Photoprotection and photoreception of intraocular lenses under xenon and white LED illumination

OBJECTIVE

To analyze the photoprotection and phototransmission that various intraocular lenses (IOLs) provide under the illumination of a xenon (Xe) lamp and white LEDs (light emitting diode).

METHODS

The spectral transmission curves of six representative IOLs were measured using a Perkin-Elmer Lambda 35 UV/VIS spectrometer. Various filtering simulations were performed using a Xe lamp and white LEDs. The spectral emissions of these lamps were measured with an ILT-950 spectroradiometer.

RESULTS

The IOLs analyzed primarily show transmission of nearly 100% in the visible spectrum. In the ultraviolet (UV) region, the filters incorporated in the various IOLs did not filter equally, and some of them let an appreciable amount of UV through. The Xe lamp presented a strong emission of ultraviolet A (UVA), and its emission under 300nm was not negligible. The white LED did not present an appreciable emission under 380nm.

CONCLUSIONS

The cut-off wavelength of most filters is between 380 and 400nm (Physiol Hydriol60C(®), IOLTECH E4T(®), Alcon SA60AT(®), Alcon IQ SN60WF(®)), so that their UV protection is very effective. Nonetheless, the IOL OPHTEC Oculaid(®) contains a filter that, when a Xe lamp is used, lets through up to 20% for 350nm and up to 15% for 300nm, which at this point is ultraviolet B (UVB). The OPHTEC(®) Artisan IOL has a transmission peak below 300nm, which must be taken into account under Xe illumination. White LEDs do not emit energy below 380nm, so no special protection is required in the UV region.

Ultraviolet radiation at Mediterranean latitudes and protection efficacy of intraocular lenses

PURPOSE

After determining the mean intensity of ultraviolet radiation to which the human eye is exposed at Mediterranean latitudes, this data is used to evaluate the efficacy of the ultraviolet filters incorporated into various intraocular lenses.

METHODS

Ultraviolet radiation measured at Mediterranean latitudes was used as a reference for the theoretical calculation of the amount of radiation to which the human eye is exposed. The spectral transmission curve from 290 to 380 nm was measured for 10 IOLs using a UV/VIS Perkins-Elmer Lambda 800 spectrometer.

RESULTS

At Mediterranean latitudes, at sea level, with a mean annual solar irradiation of 50 j/cm(2), the human eye receives a quantity of UVA and UVB that is lower than the threshold toxic dose for the rabbit crystalline lens (93 j/cm(2) for UVA and 6.45 j/cm(2) for UVB). However, at higher altitudes and with albedo approaching 0.9 (fresh snow), the amount of radiation increases, with duration of exposure potentially playing a significant role. The UV filters incorporated into the IOLs studied are, in general, protective against such levels of radiation.

CONCLUSION

At Mediterranean latitudes, at sea level, the amount of UV radiation to which our eyes are exposed is insufficient to damage the crystalline lens; however, at higher altitudes, the risk of such damage exists. UV filters incorporated into intraocular lenses are generally effective, since they filter all radiation with wavelengths under 380 nm.

Influence of the luminance level on visual performance with a disposable soft cosmetic tinted contact lens

The purpose of the present work was to study the effect on visual performance of wearing disposable soft tinted contact lenses for cosmetic purposes. Parameters such as contrast sensitivity (Vistech 6000), colour vision (Farnsworth-Munsell 100-Hue colour test), visual fields (static Goldmann perimetry) and subjective vision (what the wearer feels while wearing the lenses) were studied under different illumination levels in order to check for possible vision losses while wearing these contact lenses at low illumination levels. Sixteen emmetropic subjects were fitted consecutively with seven pairs of different colour lenses (Optima Colors lenses by Bausch & Lomb), and the experimental parameters were measured under four different illumination levels (60, 6, 1, and 0.1 cd/m2; but 15 and 0.3 cd/m2 for the static perimetry) The results obtained showed no statistically significant differences in visual performance between wearing the lenses and not wearing them (p > 0.01), except for the static perimetry, in which statistically significant differences (p < 0.01) occur at eccentricities greater than 30 degrees.

