Keratoconus is a multifactorial corneal ectatic disease. In aging patients with an existing keratoconus and the additional development of cataract, therapeutic and refractive management is even more complex.
The IC-8 intraocular lens (IOL) (AcuFocus, Inc.) is a single-piece hydrophobic acrylic posterior chamber IOL with a circular mask and a small 1.36 mm central aperture. This pinhole mini-ring design in the center is used to increase a patient's range of vision by adjusting the focus of light rays that enter the eye. It combines small-aperture optics with a monofocal IOL.1,A The current main application of the IC-8 is presbyopia correction. Simultaneously, the pinhole effect enables an increased visual acuity in patients with irregular astigmatism like in keratoconus by blocking the irregular refracted light beams.
A 44-year-old man presented to our clinic with keratoconus and cataract in both eyes. Despite the relatively young age for cataract, there was no history of trauma or uveitis. Before developing the cataract in September 2018, the patient regularly used multifocal spectacles with subjectively satisfactory results. Although the patient did not report any previous diseases, there is the possibility of a predisposition such as an undetected atopy. This could give an explanation for the early onset of a cataract. He stated that he did not use any contact lenses for decades because they were not well tolerated.
On the first examination in our clinic a nuclear cataract and keratoconus (R > L) in both eyes was diagnosed. The preoperative corrected distance visual acuity was 0.30 diopter (D) for the right eye (+3.0/−1.25 @ 30) and 0.50 D (+1.25/−0.75 @ 147) for the left eye. The uncorrected distance visual acuity was 0.20 D and 0.50 D, respectively. The diagnosis of keratoconus was assessed by corneal tomography. The posterior elevation map of the right eye showed a best fit sphere fit zone of 8.0 mm with 6.21 mm best fit sphere radius; moreover, a tongue-like pattern with high posterior elevation of >20 µm could be identified. Figures 1 and 2 show the tomographic, instantaneous corneal maps for the right and left eye.2 A summary of preoperative tomographic parameters is shown in Table 1. For IC-8 IOL power calculation the Barrett Universal II Formula was used for both eyes.3,4 This fourth-generation formula is the most accurate formula for axial lengths of 22.0 mm and more and, therefore, was considered accurate for biometry in both eyes (right eye, 22.93 mm and left eye, 22.92 mm).3 Because refractive surprises may be caused by a high irregular astigmatism, a target refraction of −0.75 D on the right eye with an IOL power of 24.50 D was used. For the left eye, target refraction emmetropia was planned using an IOL power of 24.00 D. Nevertheless, other studies have shown that an inaccuracy in IOL power calculation has to be expected and can still lead to a refractive shift.5 The patient had uneventful femtosecond laser–assisted cataract surgery (LDV Z8, Zeimer) with implantation of an IC-8 IOL into the right eye (Figure 3). Two weeks later, the left eye had femtosecond laser–assisted cataract surgery with implantation of an aspheric IOL inducing zero spherical aberrations. All surgeries followed a standardized protocol and were performed by the same surgeon (S.L.).
At the last follow-up, 21 weeks after treatment, the spherical equivalent of the right eye was +0.75 D, although we aimed for an spherical equivalent of −0.75 D. On the left eye, we planned to achieve emmetropia while the patient shifted to +0.75 D. The patient presented postoperatively with corrected distance visual acuity at 4-month follow-up 0.90 D in the right eye (+1.75/−2.0 @ 50) and 0.90 D in the left eye (+1.25/− 0.75 @ 97). The uncorrected distance visual acuity at 4-month follow-up was 0.50 D in the right eye and 0.90 D in the left eye. A binocular contrast visual acuity test (Mesotest II, OCULUS Optikgeräte GmbH) showed 1:2 and 1:27 on glare sensitivity.
The IC-8 IOL features an implemented mask with a diameter of 3.32 mm and a central aperture with a 1.36 mm diameter creating a pinhole effect, which leads to an extended depth-of-focus by isolating focused central and paracentral rays through the central aperture to reduce higher-order aberration.6 Higher-order aberration induced by keratoconus can be very disturbing for patients, and thus, the primary aim of implanting the IC-8 IOL was to reduce these aberrations.
The irregularity of the cornea in keratoconus confronts us with less accuracy of the preoperative biometry and lens power calculation compared with healthy eyes. This aspect is described by a study by Leccisotti in which the authors stated a high number of intraoperative and postoperative IOL exchanges due to inaccurate calculations of the IOL power, which appeared more commonly in eyes with keratoconus stage II and higher.6 Both eyes presented with a small induced flattening of the superior cornea due to a superior surgical approach with a clear corneal 2.4 mm tunnel (Figure 1 and 2). According to the inferior–superior data, we observed an increase of +0.75 D in both eyes.
