Introduction

Modern cataract surgery has achieved excellent central visual outcomes. The development of intraocular lenses (IOLs) has progressed from rigid monofocal implants to aspheric monofocal, extended-depth-of-focus (EDOF), multifocal and accommodating designs [1–3]. Nevertheless, important limitations persist: reduced twilight and night vision, glare, and impaired peripheral image quality [1,4].

One of the main reasons is the geometry of current IOLs. Almost all available IOLs have an optic diameter of 6.0 mm, often with an effective optical zone of only about 5.5 mm, and a symmetrical biconvex shape. In contrast, the natural crystalline lens has different anterior and posterior curvatures, with approximately one quarter of the refractive power located anteriorly and three quarters posteriorly [1]. This anatomical mismatch may explain the poorer peripheral optical performance and the ring-shaped reflexes observed clinically.

The purpose of this work is to:

1. Illustrate the optical limitations of current symmetric IOL designs using personal photographic and clinical experience;
2. present a diameter-adapted, posteriorly more convex and aspheric IOL concept developed by the author in 1993/94;
3. Review current developments in accommodative, dual-optic and modular IOL systems, including artificial capsular bag concepts;
4. Derive recommendations for future IOL design and for individualized optical rehabilitation.

Methods

Photographic documentation

Wide-field retinal imaging was performed with the Retcam system (Clarity Medical Systems), which is mainly used in paediatric ophthalmology, including screening for retinoblastoma. The contact optics provide peripheral illumination through a ring-shaped light source, allowing reflex-free fundus imaging up to approximately 160° [1].

Retcam photographs were obtained:

1. In normal paediatric eyes  (Fig. 1);
2. In eyes with retinoblastoma  (Fig. 2).
3. In pseudophakic eyes after phacoemulsification with different IOL designs

All photographs were taken with medium to large pupil diameters, frequently immediately after cataract surgery while mydriasis was still present [1].

The following photos show clearly different light reflexes of the peripheral illumination system on the retinal surface.

A very strong ring-shaped reflex can be seen, which includes the macula, optic disc and parts of the near middle periphery.

However, in this example of the Alcon IOL with a stronger posterior curvature, the ring shaped lightreflex is smaller than in other IOLs that produced by a purely biconvex optic.

The next photo shows a very widespread light reflex with a different type of lens. Incidentally, all IOLs were IOLs with a diameter of 6 mm. The effective optic here was approximately 5.8mm.

The following two examples of retinal photographs of a patient with pseudophakia with a different IOL implant (biconvex silicone IOL) show an extremely strong reflex, which also makes it difficult to recognize details of the retina.

Where the strong ring-like reflections come from, whether from the edge of the lens or from of the optics, may be able to show the following photo, taken with a slightly decentered cameraoptic , tilted in order to better recognize details of the peripheral retina.

Visible here is the small circular light reflex probably caused by the optics but also a second one wider light reflex further peripherally, obviously also caused by the lens edge.

Clinical experience showed that a number of patients complained of ring-like reflexes who received IOLs of only 5.0 mm, at that time certainly in order to be able to implant the IOL through a smaller incision, as surgery-related astigmatism was still a problem at that time.

(D Klaas-Stephen Brint AAO 1994 - Alcon Speaker Forum)

Clinical observations during retinal laser surgery

Personal experience with argon laser photocoagulation for retinal breaks in pseodophacic eyes using the Goldmann three-mirror contact lens was reviewed. The laser spot was well focused as usual centrally up to about 50° (e.g. in diabetic retinopathy), but became increasingly astigmatically elongated and distorted towards the periphery. In some cases, cryocoagulation had to be used instead [1].

Anterior-segment OCT

Anterior-segment OCT images (Heidelberg Instruments) were used to compare the anatomy of the natural crystalline lens with that of a pseudophakic eye (Fig. 7) to show clearly the differences of the anatomical design between both optics, the natural and the artificial one.

New OCT photos of the anterior segment of the eye clearly show once again the major difference in anatomy
between :  (Courtesy Heidelberg Instruments)

IOL design concept

A new IOL design was developed in collaboration with Acritec Inc.

(Dr Greiner et al, Munich) in 1993/94. The optic diameter was adapted to the axial length of the eye, following the principle that a larger eye requires larger optics [1]:

Table 1. Diameter adaptation of the IOL according to refractive power (author's design, 1993/94).

