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Modelling reveals mysteries of accommodation

Sydney, Australia, 24 April 2015: The mysteries of accommodation are being revealed by advanced modelling and revolutionary imaging systems, suggesting a breakthrough synthetic lens to replace the presbyopic crystalline lens and restore accommodation is a not too distant prospect.

Researchers from Brien Holden Vision Institute and Bascom Palmer Eye Institute (BPEI), the number one ophthalmology centre in the US, have been collaborating through the Vision Cooperative Research Centre to find a ‘treatment’ for presbyopia since the 1990s.

“One of the keys to the success of the project, which is developing a synthetic polymer gel to replace the natural contents of the aged crystalline lens of the presbyopic eye, is a complete understanding of the properties of the natural lens and accommodation system,” says Dr Hooman Pour, Research Fellow at Brien Holden Vision Institute.

Dr Pour is seeking to help determine the necessary homogeneous mechanical and optical properties of a replacement gel that will yield the required optical response of the natural lens. “This process is made complex by the interplay between the mechanical and optical gradients,” says Dr Pour, who presented the research at the recent Ophthalmic Technologies conference of the annual SPIE Photonics West meeting, the world’s leading laser, photonics, and biomedical optics meeting.

“The refractive index is not uniformly distributed throughout the lens, meaning its ability to refract light changes as you move across or through it. Coupled with this are the mechanical stiffness changes throughout the lens that govern the lens change in shape when switching between ‘distant’ and ‘near’ vision. We need to both quantify the refractive index and stiffness changes across the lens and also understand the interplay between the mechanical and optical properties in order to replicate this in a synthetic lens.

 

THE LATEST MECHANICALLY AND OPTICALLY GRADIENT MODEL OF THE HUMAN ACCOMMODATION SYSTEM

“Using techniques such as numerical ray-tracing and finite element method, has enabled us to test the effect of varying the isotropic, or uniform, elasticity and refractive index on the accommodative response of the lens. In particular we wanted to test the effects on accommodative amplitude, which we found is a function of the refractive index and modulus of elasticity.

“The results will inform the ongoing work of our chemists, who are testing different polymer compositions to produce a product that will mimic the response of the natural lens.”

The BPEI researchers have developed an imaging system that for the first time is able to visualise all of the key elements of the accommodation system – the crystalline lens, the ciliary muscle, and the zonular fibres. The revolutionary four-dimensional instrument was conceived to quantify the mechanism of accommodation in real time, says Professor Jean-Marie Parel, Director of the Ophthalmic Biophysics Center at BPEI.

“It dynamically shows and records cross-sections of the whole eye, hence monitoring the intraocular structural changes in the lens and ciliary muscle that occur when the subject accommodates and disaccommodates,” Professor Parel says.

“It was designed to objectively assess the changes that occur in young and presbyopic subjects and the efficacy of implants designed to restore accommodation.”

This research was presented at the Ophthalmic Technologies conference, a part of SPIE (international society for optics and photonics) Photonics West meeting in San Francisco recently.