Opaque intraocular lens implantation

We read with great interest the recent article by Lee et al,¹ who described their clinical experience with three patients who underwent primary implantation of Morcher (Stuttgart, Germany) occlusive intraocular lenses (IOLs) across a variety of neuroophthalmic indications. We hope to offer some further insight into these clinical observations in the context of our ongoing research into occlusive IOLs. We feel such a discussion may be of benefit to ophthalmologists managing this group of patients.

Lee et al describe a patient with intractable diplopia who underwent clear lens extraction with implantation of an 80D 6 mm Morcher occlusive IOL, followed by a second procedure to augment occlusion within the scotopic pupillary margin using two Morcher partial aniridia implants (50C) and a third procedure to implant a Morcher 80D occlusive IOL with a 10 mm optic.¹ This patient was able to perceive light despite four anatomically continuous occlusive intraocular devices spanning the pupillary aperture. The authors interpret this to suggest the route of postoperative light entry into the eye must be across the intact sclera. Our research indicates a more likely mechanism to explain this perception of light, an understanding of which may be critical to a satisfactory outcome in this group of patients.

We initially reported the serendipitous discovery of successful macular imaging using a combined confocal laser scanning ophthalmoscopy/optical coherence tomography imaging system through the Morcher 85F occlusive IOL implanted in a patient with visual confusion.² We analyzed the transmission spectra of all Morcher occlusive IOLs to clarify the mechanism behind this observation, discovering that whilst wavelengths of light below 740 nm were occluded entirely by the occlusive IOL, there was an exponential increase in light transmission above 750 nm, with approximately 50% of light transmitted at 780 nm and 100% of light transmitted at wavelengths longer than 820 nm through the Morcher occlusive IOL.³ This explained the acquisition of high quality images with combined confocal laser scanning ophthalmoscopy/optical coherence tomography imaging systems which use a near infrared superluminescent diode as their light source.

Near infrared light activates photopigments in long wavelength red cone photoreceptors, resulting in light perception, provided that the stimulus of light is sufficiently bright. Photopic conditions and sources of light with a rich near infrared component are likely to be perceived by patients with near infrared-transmitting occlusive IOLs produced by Morcher. This near infrared window of transmission is the likely primary mechanism underlying refractory light perception in patients implanted with Morcher occlusive IOLs, rather than trans-scleral transmission of light through the intact sclerochoroidal tunic, as suggested.

Light perception across a near infrared-transmitting occlusive IOL must be considered a possibility by ophthalmologists in patients undergoing primary implantation with a Morcher occlusive IOL, and patients should be appropriately counseled preoperatively during the process of informed consent. As Lee et al state, patients with neuro-ophthalmic disorders may be very sensitive to any perception of light in the affected eye. Therefore, absolute light occlusion is the primary goal of treatment in this group, and may be critical to a satisfactory clinical outcome for the patient.

The authors report the use of Morcher partial aniridia castellated rings to augment light occlusion around the optic in cases with suspected light leakage due to mesopic or scotopic pupillary dilatation beyond the occlusive optic. Morcher produce occlusive IOLs by adding a tint to monomers prior to polymerization to polymethylmethacrylate.⁴ Morcher partial aniridia castellated rings (50C, 50E, 50F, 96C, 96F, 96E, 96G) are produced from the same material used to manufacture the Morcher range of occlusive IOLs (80D, 81D, 34D, 81F, 85F), so can be considered to transmit near infrared light identically.³ Whilst we agree that partial aniridia rings may augment occlusion of light, they cannot create absolute occlusion because of the optical properties of the materials from which they are manufactured, even in the presence of complete and contiguous anatomical occlusion due to apposition of the individual devices.

If a near infrared-transmitting Morcher occlusive IOL (81D, 85F, 34D) with a 6–7 mm occlusive optic is insufficient to produce satisfactory occlusion of light, we suggest that using Morcher 80D IOLs with a 10 mm optic is preferable to using partial aniridia implants, which may not be stable enough to augment occlusion even with overlapping castellations. Both of these occlusive strategies will not prevent occlusion of near infrared light. Multiple Morcher occlusive intraocular devices, whilst removing nonoccluded regions between prostheses, would not add any occlusive value beyond attenuating the intensity of near infrared light due to optical refections from their anterior interfaces. A single Morcher occlusive IOL is sufficient to occlude an intense, broad spectrum light source with an output irradiance of 3.73 × 10³ mW/cm² within the visible spectrum below 750 nm, with an exponential increase in transmission at longer wavelengths.

A distinction has emerged between the Morcher range of occlusive IOLs which transmit near infrared light, the occlusive polymethylmethacrylate IOL (MS 612, Dr Schmidt Intraocularlinsen GmbH, Sankt Augustin, Germany), and the occlusive iris-claw IOL (Artisan 201, Ophtec, Boca Raton, FL, USA) which are occlusive to all wavelengths of light.⁴ Therefore, the alternative surgical approach in this setting is to implant an iris-claw occlusive IOL, which has the dual advantage of achieving complete pupillary occlusion, with the use of intracameral Miochol intraoperatively prior to enclavation, making preoperative scotopic pupillometry irrelevant, and simultaneously occluding all wavelengths of light, including in the near infrared range, achieving a more robust state of light occlusion.⁴

We agree that the intraocular risks associated iris fixation such as uveitis, glaucoma, pigment dispersion syndrome, and endothelial cell loss make this implant less attractive as a primary occlusive strategy, but it can offer more definitive occlusion should other black IOLs fail to control symptoms. The MS 612 occlusive IOL should be considered in patients in whom preoperative scotopic pupillometry is appropriate for a 6 mm occlusive optic and robust occlusion of light is essential. This implant will not transmit near infrared light, even under intense photopic conditions.⁴

The third reported case in the series describes a patient with compressive optic neuropathy occurring secondary to a displaced intracranial vascular clip for a posterior communicating artery aneurysm. Intriguingly, this patient did not perceive light after implantation of a near infrared-transmitting IOL. This may be due to preferential loss of red perception typical of optic neuropathies, with impairment of the ability to detect near infrared light using long wavelength red cone photoreceptors and their connecting retinal ganglion cells. In the setting of an optic neuropathy, occlusion of visible spectrum light by the Morcher occlusive IOL may have been sufficient to occlude all light perception. A near infrared-transmitting occlusive IOL may be the prosthesis of choice for primary occlusion in these patients, provided red color perception is impaired on the Farnsworth-Munsell 100 hue test preoperatively. This will permit combined confocal laser scanning ophthalmoscopy/optical coherence tomography imaging for posterior segment examination without risking refractory light perception.

We hope this discussion aids the ophthalmologist caring for patients eligible for occlusive IOL implantation, adding to the clinical lessons reported by Lee et al.¹ Patient factors must be considered when selecting the appropriate primary occlusive intraocular implant to use in each case, and when considering the optimum surgical strategy for secondary procedures should the patient experience refractory light perception through the primary occlusive implant. Understanding the mechanisms of light transmission across occlusive IOLs is critical to ensuring a satisfactory clinical outcome in each eligible patient.