Refractive power (D) IOL diameter (mm)

8 – 15 7.5

15.5 – 21.0 7.0

21.5 – 25.0 6.5

25.5 – 30.0 6.0

All IOLs had an aspherical optical design, usually applied to the posterior surface for manufacturing reasons, and from 22 D onwards to both surfaces. 

Here is a Retcam photo of an optic with a diameter of 7.0 mm, aspheric optic design and stronger posterior curvature. You can see a much smaller ring reflex here in the Retcam photo, and not only the central but also the peripheral image quality is much better.

Of course, all photos were taken with medium to large pupil diameters, often - as mydriasis was present - immediately at the end of the cararact surgery. In the following photos you can clearly see the design of this IOL with 6.5 mm diameter immediately before implantation. The reason for the new design was of course to reproduce the surface shape of our natural lens, i.e. a quarter of the refractive power anteriorly and approx. three quarters posteriorly. Of course, these IOLs do not have the thickness of a natural lens. But it is possible
that in the future such posteriorly more convex IOLs could compensate for a decompensation of the vitreous volume.

This photo show the IOL in the slit lamp view postoperatively with greater convexity.

(D Klaas : paper with video examples presented at ESCRS 1993 Amsterdam)

Literature review

Recent studies on aspheric, EDOF, multifocal and accommodating IOLs were reviewed, including the ESCRS 2021 presentations on the ArtIOL (Artal et al.) [2], the AAO 2019 Innovative Forum on accommodating optics (Beer et al.) [3], and analyses of dualoptic accommodating IOLs (Tomas-Juan et al.) [4]. Importantly, none of these patients reported discomfort in the mesopic range, and no reflexes were perceived with laterally incident light in the quality-of-life questions [1]. G. Auffahrt et al (7) examined pseudophakic patients for glare and contrast sensitivity. In summary every second patient >60 yrs. with (bilateral) pseudophakia can be expected to have reduced contrast and glare sensitivity. 0.75% lost their driver license and similar results in Klaas’s presentation to compare over 400 Si- and Acrylic- IOLs (9) New lens designs by Dr Pablo Artal from a US manufacturer recently showed an IOL with improved night vision properties, which also takes more account of mesopic vision through the new design of the peripheral.

IOL components: Compared to traditional intraocular lenses (IOLs), this specific lens design offers measurable functional benefits that enhance safety when driving at night. (P. Artal et al)(2) "ArtIOLs mimic the optics of the natural crystalline lens providing optimized field curvature and peripheral astigmatism leading to an improved peripheral vision" ESCRS 2021, Amsterdam (Accommodative and modular IOL concepts Recent developments in accommodating IOLs (AIOLs) aim to mimic the natural focusing ability of the crystalline lens [2–4]).

Results

Peripheral image quality and ring-shaped reflexes

Retcam imaging of normal paediatric eyes provided reflex-free fundus images up to approximately 160° (Fig. 1). In contrast, Retcam photographs of pseudophakic eyes revealed pronounced ring-shaped light reflexes originating from the peripheral illumination system, overlapping the macula, optic disc and parts of the mid-periphery [1].

The size and intensity of these reflexes differed markedly between IOL designs:

• In eyes with an Alcon IOL with a stronger posterior curvature, the ring-shaped reflex was smaller and the central and peripheral image quality was better (Fig. 3).
• In eyes with a purely biconvex optic (effective optic ≈ 5.8 mm), the light reflex was much more widespread, obscuring larger areas of the retina (Fig. 4).
• Biconvex silicone IOLs produced an extremely strong reflex that made it difficult to recognise retinal details (Fig. 5a, b).
• With a slightly decentred and tilted camera optic, two separate reflexes became visible: a smaller circular reflex probably caused by the optic, and a wider peripheral reflex caused by the lens edge (Fig. 6).

Clinically, a number of patients who had received IOLs with an optic diameter of only 5.0 mm – implanted at that time to allow smaller incisions and reduce surgery-related astigmatism – complained of ring-like reflexes [1].

Anatomical comparison: natural lens versus pseudophakia

Anterior-segment OCT clearly demonstrated the major anatomical difference between the natural crystalline lens and a pseudophakic eye (Fig. 7):

• The natural lens shows an asymmetric, biconvex profile with different anterior and posterior curvatures and a substantial thickness.
• The pseudophakic IOL is thin, symmetric and located in the capsular bag, with a clearly different posterior curvature and distance to the retina.

