Irregular corneas stand to benefit from small-aperture IOL design

December 11, 2020

The principle of pinhole optics at work in the IC-8 IOL overcomes visual disturbances associated with corneal disease and provides a functional range of vision.

The simple, age-old and well-accepted principle of pinhole optics allows for an extended depth of focus. To achieve a more functional continuum of vision, the IC-8 IOL (AcuFocus; see Figure 1) harnesses pinhole optics with a small-aperture design—1.36 mm—to provide good uncorrected distance visual acuity (UDVA) and better uncorrected intermediate visual acuity (UIVA) than standard monofocal IOLs in patients undergoing cataract surgery.1,2

Embedded with an opaque mini-ring, the device is a hydrophobic acrylic single-piece implant. Previous reports have described the IC-8 IOL as forgiving, in part due to its broad refractive landing zone that allows it to tolerate up 1.00 D of defocus and up to 1.50 D of corneal astigmatism.1,3

Implanted cataract patients enjoy high-quality, sharp vision and less concern with photic phenomena compared with multifocal and accommodating technologies.4 The IC-8 IOL has also been found to enhance vision at all distances, with improved visual acuities and a broad range of continuous functional vision.

Importantly, patients have shown superior intermediate vision and binocular mesopic contrast sensitivity comparable to the other lenses.4 The lens is cleared for use in Europe and Asia and currently in clinical trials in the United States.

The not-so-normal cornea

It is known that a small aperture can reduce the higher-order aberrations (HOAs) that are associated with irregular corneas, providing improved central visual acuity via the pinhole optics principle. Therefore, our scientific team (Prof. Dr W. J. Mayer, Dr M. Shajari and myself, Dr M. J. Mackert) at the University of Munich, Germany, sought to investigate the IC-8 IOL, not in conjunction with routine cataract surgery but rather for lens surgery in eyes with severe corneal irregularities due to advanced keratoconus or after penetrating keratoplasty, for example.

Individuals with these conditions have a significant reduction in visual acuity and poor visual quality due to HOAs. Although rigid gas-permeable contact lenses can provide some improvement, these corneal diseases in particular are often accompanied by contact lens intolerance.

Laser treatment using topography-guided photorefractive keratectomy with or without mitomycin C or crosslinking may be an alternative solution to treat these corneas before lens surgery; however, the latter is contraindicated in many corneal diseases. It is even more difficult to calculate the correct IOL for cataract surgery in these irregular corneas.

A pinhole implant specifically designed for cases with corneal irregularities has previously been shown to result in excellent visual results as an add-on implant.5–7 This implant, the XtraFocus (Morcher), has no optical power and, unlike the IC-8 IOL, was not designed to function as an enhanced depth-of-focus IOL. The IC-8 IOL is placed directly in the capsular bag and can be used during cataract surgery.

For the study we recently reported in the Journal of Cataract & Refractive Surgery, we evaluated subjective and objective visual outcomes following implantation of the small-aperture IOL in 17 eyes of 17 patients with severe corneal irregularities.8 As we expected, the IC-8 IOL reduced the visual distortion caused by corneal irregularities, leading to better visual perception.9

The IOL, which is typically a monocular implant, was implanted under topical anaesthesia using a 2.8-mm clear corneal incision. Patients with active disease such as progressive keratoconus were excluded, as well as those with central corneal scarring, pseudoexfoliation, glaucoma, maculopathies or a reduced endothelial cell count (< 1800 cells/mm2).

In our cohort with corneal irregularities, we observed an increase in UDVA, UIVA and near (UNVA) vision with the IC-8 IOL versus a monofocal IOL in healthy eyes; we also observed an extended depth of focus (Figures 2–3; preliminary results presented at DGII 2019 in Berlin).10

Unlike other multifocal IOLs, in which the complex optic can lead to an increase in optical phenomena such as glare and halo,11,12 especially in patients with corneal irregularities, the pinhole system improves visual quality while reducing the occurrence of these phenomena.

Safe implant, happy patients

As it stands, in eyes with severe corneal irregularities, the pinhole IOL is not implanted primarily to achieve an extended depth of focus but to increase visual acuity and quality. In our cohort, 16 of the 17 eyes experienced an improvement in postoperative corrected distance visual acuity. This result is likely due to the IOL’s attributes and not because of the removal of existing opacities in the natural lens.

