Otto Hockwin

An Index for Human Lens Transparency Related to Age and Lens Layer: Comparison between Normal Volunteers and Diabetic Patients with Still Clear Lenses

Objective: The light scattering intensity of normal, clear lenses varies with age and with the localization within the lens. Realizing the biometry of single lens areas together with their relevant light scattering intensity one should be able to calculate an index to express the lens transparency properties of normal human lenses in dependence on age. Performing the same procedure in cases of diabetic patients with still clear lenses it should become possible to obtain an index for the lens transparency properties of lenses under the ‘risk factor’ diabetes. Methods: 748 eyes with transparent lenses in 383 healthy individuals and 134 eyes with clear lenses in 70 subjects with diabetes were examined. Scheimpflug slit images of the lens were documented by a Nidek EAS-1000 instrument. Biometry for measuring the distance of the single lens layers from the anterior capsule and densitometry for determining the light scattering intensity of six defined lens layers along the (theoretical) optical axis were performed. The index of the lens transparency properties was calculated using the light scattering intensity of a defined lens layer and its distance from the anterior capsule. Results: Lens thickness and light scattering intensities increased linearly with increasing age in the normal population as well as in the diabetic patients. The densitogram pattern of the light scattering intensities in the defined representative six points was similar in both populations, but in the diabetic group the lens thickness was larger and the light scattering intensities were higher at all ages. Conclusion: The index of lens transparency properties calculated with the light scattering intensities of a certain lens area and its distance from the anterior capsule is a useful measure of lens clarity in dependence on age. ‘Clear’ lenses of the diabetic population show significantly higher indices for the lens transparency properties in all age groups.

Location and severity of UVB irradiation damage in the rat lens

We investigated the location and severity of lens opacities and epithelial alterations following ultraviolet-B (UVB) irradiation in vivo, using Brown Norway rats. A group of 9 rats received 65 mJ/cm2 UVB irradiation from overhead lamps every 6 days. Lens changes were documented and evaluated by an anterior eye segment analysis system. Lens epithelial cells were examined postmortem in flat preparations. After 8 weeks of the irradiation schedule (total dose: 0.6 J/cm2), an anterior polar opacity was apparent; at 16 weeks, the opacities had progressed more deeply into the cortex. At postmortem examination, cells in the central region displayed disorganization, clumping, some pyknotic nuclei and mitosis. There were deeper opacities and cell damage was more severe above the central horizontal plane than below it. This present study demonstrated that UVB damage differed in the superior and inferior parts divided by a horizontal plane through the lens anterior pole, when the UVB source was above and there was no reflection from below or laterally. The lens epithelial cells, and associated lens fibers, are the first target of UVB irradiation.

Evaluation of functional and morphologic parameters of the cornea after epikeratophakia using prelathed, lyophilized tissue.

Up to now, the attention of ophthalmic surgeons has been focused mainly on the clinical results of epikeratophakia, demonstrating its safety, relative predictability, and capability of correcting a wide range of refractive errors. However, no prospective study has ever been undertaken to evaluate the influence of epikeratophakia on various physiologic and morphologic parameters of the cornea. The authors investigated some of these parameters prospectively in eight consecutive patients undergoing epikeratophakia with prelathed, lyophilized tissue. Fluorophotometric evaluation of the epithelial barrier function, corneal densitometry by means of Scheimpflug photography, and endothelial specular microscopy were performed preoperatively and 2, 4, 8, 12, and 24 weeks after epikeratophakia. The epithelial barrier function was shown to return to normal 4 weeks after surgery. The optical density of both the epi-lenses and the host corneas increased early after surgery, but was comparable to that of unoperated corneas 6 weeks postoperatively in all cases but one. The endothelial cell density was not altered by surgery in any patient. Despite the limited number of patients, this study indicates that most functional and morphologic parameters of the cornea are normal as early as 6 weeks after epikeratophakia in most cases.

Evaluating Cataract Development with the Scheimpflug Camera

Documentation of pathologic findings in the lens over a prolonged period is rather difficult. Until recently, only written reports or drawings of the process have been employed. Photography with the slit-lamp microscope has not been effective because of the insufficient depth of field and the poor reproduction capacity of instrumental parameters. Occasionally, opacifications of the lens have been photographed using the retroillumination technique1,2 where the cataracts appear as shaded areas, which may then be evaluated by planimetry. Application of this method to clinical problems, however, has met with difficulties,3–7 which may in part be attributed to problems of image analysis but are mostly due to inadequate reproducibility.8,9

