Lens Fluorescence Research Articles

A new method of measuring in vivo the lens transmittance, and study of lens scatter, fluorescence and transmittance.

We propose a new method to measure in vivo nuclear transmittance using scanning photometry, thus complementing its present application in measuring lens scatter and fluorescence. We compared our method of measuring the transmittance with a previously reported in vivo method and found an adequate correlation. We then measured the fluorescence, scatter and transmittance of lenses without cataract and those with as much as a mild yellowing. The three phenomena correlated with age. In addition, this study allowed a correlation of the three phenomena with each other, indicating that the loss of transmittance of the nucleus cannot be explained by its thickening alone but that changes in its composition must take place. Finally, a preliminary study on diabetics showed early onset of the process responsible for the increase in lens fluorescence. This process did not seem to be accelerated in diabetics in comparison with normals. The nuclear scatter appeared to increase more rapidly with age in nondiabetics as compared to diabetics. This preliminary study suggests mainly that scanning photometry can be used to study aging and pathologic changes in the lens.

Laser selected fluorescence of human cataractous lenses at liquid helium temperatures

Laser excitation of an inhomogeneous distribution of chromophors at temperatures near 0 K is known to result in sharp fluorecence spectra in numerous systems. When this technique was applied to human cataractous lenses at 4 K, broad fluorescence resulted. The wavelengths of maximum fluorescence were different from those previously reported, thus demonstrating the observation of new fluorophors. The broad fluorescence appears to result from internal conversion and energy transfer processes and not from low frequency vibrational motions or strong vibronic coupling. Consequently, other site selection techniques, such as spectral hole burning, may produce sharp spectra with vibronic structure that can be used to identify the molecular species involved.

An Experimental and Clinical Evaluation of Lens Transparency and Aging

The normal human lens is a precisely formed structure containing about 65% water and 35% organic matter, the latter being mainly (greater than 90%) structural proteins. The lens becomes encapsulated at the 13 mm embryonic stage and is consequently divorced from a direct blood supply for life. It provides the investigator with an organ that exists in an environment analogous to a single-cell type of tissue culture system and can be reproduced in vitro. Since the cornea and lens are transparent one can directly monitor morphologic and biochemical aging changes in vivo. Recent developments now permit us to monitor certain molecular changes as well. Thus this organ can serve as a unique model for studying in vivo aging parameters. In vivo UV slit lamp densitography to monitor lens fluorescence provides us with a useful diagnostic and prognostic screening method to identify lens photodamage due to excess UV exposure (occupational or accidental), photosensitizers (e.g. psoralens) as well as the normal age related increase in lenticular fluorescence. Cortical opacities are also a common finding in older individuals. In vitro NMR (human and animal lenses) and in vivo (animal experiments) currently in progress are rapidly elucidating the physicochemical basis for the development of light scattering areas in the aging lens cortex. This review demonstrates the feasibility of utilizing biophysical methods, in particular, optical spectroscopy and NMR analyses to delineate and monitor specific age related parameters in the ocular lens, in vivo as well as in vitro.

Ocular Phototoxicity and Psoralen Plus Ultraviolet Radiation (320–400 nm) Therapy: An Experimental and Clinical Evaluation<xref ref-type="fn" rid="FN1">1</xref><xref ref-type="fn" rid="FN2">2</xref><xref ref-type="fn" rid="FN3">3</xref>

The increase in fluorescent chromophores within the human ocular lens is age related, leading to an increasingly yellow core (nucleus) that presumably results from UV radiation exposure. In approximately 10% of our population this process progresses more rapidly, resulting in the formation of the brown (nuclear) cataract. Some lenticular discoloration may be beneficial, since it enables the mature lens to filter UV and short-wavelength visible radiation, thus protecting the retina from potential photodamage. Aphakic primate retinas can be irreversibly damaged by exposure to approximately 5 mW.cm-2 long-wavelength UV (greater than 325 nm) radiation. Photosensitized damage to the lens and retina with psoralen plus UV radiation (320-400 nm) (PUVA) has been demonstrated in experimental animals, and cataracts have recently been reported in patients given PUVA therapy. A new method to screen patients for lens damage is by enhanced fluorescence measurements. This method, UV slit-lamp densitography, permits detection of lenticular photodamage at a molecular level, years before visible opacities become manifest by conventional slit-lamp examination. This procedure has also demonstrated a significantly lower level of lens fluorescence (hence decreased filtering capacity) in patients with retinal degenerative diseases, suggesting UV photodamage as a factor in the progression and perhaps pathogenesis of these conditions.