Perceptual feedback in multigrid motion estimation using an improved DCT quantization

In this paper, a multigrid motion compensation video coder based on the current human visual system (HVS) contrast discrimination models is proposed. A novel procedure for the encoding of the prediction errors has been used. This procedure restricts the maximum perceptual distortion in each transform coefficient. This subjective redundancy removal procedure includes the amplitude nonlinearities and some temporal features of human perception. A perceptually weighted control of the adaptive motion estimation algorithm has also been derived from this model. Perceptual feedback in motion estimation ensures a perceptual balance between the motion estimation effort and the redundancy removal process. The results show that this feedback induces a scale-dependent refinement strategy that gives rise to more robust and meaningful motion estimation, which may facilitate higher level sequence interpretation. Perceptually meaningful distortion measures and the reconstructed frames show the subjective improvements of the proposed scheme versus an H.263 scheme with unweighted motion estimation and MPEG-like quantization.

Optic nerve aspergillosis: report of a case diagnosed by fine-needle aspiration biopsy

The aim of this study was to describe the fine-needle aspiration biopsy (FNAB) procedure in patient with a optic nerve lesion. A case of optic nerve and brain aspergillosis, an infrequent condition that can mimic tumor or tumor-like lesions, is reported. The patient was studied by CT and MRI and definite diagnosis was established by means of an ultrasound-guided FNAB. Specimen preparation revealed the presence of multiple hyphae of Aspergillus fumigatus in the optic nerve lesion. The FNAB procedure is a safe and reliable diagnostic method for suspected intraorbitary tumors and tumor-like conditions especially when other less-invasive modalities have failed to establish the diagnosis and when cytologic confirmation is needed to implement aggressive therapy.

Spontaneous enterourachocutaneous fistula in Crohn's disease: sonographic diagnosis

Spontaneous abdominal wall fistulas are rare in Crohn's disease. We report a case of enterourachocutaneous fistula in a woman with Crohn's disease and present the sonographic, computed tomographic, and sinographic findings.

Characterization of the visual performance with soft daily wear disposable contact lenses

We investigate the visual performance associated with adaptation to a daily wear soft contact lens on the human eye. For this purpose, we used four parameters, one of which was an objective parameter, while the rest were subjective parameters. The objective parameter was a single quality parameter, a Merit function (Mf) derived from the modulation transfer function (MTF) of the overall [eye + contact lens] system The subjective parameters were the visual acuity (VA), the contrast sensitivity function (CSF) and the standard adaptation criterion of Terry et al. (1993). The normality criterion for the MTF was determined by evaluating the fluctuations of the Mf over a day in five emmetropic observers. Fluctuations with no statistically significant differences in the merit function (p > 0.05) and their standard deviation (8%) defined our standard criterion. The CSF and the VA were similarly measured (for emmetropic observers). The results obtained with emmetropic observers allowed us to establish a standard criterion for the evaluation parameters we propose. When this criterion is applied to daily soft wear disposable contact lenses, their performance proves to be good, since both the objective (MTF) and the subjective parameters (CSF, VA, adaptation criterion) always lie within the range defined by our criterion.

[Sclerosing hepatocarcinoma not associated with hypercalcemia]

The sclerosing hepatocellular carcinoma is an unusual subtype of hepatocellular carcinoma characterized by an intense fibrous stroma in which the tubular structures are embedded. Histological diagnosis is difficult, and misinterpretation as cholangiocarcinoma or metastatic adenocarcinomas may occur. It usually presents on non-cirrhotic livers. Metastases located outside of the liver are frequent as well as hypercalcemia and low levels of serum phosphate. We report a case of this rare histopathologic subtype of hepatocellular carcinoma in a 35-year-old woman, asymptomatic and with no previous history of chronic liver disease. It was detected by a routine gynaecological ultrasonography. An important increase of serum alpha-fetoprotein was noted. Extension studies showed bilateral lung metastases. Several palliative therapies were tried out, including epirrubicin, with partial response. Twenty months after the diagnosis the patient's situation is nearly terminal.

A Study of the Abney Effect in Some Colour Atlases: Designing Opponent Variables and Hue Functions

The Abney effect in colour-appearance systems (Munsell, NCS) means that the lines for identical apparent hue (at constant lightness) do not coincide with the straight lines for constant dominant wavelength. The curvature of constant-hue lines in chromaticity diagrams reflects the fact that cone signals are nonlinear functions of the rate of photon absorption. The most widely used nonlinear intensity-response function in vision is the Naka - Rushton function, which in an intermediate range can be approximated by a square-root function. Our purpose has been to study the Abney effect in the Munsell and NCS colour atlases in order to develop a mathematical-physiological description on this basis, designing the redness - greenness and yellowness - blueness perceptual variables and the perceptual hue function in each colour system. The description is applicable to both biological and machine-vision systems.