In Vivo Evaluation of Epikeratophakia Lenses By Means of Scheimpflug Photography

The recovery of clarity in frozen, lyophilized human tissue lenticules used for epikeratophakia has been a matter of controversy. According to some authors, several months are necessary for the lenticules to resume normal transparency; others report clinical experience of much shorter times. Up to now, objective documentation of such findings has not been substantiated. We used a Topcon LS-45 camera to photograph four eyes that underwent epikeratophakia, preoperatively and at 2, 4, 6, and 8 weeks after surgery, and analyzed the film negatives by linear microdensitometry. The degree of film blackening, that is the density of the tissue, was expressed graphically by peaks of various height measured in millimeters. Best spectacle corrected Snellen visual acuity was also recorded. Similar measurements of corneal transparency were performed in 20 healthy adult volunteers whose best corrected spectacle visual acuity was 20/20. In the four operated eyes, (two keratoconus, one aphakia, and one myopia), the light scattering was increased in both the host cornea and the donor lenticule. The lenticule had a considerably increased light scattering in all patients at both 2 and 4 weeks after surgery, but was comparable to that of unoperated corneas in three of four patients at 6 weeks.

Determination of AL01576 concentration in rat lenses and plasma by bioassay for aldose reductase activity measurements.

Investigations on the disposition of the highly effective aldose reductase inhibitor AL01576 were carried out in pigmented rats after oral dosing and topical administration of a 0.1% ophthalmic suspension by means of an assay modified from a previously described method measuring aldose reductase activity. The crude enzyme extract of pig lenses was used as a test system. From the activity remaining after addition of the plasma or lens extracts, the concentration could be determined since the inhibition constant (IC50) of AL01576 is known. With this procedure, the concentration of AL01576 in plasma and lenses of Brown-Norway rats given different doses of the drug for 42 consecutive days were determined and compared with a gas chromatographic assay technique. These data indicate that AL01576 is absorbed into the lens with a substantial portion redistributing into the lens following systemic delivery. Drug concentrations were correlated with efficacy measurements, though they were lower in an animal group treated with naphthalene to provoke cataract formation. In a second animal series with Brown-Norway rats over 5 days, AL01576 was administered three times per day to the right eye only. During the washout period, AL01576 had a long persistence in plasma and lenses following this short-term topical ocular administration.

In vitro UV-B effect on lens protein solutions.

To investigate the effects of UV-B exposure on the protein solutions of different lens parts, rabbit lenses were separated into the equator (Eq), anterior cortex (Ac), nucleus (Nu) and posterior cortex (Pc). After homogenization, the water-soluble protein from each part was irradiated with UV-B at 0 to 0.225 J/cm2. Alterations in the content of protein SH, carbonyl groups, light scattering intensity and SDS-PAGE pattern were measured to compare the effect of UV-B on the protein solutions of various lens parts with or without additional GSH to test its preventive effect. The results showed that after UV-B irradiation, the protein sulfhydryl groups are gradually reduced. The nonprotein thiol (GSH added to the protein solution) was lost more rapidly than the protein sulfhydryl. The high molecular bands on the SDS-PAGE pattern mainly aggregated with disulfide. UV-B damage also increased the content of carbonyl groups and light scattering, irrespective of the lens parts. Lens proteins from the equator suffered the least damage while those of the nucleus were most strongly affected by UV-B exposure. This study suggests that the lens proteins from various lens parts have different responses to UV-B exposure; the sensitivity was in the following order: Eq < Ac < or = Pc < Nu.

In vivo morphological changes in rat lenses induced by the administration of prednisolone after subliminal X-irradiation. A preliminary report.

In order to induce steroid cataracts in rat lenses, prednisolone acetate was administered together with a single subliminal dose of X-irradiation, which was applied unilaterally before steroid application started. The rats were divided into a control group (without prednisolone acetate administration), a group with a topically administered daily dose of 1 mg/kg prednisolone acetate suspension and a group with a systemically applied daily dose of 0.8-1.0 mg/kg prednisolone acetate suspension. Changes in the lens were objectively evaluated with in vivo Scheimpflug slit images during a 30-week period. Although body weight increase was significantly affected in both groups administered prednisolone, animals survived until the end of the observation period. The initial changes in the lens were the dissociation of the Y-suture and a slight increase in scattering light intensity at the posterior embryonic nucleus after both topical and systemic steroid administration.

High Hurdle of Clinical Trials to Demonstrate Efficacy of Anticataractogenic Drugs

Recently, the rapid progression of cataract surgical technique has led cataract patients in industrialized countries to ignore the possibilities of drug therapy. Globally, however, it will be impossible in the near future to treat cataract by surgery alone, mainly due to medicoeconomic reasons. Preventative measures must be sought. As one of the these measures, the development of anticataractogenic drugs has reemerged as a focus in the lens research field. Although clinical trials of newly developed drugs are absolutely necessary before they enter the market, they have been considered to be a rather easy task. However, in order to gain accurate and reproducible data from trials, the trial program must be carefully prepared. The numbers of participants to the trial, the selection criteria of the subjects, the objective judgment of cataractous changes, follow-up period, a high technical level for cataract documentation and image analysis are proposed. Although there still remain some difficulties concerning the methods for objective judgment, a scientifically acceptable examination must be conducted.