Diameter-adapted, posteriorly more convex IOL design

Based on these observations, a new IOL design was developed in 1993/94 in collaboration with Acritec Inc. (Dr Greiner Munich) [1]. Key features:

• Optic diameter adapted to axial length (Table 1): 7.5 mm for 8–15 D, 7.0 mm for 15.5–21.0 D, 6.5 mm for 21.5–25.0 D, and 6.0 mm for 25.5–30.0 D.
• Aspherical optical design, usually on the posterior surface, and from 22 D onwards on both surfaces.
• Stronger posterior curvature, aiming to reproduce the natural distribution of refractive power (≈ ¼ anterior, ¾ posterior).

Retcam imaging of an IOL with a 7.0 mm optic, aspheric design and stronger posterior curvature showed a much smaller ring reflex and markedly better central and peripheral image quality (Fig. 8). Photographs taken immediately before implantation illustrate the design of the 6.5 mm IOL (Fig. 9a, b), and the slit-lamp view postoperatively confirms the greater posterior convexity (Fig. 10).

Importantly, none of these patients reported discomfort in the mesopic range, and no reflexes were perceived with laterally incident light in the quality-of-life questions [1].

Accommodative and modular IOL concepts

Recent developments in accommodating IOLs (AIOLs) aim to mimic the natural focusing ability of the crystalline lens [2–4].

Dual-optic accommodating IOLs (e.g. LIBERTY) show greater axial displacement within the capsular bag than single-optic systems, and provide greater accommodative capacity, better optical quality and higher patient satisfaction. However, near vision remains limited, and additional reading glasses are often required [4].

General disadvantages of accommodative systems include:

• limited function with over- or under-correction and unpredictable required power;
• decreasing function over time due to fibrosis and shrinkage of the lens capsule;
• posterior and anterior capsular opacification (PCO/ACO), which remains a central unsolved problem [1,4].
• Artificial capsular bag concepts: The author described and patented an artificial capsular bag with an accommodating device in the 1990s (DE 43 40 205 C1; DE 40 38 088 C2; US 5,52,891) [1]. The concept aims to:
• preserve and stabilise the natural lens capsule;
• restore the distance between the posterior pole of the capsule and the retina;
• allow implantation of a foldable, exchangeable and movable IOL;
• optionally use a photovoltaic coating for controlling servomotors via nanotechnology (TH Karlsruhe).

The Gemini implant (Omega Ophthalmics, Dr. Gary Wörtz; first implantation by Dr. Uday Devgan, LA) corresponds to this principle and represents a modular, exchangeable optic within an artificial capsular bag (Fig. 13) [1].

Figures 11 and 12 show 3D animations of the implantation principle of the artificial capsular bag and the modular stepped model. Figure 14 illustrates a monooptic system with accommodating optics, including Nd:YAG laser relaxing incisions of the anterior capsule to maintain mobility of the optic [3].

Control systems for IOL performance

To monitor IOL performance, artificial eye models were developed early on to measure imaging quality, particularly resolution. Such systems were used, for example, at the Eye Clinic under Prof. Kohnen (Frankfurt) [1].

The author recommends the Retcam as an additional control system, particularly to test reflex behaviour, stray light effects and photographic image quality [1].

Discussion

The present observations support the hypothesis that the geometry of current symmetric, biconvex IOLs with a 6.0 mm optic is a major contributor to peripheral optical limitations, glare and ring-shaped reflexes. The natural crystalline lens is characterised by an asymmetric curvature and a larger effective optical zone, which cannot be reproduced by a thin, symmetric IOL [1].

The findings from Retcam imaging are consistent with clinical experience during retinal laser surgery, where the laser spot became increasingly distorted towards the periphery. This suggests that peripheral optical quality is systematically underestimated in current IOL design and clinical testing.

The diameter-adapted, posteriorly more convex and aspheric IOL design described here represents an early attempt at individualised optical rehabilitation. The principle – adapting the optic diameter to the axial length of the eye – anticipates later developments such as the ArtIOL, which mimics the optics of the natural crystalline lens and has been shown to provide optimised field curvature, reduced peripheral astigmatism and better peripheral contrast sensitivity in pseudophakic patients [2].

