How is IOL power calculated in cataract surgery?

The measured transit time is converted to a distance using the formula d=t/v Where d is the distance, t is the time and v is the velocity. Two types of A-scan ultrasound biometry are currently in use. The first is contact applanation biometry. This technique requires placing an ultrasound probe on the central cornea.

Can high myopia be corrected with cataract surgery?

Cataract surgery is arguably the most powerful refractive surgery because the new lens implant can correct just about any degree of hyperopia, myopia, astigmatism and even presbyopia at the time of surgery.

What is the average power of IOL?

Due to anatomical variations in the population such as differences in eye length, corneal curvature (which affects corneal power), and refractive error, values for IOL powers vary over a broad range. Typical range of powers for IOLs is 5 D to 30 D in steps of 0.5 D for the most common lenses in the range.

Can high myopia cause cataract?

Unfortunately, patients with high myopia can develop cataracts earlier than those with no refractive errors, perhaps with visible cataracts appearing before 60. They’re about 3 times more likely to develop cataracts than those without, and recovery from cataract surgery is worse.

When to do IOL calculations in highly myopic eyes?

If your patient has an axial length of at least 30 mm or more than 15 D of myopia, be warned that the IOL power calculations, as well as the surgery, will be more challenging, as seen in Figure 1. The first consideration is to ensure that the posterior segment is free from dangerous pathology that could lead to vision loss.

How big should myopia be for cataract surgery?

For these patients with very long axial lengths and extreme levels of myopia, cataract surgery can be life-changing, but it is also quite challenging. If your patient has an axial length of at least 30 mm or more than 15 D of myopia, be warned that the IOL power calculations, as well as the surgery, will be more challenging, as seen in Figure 1.

How to calculate the power of an intraocular lens?

Wang L, et al. Optimizing intraocular lens power calculations in eyes with axial lengths above 25.0 mm. JCRS 2011; 37:2018-2027. One working theory is that optical biometry may exhibit a systematic error in the measurement of axial length that increases in a linear fashion.

Can a negative IOL be used for cataract?

The IOL power estimation is not nearly as accurate in these eyes with extreme axial lengths. Absolutely do not use the print-out of third generation formulae from your biometer. These patients will often have a negative power IOL and the lens design will be a meniscus type.