Photobleaching of a 58 year old human donor lens was demonstrated using an infra-red, femtosecond Ti:Sapphire laser. Pulse duration was 300 femtoseconds, pulse energy was 0.1 μJ, and the focal spotsize of the laser was approximately 14 μm in diameter. The lens was treated in a 1x1 mm large area by scanning the laser beam. Significant photobleaching was seen after laser treatment. Light transmission increased by 7%. The greatest effect was seen in the blue-green part of the visible spectrum.
The transmission properties of the human lens were studied in donor lenses from the age of 17 to 76 years. The
transmission of white light was measured using a fiber coupled tungsten halogen lamp. The light transmitted by the lens
was collected using an integrating sphere that was coupled to a spectrometer by an optical fiber. As expected, the
transmission of blue and green light decreased in older lenses. The transmission of the near infrared part of the spectrum
was above 90% even in old donor lenses.
Ultrafast femtosecond lasers are used increasingly for a wide range of medical purposes. The immediate tissue response
to pulses above a certain threshold is optically or laser induced breakdown, which is often visible as gas-filled cavities
that persist for some time. In the present study, we attempted to define the cavitation threshold in the human lens in vitro
using multiphoton effects based on radiation from a femtosecond 800 nm Ti:Sapphire laser. Cavitations were observed
from pulse energy densities exceeding 16 mJ/cm<sup>2</sup>, but only after several minutes of exposure and not as a result of a
single laser pulse. This suggests that cavitations were caused by a process which differs from the single-pulse cavitations
observed at higher intensities. To evaluate whether the release of gas was caused by ionization and plasma formation or
by thermal effects, we introduced pauses into the pulse train, which did not change the total exposure time needed to
form a cavitation. This suggests that local heating did not play a significant role in producing the observed phenomenon,
suggesting that photochemical reactions may be involved. These results demonstrate that there are several types of
ultrafast laser effects in the lens that have a potential for therapeutic application and treatment of eye disease though
further studies are needed to shed light on the nature of the formation of delayed cavitations.
Type 2 diabetes mellitus is a global epidemic with the number of affected subjects exceeding 4% of the adult population world-wide. Undiagnosed and untreated, the disease results in long-term complications such as myocardial infarction, stroke, and blindness. Treatment reduces the number and severity of long-term complications but treatment is often delayed by a time-lag of 10 years or more from the onset of disease to diagnosis. Earlier diagnosis can be achieved by systematic screening programs but the potential time won is unknown. The aim of the present study was to develop a mathematical model estimating the prediagnostic duration of type 2 diabetes mellitus using lens autofluorescence as an indicator of lifetime glycemic load. Fluorometry of the human is lens a quantitative measurement which is attractive because of the ease by which it can be performed. It is our hope that lens fluorometry will prove useful in estimating the prediagnostic duration of type 2 diabetes mellitus in population studies, a property of profound clinical relevance that is difficult to estimate by any other currently available method.