We had a few patients referred to our ophthalmic clinic with both cataract and keratoconus. Some intraocular lens(IOL) implantation didn't correct refractive errors in some of them completely. I want to know new methods and IOLs implantation in cataract surgery to correct refractive errors of keratoconus simultaneously.
In case of keratoconus the toric IOL implantation according to astigmatism due to keratoconus will be helpful
As long as the refractive error correlates with the keratometric measurements, a toric IOL works well. Intraoperative aberrometry helps even more. Still, in some patients, the best solution for crisp vision is a rigid contact lens.
Because the basic problem in keratoconus is in the cornea, a complete alleviation of refractive errors can not be expected from cataract surgery and IOL implantation. A toric IOL is helpful as much as the presence of regular astigmatism. If cataract does not preclude reliable subjective refraction, then toric IOL axis may be determined according to subjective refraction axis. Otherwise, both anterior and posterior corneal astigmatism should be considered for axis determination.
".,..both anterior and posterior corneal astigmatism should be considered for axis determination..."
Not only the posterior surface astigmatism plays a significant role in determination of the astigmatism power and axis or the toric IOL in keratoconus. Coma, which is the most dominant feature of the corneal optics in keratoconus, influences significantly both the power and the axis of the cylinder when only spherocylindrical correction (toric IOL) is an option. Ideally, corneal coma (both anterior and posterior) should be corrected first by custom ablation combined with CXL, while the regular total corneal astigmatism should be corrected by toric IOL. Unfortunately the available custom ablation and CXL options rarely allow the latter scenario, leaving the subjective cylinder power and axis as the most realistic information for the determination of the IOL cylinder.
According to what Dr.Stojanovic just mentioned, COMA is the major cause of irregular astigmatism induced by keratoconus.
You cannot correct coma with toric IOL, you can only "optimize" the astigmatism and the patient will remain with high order aberrations after the surgery.
If keratoconus is not progressive (and you don't need CXL), you can program a toric IOL implant exspecially if astigmatism is not completely irregular or scotopic pupil is small.
In case of high irregularity, in my opinion the best option to correct it simultaneously with cataract surgery, is to perform the first surgery implanting a single inferior intracorneal ring (according to the nomogram), correcting only topo-tomographic COMA-AXIS. After the implant, is recomended to wait up to 3 months for corneal astigmatism stability and perform a cataract surgery with a toric IOL on the residual ASTIGMATISM AXIS.
I reported to ESCRS in Barcelona this very interesting case not yet published, done one year ago with a very nice result, have a look on this link:
http://escrs.conference2web.com/content/25806/details?from_view=all&view_address=search%3Dgualdi
All the best
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