Light scattering in donor lenses.

Light scattering for normal and cataractous lenses from 21-86 yr old donors was measured in vitro. As expected, scattering increased with severity of cataract. Scattering decreased with angle according to a power law. This corresponded to the power law finding for functional straylight measurements in early-cataract patients using white light (power around -2). In vitro, straylight increased monotonically from 700 nm (power around -2.3) towards 400 nm (power around -2.0). For extreme cataracts the angular dependence flattened at small angles. The present results suggest that the structures dominating in light scattering differ not by scattering type but by number, and that they are not very small compared to wavelength. The present results were used to specify the separate effects of light absorption and light scattering on lenticular light transmission.

Quantitative analysis of iris translucency in Fuchs' heterochromic cyclitis.

PURPOSE: To measure intraocular stray light and to quantify translucency of the iris and the surrounding ocular wall in both eyes of patients with Fuchs' heterochromic cyclitis; to investigate whether differences in paired eyes could be measured in patients without heterochromia or with a minimal degree of iris atrophy. METHODS: Intraocular stray light was measured by means of the direct compensation technique. A modification of this technique was used to quantify translucency of the iris and the surrounding ocular wall. RESULTS: Intraocular stray light proved to be significantly higher in all patients with Fuchs' heterochromic cyclitis (both eyes) than in normal control subjects. Translucency of the iris and the ocular wall around it were increased in the patients with Fuchs' heterochromic cyclitis, including patients without heterochromia or with a minimal degree of iris atrophy. CONCLUSIONS: Quantitative analysis of translucency was used to determine iris depigmentation in vivo in patients with Fuchs' heterochromic cyclitis. This technique showed that the process of atrophy and depigmentation in patients with Fuchs' heterochromic cyclitis is probably not restricted to the iris, but also occurs in the surrounding ocular wall. More studies, including other uveitis groups, are necessary to investigate if this technique can be used as a diagnostic tool in Fuchs' heterochromic cyclitis.

An improved mathematical description of the foveal visual point spread function with parameters for age, pupil size and pigmentation.

An analytical description of the point spread function (PSF) for human foveal vision, together with its closed form two-dimensional Fourier transform, the modulation transfer function (MTF), is proposed. It also possesses an analytical line spread function (LSF) counterpart. It fits to both PSF and MTF experimental data and holds over the full angular and spatial frequency domain. Variation in the PSF and MTF descriptions with pupil size, age and iris/skin pigmentation are accounted for by analytical expressions in the parameters.

Stray light in radial keratotomy and the influence of pupil size and straylight angle.

Glare is a major sequela of the radial keratotomy procedure. We used the straylight meter to measure intraocular light scatter, which is the cause of glare, in eyes after radial keratotomy. This apparatus uses a direct compensation method to assess the amount of intraocular light scatter. Nineteen patients were tested. Nine individuals served as controls. The mean postsurgery time was 60 months. The influence of the number of radial incisions, the pupil size, and the angle of light entering the eye were evaluated with the straylight meter. The results showed straylight values for normal pupil size (mean, 4 mm) to be statistically significantly higher (P = .0044) only for the smallest angle of light deflection studied (3.5 degrees). For dilated pupils (mean, 8 mm), straylight values were statistically significantly higher (P = .00005) for all three angles of light deflection studied. The number of incisions showed no statistically significant relationship to straylight values. Average stray light values were increased by a factor of 1.4 for 4-mm sized pupils and 2.0 for 8-mm sized pupils. There was an overlap in straylight values between the patient population and the control population.

Intraocular light scattering in age-related cataracts.

Intraocular light scattering was studied in 34 controls and 65 patients with cortical, nuclear, or posterior subcapsular cataracts by measuring forward scatter and backscatter. Forward scatter was measured by the psychophysical direct compensation method. Backscatter was determined with the Lens Opacity Meter of Interzeag. Contrast sensitivity loss caused by forward scatter was assessed with a glare tester (Vistech MCT 8000). Mean forward scatter was in the upper range for subcapsular cataracts compared to nuclear and cortical cataracts. Experimental results of the glare test (the contrast loss) deviated systematically from expected results based on measured forward scatter. Mean backscatter was largest for nuclear, intermediate for posterior subcapsular, and almost zero for cortical cataracts. Thus, each cataract has a characteristic mean ratio between forward scatter and backscatter. However, this ratio varied considerably among individuals, especially for cortical and posterior subcapsular cataracts. As a rule, forward scatter cannot be derived from backscatter (or the slit-lamp image).

Clinical assessment of intraocular stray light.

A device that measures intraocular stray light for clinical use in, e.g., cataract evaluation by using the psychophysical direct compensation approach is described and evaluated.

Dependence of intraocular straylight on pigmentation and light transmission through the ocular wall.

The straylight function of the human eye depends on eye color, especially at larger angles of scattering. As a potential cause for this dependence, transmission of light through the ocular wall was measured, using a psychophysical method. For a light-blue eye effective transmission of the iris was 1% for red and 0.2% for green light. Also the eyewall around the iris transmits a significant amount of light. For the dark-brown eyes of pigmented individuals transmission is lower by two orders of magnitude. Although important, transmission proved to be only partly responsible for the pigmentation dependence, the other cause probably being reflection from the fundus.

Retinal contrast loss with non-monofocal IOLs.

Non-monofocal IOLs are designed to give simultaneously sharp images of distant and near objects. This is achieved by means of different focal distances for various portions of the light reaching the eye. As a result, for any given object, one part of the light will be properly focused, while another part is out of focus. This results in a sharp image superposed on a blurred image, causing contrast loss. The retinal contrast loss as a function of spatial frequency is derived in this paper.

Functional quantification of diaphany.

Intraocular straylight can be measured, in clinical as well as normal cases, by the direct compensation technique. Intraocular straylight is known to originate from the cornea, lens and fundus. We have studied a fourth source: the translucency of the iris and surrounding ocular wall. For lightly-pigmented normal eyes this source proved to be important. In the present paper results are reported from a patient with X-linked megalocornea. He had diaphany of the iris, as is common in these patients, and photophobic complaints. Quantitative measurements showed that the translucency was much increased so that the intraocular straylight was far above the normal level.

The intraocular straylight function in 129 healthy volunteers; dependence on angle, age and pigmentation.

The direct compensation method allows for an accurate (standard deviation below 0.05 log unit) determination of intraocular light scattering between 3.5 and 25 deg of scattering angle and is suitable for untrained subjects. The method was used to study population behaviour and individual variation in 129 volunteers between 20 and 82 yr of age, visual acuity equal to or better than one and no apparent eye pathology. The results indicate straylight to increase with the 4th power of age, doubling at 70. In addition to the age dependence, there was great variation between individuals. Part of this is due to negative correlation with pigmentation.