Several limitations must be acknowledged:

• The observations are largely personal, observational and photographic, not controlled clinical trials.
• The number of patients and the follow-up data are limited.
• The Retcam is primarily a paediatric imaging device; its use in pseudophakic adults is off-label and not standardised.

Nevertheless, the consistency between photographic findings, clinical experience, OCT anatomy and published studies supports the validity of the underlying concept.

Future directions include:

1. Asymmetric, posteriorly more convex IOL designs with larger effective optical zones.
2. Modular and exchangeable optic systems within an artificial capsular bag, allowing adjustment for refractive changes or future technologies [1].
3. Dual-optic accommodating IOLs, which show greater axial displacement and better accommodative capacity, but still require improvement in near vision, long-term stability and PCO prevention [4].
4. Pharmacological approaches such as eye drops based on the pinhole effect, which have shown considerable improvement in presbyopia in pseudophakic eyes [1].
5. Standardised peripheral optical testing using wide-field imaging systems such as the Retcam.

Summary / Conclusion

Accommodating IOLs with dual optics exhibit greater axial displacement within the capsular bag than accommodating IOLs with a single optic [4]. However, further studies are needed to confirm this major shift.

The dual-optic accommodating IOL also offers greater accommodative capacity, better optical quality and higher patient satisfaction. Nevertheless, results at close range are still limited, and additional reading glasses are often required [4]. In addition, the formation of posterior and anterior capsular opacification could possibly be reduced by special design and new materials, contributing to better long-term function.

Accommodative intraocular lenses (AIOLs) are designed to mimic the natural focusing ability of the crystalline lens. In contrast to conventional monofocal IOLs, which provide clear vision at only one distance, AIOLs can adjust their shape and position within the eye to provide clear vision at multiple distances [2–4].

The development of AIOLs has been an active area of research:

• One of the first designs was developed in the 1960s, using a spring-like mechanism to change the shape of the lens. These early designs were unsuccessful due to problems with stability and long-term effectiveness [4].
• 
  In the 1990s, a new generation of AIOLs used hinged plates or segments that move within the lens to change shape and adjust focus. This design has been more successful, and several types are now available on the market [4].

A central challenge has been to ensure long-term stability and effectiveness without compromising image quality or causing unwanted side effects [4]. Despite these challenges, development continues, and AIOLs are likely to become more effective in the treatment of age-related vision loss and other diseases that impair the natural focusing ability of the eye.

A possible pioneering step in the right direction is a movable lens within an artificial capsular bag (e.g. the Gemini artificial capsular bag, developed by Omega Ophthalmics and Dr. Gary Wörtz), (Fig11)  a principle first described and patented by the author in 1990 [1]

(D Klaas: 1993/95 intraocular lens with an accommodating device DE 43 40 205 C121990/94 artificial capsular bag, photovoltaric layer) + (DE 40 38 088 C22 USA Patent No. 5,52,891 / 1996 Intraocular Lens Accomodating Device)

This could then also be given a corresponding so-called base refractive force even allow much better peripheral vision due to the special size of the optics.

A second lens would then be attached to this.

Some photos from our own 3D animations show the basic principle ofimplanting the artificial capsular bag to stabilize the shape of the capsular bag.

Finally, the author states his personal preference: if an IOL implantation were necessary, he would choose a mix-and-match strategy:

• Leading eye: unrestricted distance acuity with a maximum residual refraction of –0.5 D.
• Fellow eye: monofocal IOL with slight myopia of approximately –1.25 to –1.75 D.

This strategy might achieve excellent sharpness with better depth of field and better contrast vision, supporting a good quality of life with extensive independence from spectacles. When choosing an IOL, no compromises should be made in terms of material and image quality [1]. I personally would give the ART-IOL-concept best chances for excellent vision over all and even in low-light circumstances and I would strongly prefer Pablo Artals Ideas and concepts.

Finally to summarize a brief overview of the most important innovations in modern IOL implants:

1. aspheric monofocal lenses (standard today)
2. aspheric monofocal lenses with extended depth of focus
3. aspheric multifocal lenses
4. accommodative lens systems; mono- or dual-optic systems
5. a mono-optic system with accommodating optics (Beer et al, AAO 2019- Innovative Forum) ND Yag laser relaxing incisions in the front capsule to maintain the mobility of the optics within the capsule.
6. Liquid-filled and other so-called dual-optic IOLs "Axial movement of the dual-optic accommodating intraocular lens for  the correction of the presbyopia: Optical performance a