Development of a Scheimpflug imaging equipped OCT system to measure gradient refractive index of the lens in the human eye in vivo

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Project Summary/Abstract The crystalline lens of the human eye grows throughout life with continuous change in its size, shape and internal structure. The lifetime growth of the lens generates a special structure inside the lens: the gradient distribution. From the lens surface to the lens center, the gradient distribution is characterized in its fiber cell concentration, water content and protein concentration at the cellular level. Meanwhile, a cellular mechanism is also established inside the lens to maintain the gradient structure and health of the lens. At the functional level, the gradient cellular structure produces a gradient refractive index (GRIN) of the lens. The lens GRIN causes negative spherical aberration and improves optical quality of the eye by compensating positive spherical aberration from the cornea in both relaxed and accommodated eyes. Better understanding of the lens GRIN is important for eye care professionals in the areas of refractive and cataract surgeries to optimize their surgery design and for vision scientists to explore the cellular mechanisms underlying the developments of presbyopia and cataract. However, accessing the lens GRIN in the human eye in vivo has been a challenge to vision researchers for more than a century. Recently, the Principal Investigator (PI) discovered a novel principle to approach this difficult task by combining Scheimpflug imaging (SI) with anterior segment optical coherence tomography (AS-OCT). This proposed project aims to develop a novel ray-tracing SI equipped AS-OCT system to measure the lens GRIN of the human eye in vivo by applying breakthroughs the PI has recently achieved including: (1) discovery of the principle of in vivo measurement of radial lens GRIN by using a combination of a ray-tracing SI and AS-OCT imaging; (2) discovery of the ray-tracing SI method to identify the point at the posterior lens surface from where the measured lights for both SI and AS-OCT systems were reflected. Advantages of the new system include: (1) constructing a ray-tracing SI equipped AS-OCT system which provides a unique instrument to image the anterior segment of the eye and to study the morphological and optical properties of the lens in vivo; (2) for the first time, accurately measuring radial lens GRIN of the human eye in vivo without any assumption about the optical property of the lens; (3) for the first time, accurately assessing radial lens thickness of the human eye in vivo; (4) accurately deriving profiles of the posterior lens surface of the human eye in vivo; and (5) estimating abnormalities of the refractive index in the aging eye or the eye with cataract development in vivo. Successful accomplishment of the goals of this project will eventually allow us to better understand the functional role of the lens GRIN and its underlying cellular mechanisms in normal and defective eyes and potentially to find effective interventions to control presbyopia and cataract development. It will also present a substantial breakthrough in the methodology for diagnosing lens aging in daily eye care and for revolutionizing refractive and accommodation-restoring surgeries in current clinical practice.