Implementations of a novel algorithm for colour constancy

In agreement with the principles of the relativistic model proposed by Creutzfeldt et al., with the photometric rule (lightness anchoring rule) and with the influence of simultaneous contrast in the appearance of a visual scene, we propose a first-stage mechanism yielding substantial colour constancy. We have defined a set of first-stage colour descriptors, and to test their utility, we have performed a simulation using a Machine Vision System (MVS). The statistical stability of the descriptors for Munsell samples under different illuminants is good.

[Contribution of hepatic scintigraphy with Tc99m blood cells to the imaging diagnosis of cavernous hemangioma. Results in 48 patients]

Cavernous hemangiomas are the most common benign tumours of the liver, being the liver the most frequent organ affected by this lesions. We report 48 patients who underwent 99mTc-red blood cell (RBC) scintigraphy, after ultrasound or tomographic appearance of cavernous hemangioma. Scintigraphy findings in 29 of 48 patients (60.4%) were typical of cavernous hemangioma, hemangioma-positives, after scintigraphy (all true-positives). On clinical, ultrasound and in one case after surgery (exploratory laparotomy) the follow up was positive for hemangioma. Specificity of 100%. In the remaining 19 patients (39.6%) where hemangioma-negative lesions, 17 of 19 where true negatives and the remaining 2 where angiomas false-negatives, both of them were small lesions. The sensitivity for hemangiomas was 89.4%. To conclude with we would like to enhance the high specificity and sensitivity of 99mTc-red blood cell scintigraphy on the diagnosis of cavernous hepatic hemangioma (CHH). We highlight the utility of this specific imaging technique in the final diagnosis of CHH not requiring other invasive diagnosis tests, such as laparoscopy that in our study proved to be unnecessary.

Standard criterion for fluctuations of modulation transfer function in the human eye: application to disposable contact lenses

It is well known that the modulation transfer function (MTF) characterizes the optical quality of the eye. Recently, some objective techniques have been introduced in order to measure this function in vivo. These techniques could be employed to display the temporal fluctuations of the eye + compensation system and to isolate the effect of the compensation element provided that the standard fluctuations for a normal observer were known. In this work we carry out a study of the MTF of the human eye over a long period of time to quantify the standard fluctuations of the retinal image quality and to establish a standard criterion of normality. We have defined a single quality parameter from each measured MTF to simplify the analysis of the results. We have evaluated this merit function on normal observers three times a day for one month. As expected, random deviations from the mean value of the merit function have been obtained, although fluctuations with no statistical differences of the merit function (P value from ANOVA test P > 0.01) and the standard deviation of these fluctuations (5%) can be chosen as a standard criterion. We have used this result to study the behaviour of a time-varying compensation element: a disposable contact lens. The study of the eye + contact lens system has been carried out with four types of disposable contact lenses for one month. In spite of their generally good behaviour, statistically significant differences from the standard pattern can be observed. This superimposed continuous fluctuation can be due to lens-dependent processes.

Human contrast sensitivity in coherent Maxwellian view: effect of coherent noise and comparison with speckle

Lasers have been used in vision for measuring the neural contrast sensitivity function (CSF) by forming interference fringes on the retina. We distinguish among three kinds of illumination with lasers: incoherent (without noise), Maxwellian or coherent (with coherent noise), and diffuse coherent (with speckle). The three have different characteristics and different CSF's. A coherent imaging system is designed to measure the CSF with fully coherent illumination. This is the CSF of the whole visual system, although it is measured with gratings imaged on the retina. It therefore differs from the neural CSF's measured by other authors with partially coherent illumination. However, the neural CSF's are also obtained in this study with and without noise. The effects of coherent noise and speckle on both the visual system and neural sensitivities are studied and compared. Coherent noise differs from speckle in the following ways: (1) It behaves as a high-pass filter, reducing sensitivity in the low-spatial-frequency range, whereas speckle is a low-pass filter; (2) quantitatively, coherent noise reduces neural sensitivity by a factor k(m) with a maximum value between 4 and 6, whereas speckle reduces neural sensitivity by a factor ks with a maximum value of approximately 25 (1.4 log units) for a 3-mm pupil and up to 35 (1.55 log units) for a 1-mm pupil; (3) the masking effect of the coherent noise is affected by changes in luminance but not by changes in pupil diameter; however, the pupil size is the main parameter affecting the masking effect of the speckle.

