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Breaking down IOL stones in complex corneas, part 2

March 17, 2022

2 minute read


Biography: Farid is director of cornea, cataract, and refractive surgery and vice chair of the faculty of ophthalmology at the Gavin Herbert Eye Institute at UC Irvine.


Disclosures: Al-Mohtaseb declares having financial interests with Alcon, Bausch + Lomb, Carl Zeiss, CorneaGen, Novartis and Ocular Therapeutix. Farid is a consultant for Allergan, Bausch + Lomb, Bio-Tissue, Carl Zeiss Meditec, CorneaGen, Dompé, Johnson & Johnson Vision, Kala, Novartis, Orasis, Sun and Tarsus.


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Part two of this two-part blog looks at keratoconus, trauma, corneal dystrophies, lumps and bumps.

In patients with complex corneas, it is difficult to obtain accurate IOL calculations. To make these calculations more accurate and ensure hitting the refraction target, it helps to get more data points.

Zaina Al-Mohtaseb

Marjan Farid

In normal corneas, we obtain the corneal topography using a single topographer. Dr. Al-Mohtaseb’s practice uses the Galilei (Ziemer) while Dr. Farid prefers the Pentacam (Oculus) tomograph, both of which are based on Scheimpflug imaging. We measure biometrics with the Lenstar (Haag-Streit) and/or the IOLMaster 700 (Zeiss). The three main formulas we apply are Barrett (True-K for post-laser vision correction eyes and Universal II for all other eyes), Hill-RBF and Optimized Holladay 1.

For irregular eyes, however, the process changes as surveyors and biometers are created for normal corneas. For more information, see part one.

Keratoconus, trauma

A farsighted finding is more likely in keratoconic eyes with stiff corneas and higher posterior corneal astigmatism. There is greater variability when the anterior or posterior cornea is stiffer. Therefore, for these patients, we want to target myopia.

For corneal trauma and scarring, we need to determine if a corneal transplant is needed before cataract surgery. If there are peripheral scars with irregular astigmatism, we usually select a monofocal lens, looking at the central 3mm area to choose the right IOL power. This is another potential candidate patient population for the IC-8 (AcuFocus) IOL. However, if patients have previously worn hard contact lenses, we still advise them to continue wearing their contact lenses for optimal clarity.

Corneal dystrophies, lumps and bumps

In the context of corneal dystrophies, the cornea can be regularized by performing a superficial keratectomy. We then wait 1 to 3 months for the cornea and the topography to normalize before measuring the biometrics and finalizing the IOL power. We remove pathology before surgery and again wait for stabilization. We have seen situations in which patients with Salzmann nodules have toric implants and are very upset because the astigmatism irregularity was not identified prior to surgery and IOL planning.

The IC-8 Small Aperture IOL has a wavefront filtering design that eliminates unfocused peripheral light rays, allowing only central rays to focus on the retina. Studies have shown that the IC-8 IOL can provide up to 3D of extended depth of field and tolerate up to 1D of deviation from the spherical equivalent of target manifest refraction. The lens can attenuate up to 1.5 D of irregular astigmatism. The IC-8 IOL may soon be an option for these patients and allow them to benefit from an increased field of vision after cataract surgery.

The references:

Ang RE. Clin Ophthalmol. 2018;doi:10.2147/OPTH.S172557.

Dick HB, et al. J Refractory cataract surgery. 2017; doi:10.1016/j.jcrs.2017.04.038.

Grabner G, et al. Am J Ophthalmol. 2015;doi:10.1016/d. add.2015.08.017.

TuckerJ, et al. Am J Optom Physiol Opt. 1975; doi:10.1097/00006324-197501000-00002.