Ultraviolet-visible slit lamp densitography of the human eye

A new slit lamp densitographic apparatus (based on the Scheimpflug principle) capable of accurately and reproducibly recording visible changes in lens density as it ages was recently introduced. We have modified this apparatus to utilize u.v. radiation (300–400 nm) to measure and quantitate the age related fluorescence levels in the normal lens in vivo and correlate them with our in vitro data reported in previous communications. These studies demonstrate the feasibility of obtaining in vivo lens fluorescence data which are objective, reproducible and can be quantified. Several laboratories have demonstrated that u.v. radiation (longer than 300 nm) can play a role in the generation and enhancement of non-tryptophan fluorescence of lens proteins. Furthermore, we have previously reported that 8-methoxypsoralen, a known u.v. photosensitizer (used in treating psoriasis) can become photobound to nucleic acids and proteins within the lens resulting in its accumulation and the enhancement of lenticular fluoresence and phosphorescence. Thus, u.v. slit lamp densitography can be used to monitor objectively one parameter of lens aging (fluorescence) as well as photosensitized lens damage at a molecular level years before visible opacities become manifest by conventional slit lamp examination.

In vivo Lens Fluorescence Photography

We are reporting a new, objective and quantitative method for monitoring age-related molecular changes in the human ocular lens in vivo, as expressed by increases in at least two (nontryptophan) fluorescence wavelengths. These data correlate with previously reported in vitro lens fluorescence changes which are associated with the aging process. This method will also detect alterations in lenticular fluorescence caused by photosensitized as well as direct ultraviolet radiation damage.

Photoacoustic, Fluorescence and Light Transmission Spectra of Normal, Aging and Cataractous Lenses

Photoacoustic spectroscopy (PAS) reveals the presence of a 340–360 nm absorption band in the normal lens which increases in magnitude with age and is particularly pronounced in the brown nuclear cataract. The cortical cataracts showed low fluorescence and PAS absorption while the mixed cataracts showed intermediate levels of fluorescence intensity and PAS absorption. These data provide further evidence that the age-related accumulation of fluorescent pigments is responsible for the increasing yellow color of the lens nucleus and the corresponding decrease in UV and visible transmission. The brown nuclear cataract appears to be an extreme example of such a process. The development of anterior cortical opacification prevents further photochemical generation of the fluorescent pigments and the corresponding PAS absorption band.

Fluorescence in human lens

In human lens there are two major types of fluorescence, one of which is emitted around 340 nm when excited at 290 nm (purple fluorescence), and the other with activation and emission wavelength respectively in the neighborhood of 340 and 420 nm (blue fluorescence). The level of the purple fluorescence is high in comparison with that of the blue in all the protein fractions of the lens examined. In both fluorescence, urea soluble (U.S.) fraction of the insuluble protein shows the highest level, and gamma crystallin the lowest, whereas the level in alpha and beta crystallins is in between. The purple fluorescence of the human lens associated with both soluble and insoluble fraction seems to be maintained at a relatively constant level throughout life of human lens, while the blue fluorescence observed in both soluble and insoluble fractions increases with age. The age-related changes in the blue fluorescence is more conspicuous in the U.S. fraction than in the soluble proteins. It appears that the increase in lens fluorescence observed with age is attributed mainly to the blue fluorescence.

Tryptophan excited states and cataracts in the human lens.

WE present here a study of the fluorescence and phosphorescence of human eye lenses in vitro with regard to the mechanisms of formation of cataracts. Light transmission by the cornea decreases rapidly with decreasing wavelength, and is essentially zero for wavelengths less than 293 nm1–3. The important effect of this corneal absorption was demonstrated by Bachem3 who induced cataracts in guinea-pigs and rabbits with ultraviolet light and presented an action spectrum to show that the efficiency of in vivo cataract production rose steeply, from zero at 293 nm to maximum at 300 nm, and then fell off sharply at 313 nm with a long tail extending to about 365 nm. This action spectrum and the corneal absorption spectrum are shown in Fig. 1.

The Problem of Fluorescence of Human Cataractous Lenses

Total fluorescence intensity of human lens extracts increases with degree of lens opacities. This fluorescence increase is not due to an increase of the phosphorylated pteridine like substance (PLS).

The fluorescence of the serum in rats with alloxan diabetes and cataract. I. Intensity determinations.

Summary.The theory has been presented that fluorescing compounds are deposited in the lens at the formation of an experimental diabetic cataract. The increase of the lens fluorescence was previously stated. A marked and significant increase of the serum fluorescence has been recorded in rats with alloxan diabetes, complicated by cataracts. No change of the fluorescence intensity could be observed in other experimental groups comprising diabetes with clear lenses and alloxan treatment, not giving rise to diabetes. Special regard was paid to hemolysis, different emptied blood deph, pH and absorption in different spectral regions of the serum samples. but the influence of these factors did not constitute any appreciable source of error.