan exam is then performed to measure the
AL at that distance from the edge of the optic
nerve shadow (Figure 5-5).
WARNING
When measuring an eye containing an IOL,
ignore multiple reduplication echoes noted in the
vitreous space, which are caused by the IOL.