In keratoconus, some refractive characteristics are important: While the ectatic disease is progressing, the corneal shape becomes more and more prolate and the negative corneal asphericity increases. Furthermore, the astigmatism increases and becomes more and more irregular. Therefore, an aspheric lens inducing a negative spherical aberration as used in many patients to improve the postsurgical visual quality would be counter-productive in keratoconus eyes (and posthyperopic laser in situ keratomileusis eyes). Furthermore, toric IOLs will not address the irregular component of the corneal astigmatism in keratoconus and can lead to a limitation of the final acuity as described by Watson et al.2 The right and the left eyes had stage 2 keratoconus defined based on the Amsler–Krumeich classification. Therefore, we implanted the IC-8 IOL in the right eye due to the irregular cornea and an aspheric nontoric, monofocal IOL with an asphericity of zero (no induction of a negative spherical aberration as featured in most of the premium aspheric IOLs to compensate for the natural positive spherical aberration of the cornea) in the left eye.
Although the pinhole design in the IC-8 IOL seems to be more forgiving compared with the classic monofocal IOLs in terms of targeting refractive endpoints, it is recommended to plan the refractive outcome even more myopic to compensate for a postoperative hyperopic shift.A
The IC-8 IOL provides a reduction of up to 1.5 D of preexisting or surgically induced refractive astigmatism. The IC-8 IOL contributes to a reduction of up to 2.0 D of astigmatism because of its pinhole effect (pseudoaccomodation) as described by Ang.7 Therefore, the IC-8 monofocal IOL may be a good option for patients with keratoconus (or other corneal irregularities) with coexisting cataract.8 Because of a new Conformité Européenne-marked injector, the IC-8 IOL can be implanted through a 2.4 to 2.8 mm incision size. The advantage to using the femtosecond laser is the preciseness of the capsulorhexis and the fragmentation of the lens. Therefore, we have regular, minimal overlapping of the IOL optic due to the rhexis edge. In our experience, this results in a reduced risk for lens tilting or a dislocation due to irregular fibrosis of the capsules and a reduced risk for a capsule shrinking. This might enable better long-term predictability of the effective lens position, which is more important in customized lenses such as the IC-8 and multifocal IOLs.
There are some compromises to be aware of when implanting an IC-8 IOL. Although our patient did not show any complications or side effects, the manufacturer reported on possible side effects as halos or glare, which can appear at night, and low-contrast image quality. The implantation can cause difficulties in performing certain eye examinations and treatments such as retinal photocoagulation and results in low-quality retinal optical coherence tomography images. Objective refractive measurements after IC-8 IOL implantation are not possible. Some patients need time to adapt neural coordination between the eyes when different IOLs are implanted. Another limitation can be seen in higher costs, which are in average 6 times higher than for conventional monofocal IOLs.
The IC-8 IOL is only available since 2016 in Germany, and a wider range of clinical studies is required to enable adequate judgment.
In summary, the implantation of an IC-8 IOL in patients with keratoconus and cataract could be a safe and effective option to enable good postsurgical uncorrected and corrected visual acuity and quality.
1. Grabner G, Ang RE, Vilupuru S. The small-aperture IC-8 intraocular lens: a new concept for added depth of focus in cataract patients. Am J Ophthalmol 2015;160:1176–1184
2. Watson P, Anand S, Bhogal M, Gore D, Moriyama A, Pullum K, Haus S, Tuft SJ. Cataract surgery outcome in eyes with keratoconus, Br J Ophthalmol 2014;98:361–364
3. Kane JX, Van Heerden A, Atik A, Petsoglou C. Intraocular lens power formula accuracy: comparison of 7 formulas. J Cataract Refract Surg 2016;42:1490–1500
4. Barrett GD. Barrett Universal II Formula. Singapore, Asia-Pacific Association of Cataract and Refractive Surgeons. Available at: http://www.apacrs.org/barrett_universal2/
5. Frings A, Dulz S, Skevas C, Stemplewitz B, Linke SJ, Richard G, Wagenfeld L. Postoperative refractive error after phacovitrectomy for epiretinal membrane with and without macular oedema. Graefes Arch Exp Ophthalmol 2015;253:1097–1104
6. Leccisotti A. Refractive lens exchange in keratoconus. J Cataract Refract Surg 2016;32:742–746
7. Ang RE: Small-aperture intraocular lens tolerance to induced astigmatism. Clin Ophthalmol 2018;12:1659–1664
8. Schultz T, Dick HB. Small-aperture intraocular lens implantation in a patient with an irregular cornea, J Refract Surg 2016;32:706–708
OTHER CITED MATERIAL
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