Contact lenses: do they really change the opticalperformance?

In this investigation the quality of two types of optical correction, hydrogel contact lenses and ophthalmic lenses, was compared by measuring the modulation transfer function (MTF) of the correcting lens plus visual optics system using an objective method. A merit function was defined in order to allow the direct comparison between the optical performance with the two corrections. A study on 10 subjects was undertaken, measuring the MTF of both corrections by using the double pass method. The results show that the optical quality of contact lenses was higher than that with ophthalmic lenses. The contrast sensitivity function (CSF) and visual acuity (VA) were determined as subjective parameters of visual performance.

Influence of the tear film on optical quality of the eye

The optical quality of the tear film of the eye was tested by measuring the retinal image before and after the break-up time (BUT). An objective method was used based on the evaluation of the retinal image of a point test projected onto the fovea. The loss of an entire tear film would result in a decrease in the optical quality because of corneal irregularities and the formation of an irregular tear lens after the BUT. Our results confirm the expected loss both of non-contact lens wearers and contact lens wearers. Also, the fact that the optical deterioration found after the BUT is greater for contact lens wearers confirms that soft contact lens wear produces a disruption of the tears.

Cavernous hemangioma of the liver. Diagnostic value of 99mTc-labeled red cell scintigraphy: results in 28 patients

Cavernous hemangioma is the most common benign tumor of the liver, the organ in which these lesions are most often present. We report on 28 patients who underwent 99mTc-labeled red cell scintigraphy after ultrasound or computerized tomography images suggesting the existence of one or more hepatic angiomas. In 16 patients (57.1%), an accumulation of red blood cells was considered to indicate the existence of hemangiomas. On the basis of subsequent clinical follow-up, ultrasound studies, and in one case laparotomy, all were eventually confirmed to be hemangiomas. The specificity as 100%. In the remaining 12 patients (42.9%), red cell uptake was not observed and the findings were considered negative; in this group, there were 10 true negatives and 2 false negatives in which scintigraphy failed to detect the existing angiomas due to their small size and deep location. The sensitivity was 88.8%. On the basis of the results, it is concluded that labeled red cell scintigraphy is a highly sensitive and specific method for the diagnosis of cavernous hemangioma of the liver. It should be considered the method of choice when this lesion is suspected, thus avoiding the use of more invasive diagnostic procedures such as laparoscopy which, in our study proved to be unnecessary.

Chromatic Intensities with Achromatic Surrounds

Brightness changes induced in red or green tests by an achromatic surround were studied by a nulling method with a centre — surround spatial configuration. The amplitude of the cancelling modulation was found to increase linearly with the contrast of the inducing field when its mean luminance was constant. The quotient between the amplitudes of the cancelling and the inducing modulations increased with increasing test luminance and decreased with increasing mean luminance of the surround. For a given contrast, the amplitude of the cancelling modulation increased with the amplitude of the inducing modulation, except when the mean luminance of the surround was close to the test luminance, where an abnormally high value was found. With the nulling method, the values of the cancelling modulation were practically the same for the green and the red tests. Nevertheless, with a heterochromatic brightness-matching method, the luminance changes needed to match the test brightness depended on test chromaticity. At equal surround luminance, the greatest changes were for the green test and the smallest for the blue test, the red test being at an intermediate level. The results are consistent with previous studies and were fit by the model recently developed by B Spehar, J DeBonet, and Q Zaidi. In this model the total brightness induced by a surround is equal to a weighted spatial summation of the induced effects from each point in the surround with local luminance gain controls in the test and surround fields.

