#  Preoperative preparation with optical biometry 

 



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 After a thorough clinical exam to identify any relevant ocular comorbidities and establish an appropriate refractive aim, a crucial step for successful cataract surgery is optical biometry. This is the critical process of determining the proper intraocular lens (IOL) power for the patient’s needs. The IOL power is calculated based on the accurate measurement of the various physical characteristics of the eye, such as axial length, corneal keratometry, anterior chamber depth, and other parameters.

 For greatest accuracy, it is recommended that surgeons use high-quality optical biometry whenever possible. The latest swept-source OCT biometers have improved rates of success measuring through denser cataracts. Comparing measurements from different instruments is useful to confirm validity of the data, particularly if the two eyes are not highly symmetric. If there is a discrepancy, it alerts the surgeon to re-examine ocular comorbidities, repeat biometry, and/or reconsider IOL choices.

###  **Common factors that affect biometric accuracy**

 **Axial length:** Macular degeneration, strabismus, and opaque media can lead to poor fixation or difficulty measuring at the fovea. It is important that specific parameters on the biometers be set to account for conditions such as aphakia and silicone oil in the eye, in order to correctly calculate the axial length. Sometimes, A-scan ultrasound biometry is still necessary for white or brunescent cataracts that preclude measurement by optical biometry.

 **Keratometry:** Dry eyes, ectasia, corneal scarring, and previous surgeries (e.g., refractive surgery, trabeculectomy and others) can all lead to unreliable keratometry.

 **Effective lens position:** Pupil dilation status can affect the measured anterior chamber depth.

 **IOL formula:** Modern IOL calculation formulas, such as Barrett Universal II, Barrett True-K, Hill RBF, and Kane are more accurate than the previous generations. They provide more precise calculations of “effective lens position” derived from parameters such as anterior chamber depth, lens thickness, and corneal diameter, and artificial intelligence. The percentage of eyes that achieve the preoperative refractive aim significantly increases when these modern formulas are applied appropriately to the biometry data, particularly for long, short or post-refractive surgery eyes.