טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAzzam Naiel
SubjectUV-A Damage to the Eye Lens in Organ Culture
DepartmentDepartment of Medicine
Supervisor Dr. Ahuva Dovrat


Abstract

The research investigates the effects of UV-A radiation on the eye lens. The role of the lens is to focus light on the retina, consequently, the lens must remain transparent throughout life. If a lens becomes opaque the visual processes are impaired.

UV-A is a component of sunlight which is absorbed mostly by the lens. Consequently, this radiation is the main source of radiation that causes damage to the ocular lens. Aims of the study: (1)  To determine the threshold of UV-A irradiation from which the lens can still recover fully. (2) To reveal whether UV-A damage has a cumulative effect. (3) To investigate the morphology of UV-A damage on lenses studied by scanning electron microscopy (SEM). Bovine lenses were excised from eyes and placed in a specially designed chamber for organ culture. The chamber was filled with appropriate culture medium, surrounding the lens. Optical quality of the lenses was determined daily using an automated scanning laser system. The irradiation treatment was carried out 24 hours after incubation. Irradiation with 31 J/cm2 showed optical damage to the lenses, which did not have the ability to recover during the culture period. Irradiation with 29 J/cm2 caused no optical damage to young (up to 1 year old) lenses. On the contrary, old (4-8 years old) lenses showed increasing damage, but full recovery by the last day of culture. The enzymatic activities of 4 enzymes (Catalase, G-6-PD, Aldolase, Na-K-ATPase) in the lens were measured. All enzymes recovered fully throughout the culture period in both age groups. Analysis of lens crystallins by SDS gel electrophoresis showed no changes in the profile of lens structural proteins. We conclude that the threshold of UV-A irradiation at which the lens can recover fully from damage is 29 J/cm2.

In order to determine whether the UV-A damage has a cumulative effect, young lenses were exposed to a damaging irradiation in two different ways: (1) Irradiation with 33 J/cm2 in one day. (2) Irradiation with 33 J/cm2, in 4 steps of 8.25 J/cm2 each, once in 24 hours. Lenses irradiated over 4 days showed optical and biochemical damage that was greater than in the   one-day irradiated lenses, without any ability for repair, even partially. We conclude that the UV-A damage has a cumulative effect. Scanning electron microscopy (SEM) analysis indicated structural injury to fiber cells caused by UV-A radiation.