Influence of contrast on the recognition of defocused letters: a geometrical model

We show how contrast (C) affects the recognition of defocused letters. To do this, the maximum distance (threshold distance) at which a subject, with an induced refraction of -5.5 D, can recognize a letter was determined. Our results show that when C = 1, the recognition threshold distance is such that the ratio eta/xi, between the pseudoimage of the letter (eta) and the blur circle (xi), corresponding to any point of the letter at this distance is about eta/xi = 2; the exact value depends on the difficulty of recognition, in agreement with previous experiments. This ratio represents the sharpness of the image in a geometrical treatment of image formation, providing a geometrical criterion for recognition. Reduction in contrast can be compensated by improving the geometrical sharpness; i.e. bringing the object closer to the subject's are point. Our results show that the increment of eta/xi as a function of the contrast is between C = 0.1 and 1.0. We suggest that a similar geometrical criterion for recognition could be used for any contrast (at least down to C = 0.1 and defocus > 1 D), provided that the proper value of eta/xi is used in each case. On this basis we propose a purely geometrical model, which agrees well with the data and predicts the relationships between tolerance to defocus, contrast and visual acuity; including the well-known relation between visual acuity and defocus when contrast is unity.

Contrast sensitivity of the visual system in speckle imagery

The contrast sensitivity function (CSF) of the whole visual system is determined with the use of coherent diffuse illumination. This function provides supplementary data about the effect of speckle on the ability of the visual system to perceive the spatial information contained in an image. The results show that speckle not only prevents perception of the finest details (highest frequencies) but also reduces the visibility of lower frequencies (especially where contrast is low). The difference between the CSF's determined with and without speckle is quantitatively very important. And the ratio between the two CSF's is a measure of the retinal ability to perceive contrast in the presence of speckle noise. The influence of the pupil size and luminance level on the CSF with speckle is studied and compared with the influence of the same parameters on the classical CSF.

Influence of the contrast sensitivity function on the reaction time

The reaction time (RT) vs spatial frequency (SF) curve is determined, using gratings from 1 to 40 c/deg, at seven different contrast levels between 0.95 and 0.02. The form of the RT/SF function: (a) replicated the inverse of the contrast sensitivity function (CSF) at near threshold contrast levels; (b) behaved differently at higher contrasts, exhibiting two branches at contrast close to 1. The interpretation is that there are two factors determining this function: (1) the transition from the operation of fast transient channels at low SF to the operation of slow sustained channels at high SF, the transition taking place within a narrow SF band close to 6 or 8 c/deg (depending on the subject) and (2) the contrast attenuation by the optical and neural transfer function, operating throughout the SF range. At high contrasts, the effect of the first factor can be clearly observed, because the effect of the second factor does not change with spatial frequency except in a region where the RT/SF function changes rapidly. At lower contrasts, however, the second factor becomes increasingly relevant while the first becomes less and less observable.

Effect of color on contrast sensitivity with two different accommodative stimuli

We studied the influence of color and accommodation on the contrast sensitivity function (CSF). At the same time, we measured the effect of axial chromatic aberration (ACA) on the CSF. The CSF's of two observers were determined using red, green, blue, and white light, at 5- and 0.5-m viewing distances. At 5 m the CSF's were measured with natural vision and also with lenses which compensated the ACA. Results show that the effect of ACA on the CSF is to reduce the sensitivity to blue with respect to the red. The difference in sensitivity between these two colors is between 50 and 150% and varies with the frequency and the subject. When the ACA is compensated the influence of the color on the CSF is very small, in our experiment, and this result is discussed in relation to the compensating effects of chromatic adaptation of the color mechanisms. In near vision, the CSF's were measured with natural vision and also with the lenses required to give the same accommodative stimulus for all colors. We discuss the effect of accommodation on the CSF. For both far and near the results are compared with the CSF with white light.

Serum trypsin levels in acute pancreatic and non-pancreatic abdominal conditions

Serum trypsin levels have been estimated by radioimmunoassay in 26 healthy controls (248 +/- 94.9 micrograms/l; mean +/- s.d.), 12 patients with chronic renal failure (1100 +/- 584 micrograms/l), 34 with acute pancreatitis (1399 +/- 618 micrograms/l) and 23 with acute non-pancreatic abdominal conditions. Mean serum trypsin in acute pancreatitis and in chronic renal failure was significantly higher than in control group (P less than 0.001). Serum trypsin levels were well above the upper limit of normality in all patients with acute pancreatitis and in all but one with chronic renal failure. Serum trypsin was markedly raised in one patient with a traumatic haemoperitoneum and in one of the 11 with peptic ulcer perforation, and moderately raised in 3 of the 6 with acute cholecystitis. Determination of serum trypsin seems to be a specific test for acute pancreatitis, provided renal failure has been excluded. However, the authors suggest it should be prospectively measured in a larger series of acute non-pancreatic abdominal conditions.