Patients indicated a high satisfaction rate on the VFQ-25 questionnaire, reporting that they were better able to perform daily tasks. They experienced a clear increase in their near and distance reading ability as well as improved visual quality due to the implant’s ability to overcome the optical phenomenon associated with irregular corneas. The small-aperture IOL was shown to be safe in these patients.

A challenge remains in terms of accurate IOL power calculation in these severely irregular eyes. We observed an extremely high variance in our cohort with average keratometry ranging from 37.00 D to 55.00 D and astigmatism of up to 8 D within the central 3-mm corneal zone. IOL power calculation using the traditional formulas was not possible; therefore, a myopic outcome was targeted for these patients. We found that the Haigis formula provided the most accurate results and the smallest mean absolute error, and a substantial number of eyes of eyes had a myopic outcome with an average spherical equivalent of 1.22 D after 3 months.13

Conclusion

Patients with corneal diseases such as keratoconus or scarring after herpes keratitis, and up to 20% of patients after penetrating keratoplasty have irregular corneal astigmatism. The associated HOAs cause a significant loss of vision in these individuals. Based on our results, the IC-8 represents an excellent option to improve functional vision in patients with corneal irregularities.

This is a completely different approach than that originally conceived for this small-aperture implant. By applying a simple pinhole concept we can provide good visual outcomes for patients who previously were not candidates for premium IOL implantation.

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Marc J. Mackert, FEBO
E: Marc.Mackert@med.uni-muenchen.de
Dr Mackert is the head of the glaucoma department at the hospital of the University of Munich, Germany. The study highlighted in this article was supported by Acufocus.

References

  1. Dick HB, Piovella M, Vukich J, et al. Prospective multicenter trial of a small-aperture intraocular lens in cataract surgery. J Cataract Refract Surg. 2017;43:956–968.
  2. Hooshmand J, Allen P, Huynh T, et al. Small aperture IC-8 intraocular lens in cataract patients: achieving extended depth of focus through small aperture optics. Eye (Lond). 2019;33:1096–1103.
  3. Ang RE. Visual performance of a small-aperture intraocular lens: first comparison of results after contralateral and bilateral implantation. J Refract Surg. 2020;36:12–19.
  4. Pepose J. Evaluating visual performance of small-aperture, accommodating, and multifocal IOLs. Presented at AAO 2019; October 11–15; San Francisco, CA.
  5. Trindade BLC, Trindade FC, Trindade CLC, Santhiago MR. Phacoemulsification with intraocular pinhole implantation associated with Descemet membrane endothelial keratoplasty to treat failed full-thickness graft with dense cataract. J Cataract Refract Surg. 2018;44:1280–1283.
  6. Trindade CC, Trindade BC, Trindade FC, et al. New pinhole sulcus implant for the correction of irregular corneal astigmatism. J Cataract Refract Surg. 2017;43:1297–1306.
  7. Tsaousis KT, Werner L, Trindade CLC, et al. Assessment of a novel pinhole supplementary implant for sulcus fixation in pseudophakic cadaver eyes. Eye (Lond). 2018;32:637–645.
  8. Shajari M, Mackert MJ, Langer J, et al. Safety and efficacy of a small-aperture capsular bag-fixated intraocular lens in eyes with severe corneal irregularities. J Cataract Refract Surg. 2020;46:188–192.
  9. Schultz T, Dick HB. Small-aperture intraocular lens implantation in a patient with an irregular cornea. J Refract Surg. 2016;32:706–708.
  10. Dick HB, Elling M, Schultz T. Binocular and monocular implantation of small-aperture intraocular lenses in cataract surgery. J Refract Surg. 2018;34:629–631.
  11. Gil MA, Varon C, Rosello N, et al. Visual acuity, contrast sensitivity, subjective quality of vision, and quality of life with 4 different multifocal IOLs. Eur J Ophthalmol. 2012;22:175–187.
  12. Bellucci R. Multifocal intraocular lenses. Curr Opin Ophthalmol. 2005;16:33–37.
  13. Haigis W, Lege B, Miller N, Schneider B. Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis. Graefes Arch Clin Exp Ophthalmol. 2000;238:765–773.