Abstract:
The focus shift from far to near, called accommodation, is controlled by a contraction of the ciliary muscle, leading to a change in the curvature of the crystalline lens. This con-traction leads to changes in electrical potentials, which are recorded as neuromuscular biosignals. While the ciliary muscle stays functional throughout life, the crystalline lens gets stiffer, leading to a decline in the ability to change its shape and to focus on near objects. This condition, called “Presbyopia”, starts during the mid-forties and progresses with age. Current vision treatments, like progressive lenses, contact lenses, and intraocu-lar lenses, as well as pharmaceutical treatments, have their merits and limitations, but none of them restore natural accommodation. To this day, the subjective amplitude of accommodation (AoA) is used not only to monitor the progress of presbyopia and help opticians assess subjective visual perception, but also in ongoing research investigating the related accommodative-biopotentials. Even though the limitations of subjective meas-urement methods to determine the AoA are known, they are still applied in daily clinical practice because of their ease and speed of the procedure. Within the scope of the work “Comparing a Novel Motorized Push-Up Ruler with Conventional Subjective Methods for Measuring the Amplitude of Accommodation”, an improved, motorized push-up ruler was developed and compared against the clinical standards push-up and push-down meth-ods. Additionally, the volunteers were asked about their satisfaction with the ease of use, and their confidence in the measurement reliability. The findings showed that the motor-ized version was superior in reliability without compromising precision, reducing known examiner limitations of the standard subjective procedures. Besides that, the subjective impression showed that the participants were more convinced by the motorized push-up ruler. Therefore, the motorized ruler was utilized in the contact lens electrode study “Non-invasive measuring of biopotentials of the ciliary muscle during accommodation in em-metropes” in 12 participants, in which the biopotentials of the ciliary muscle during ac-commodation were characterized. Even though accommodation-related biopotentials and artifacts characteristics are essential for the adaptive control of an artificial lens in the future, previous studies have only demonstrated their presence without providing a de-tailed characterization of these signals and artifacts. By comparing these biopotentials with refractive measurements using eccentric infrared photorefraction during a controlled change in focus, it was possible to characterize accommodation-related biopotentials and
related artifacts such as blinking or eye movements. An intraocular measurement of the signals, taken directly at the origin, is expected to be less influenced by artifacts. For this reason, a novel approach to detecting ciliary muscle biopotentials is to use a ring electrode implant. In the manuscript “Design and In Vivo Evaluation of an Intraocular Electrode for Ciliary Muscle Biopotential Measurement in a Non-Human Primate Model of Human Accommodation” the consecutive steps from the conception phase towards testing, first in a simulated, and subsequently in an in vivo model are presented. The manufacturing included femto-laser cutting and physical vapor coating. The long-term stability was as-sessed via accelerated aging at 60°C in phosphate-buffered saline solution together with an electrical impedance measurement to detect possible electrical shifts over time. This is the first work measuring biopotentials of the ciliary muscle via a wireless intraocular implant.
The ring electrode implant and the contact lens electrode pave the way towards new pres-byopia treatments. They enable the control of tunable lenses and thereby restore natural accommodation through neuromuscular signals of the ciliary muscle, as indicated by the preliminary results of the study “Preserved Ciliary Muscle Biopotentials Enable Artificial Lens Control and Near Vision Recovery in Long-Term Presbyopia”. In parallel, the mo-torized AoA measurement helps to improve the study and clinical quality of subjective measurement methods. Overall, this work enhances our understanding of accommodation by focusing on the electrical biopotentials of the ciliary muscle, which have been poorly investigated to date. The findings hold promising potential for the development of new visual aids that enable more natural focusing.
presbyopia