The effects of toxicological agents on the optics and mitochondria of the lens and the mitochondria of the corneal epithelium.

This review describes how the morphology and distribution of the mitochondria of the epithelium and the superficial fibre layers of the lens were studied using confocal scanning laser microscopy. This research was correlated with an effort to use the optical properties of the intact lens in culture as a proxy for the cornea in measuring ocular toxicity. In turn, this work led to the confocal study of the in vitro and then the in vivo cornea and their possible use in using confocal microscopy to evaluate the effect of various treatments on the integrity of the surface of the eye. Finally, confocal examination of the mitochondria of the lens has provided an avenue to the study of mitochondrial dynamics.

Dose-response of the cultured bovine lens to butyl, methyl and propyl parabens.

Pre-screening of cosmetic ingredients is vital for consumer safety. Previous in vivo techniques, such as the Draize test, have proved to be unreliable in predicting ocular irritancy and therefore there is a need for alternate testing methodologies. One such test is the scanning laser in vitro assay system which quantifies irritancy based on the focusing ability of the cultured bovine lens. In combination with confocal microscopy, a more thorough documentation of ocular irritancy can be achieved. This study investigates the response of cultured bovine lenses over time to butyl, methyl and propyl parabens, which are common antimicrobial agents found in cosmetic and ophthalmic products. The focusing ability of the lens was measured with an automated laser scanner over a period of 96 h. At 120 h post-treatment, the lenses were analysed by using a confocal laser scanning microscope to determine the characteristics of nuclei, and the morphology and distribution of mitochondria within the lenses. Irritancy to the three parabens was investigated at both an optical and cellular level. Each of the parabens was tested at 0.002% and 0.2%, where the 0.2% butyl paraben was found to be the most irritating.

Optical quality changes of the ocular lens during induced parr-to-smolt metamorphosis in Rainbow Trout (Oncorhynchus mykiss). Ocular lens optical quality during induced salmonid metamorphosis.

The effect of an induced salmonid parr-to-smolt metamorphosis ('smoltification') on the optical quality of the ocular lens was studied. In two separate experiments, rainbow trout (Oncorhynchus mykiss) parr were fed thyroxine in their diet to induce the metamorphosis. Lenses were excised at regular samplings during the treatment period and optically scanned using a custom scanning laser monitor. Radioimmunoassay was used to measure serum titers of thyroxine and 3,5,3'-triiodo-L: -thyronine. It was found that lens optical quality was consistently negatively correlated with 3,5,3'-triiodo-L: -thyronine levels, but not with thyroxine levels. To test if thyroid hormones are directly responsible for the change in optical quality, rainbow trout lenses were cultured for 72 h in a medium containing 3,5,3'-triiodo-L: -thyronine, but no effect was observed. The significance of these findings in the contexts of the fishes' visual capabilities and smolting physiology is discussed.

Long-term lens organ culture system with a method for monitoring lens optical quality.

The Scan Tox System is a method for monitoring lens optical quality (focus or lack of focus) in culture conditions, which mimic conditions inside the eye. The ocular lens is an ideal organ for long-term culture experiments because it has no direct blood supply and no connection to the nervous system. The Scan Tox System makes it possible to keep lenses for long-term studies of up to a few weeks. The use of cultured lenses, mainly bovine, replaces the need for testing the effects of potentially damaging agents on live animals. This optical monitoring apparatus uses a computer-operated scanning laser beam, a video-camera system and a video frame analyzer to record the focal length and transmittance of the cultured lens. The scanner is designed to measure the focal length at points across the diameter of the lens. The lens container permits the lens to be exposed to a vertical laser beam from below. The laser source projects its light onto a plain mirror, which is mounted at 45 degrees C on a carriage assembly. The mirror reflects the laser beam directly up through the test lens. The mirror carriage is connected to a positioning motor, which moves the laser beam across the lens. The camera sees the cross section of the beams and, by examining the image at each position of the mirror, Scan Tox software is able to measure the quality of the lens by calculating the back vertex distance for each beam position. The cultured lenses continue to maintain their original refractive function. When foreign substances are introduced to a cultured lens, the Scan Tox System measures the resulting optical response. This provides a very sensitive means to follow early damage to the eye lens. Because the lens is maintained in an intact state in solutions that are similar to those inside the eye, the lens retains its normal recuperative powers. So in addition to measuring early damage, this system allows measurement of recovery from damage.

Optical response of the cultured bovine lens; testing opaque or partially transparent semi-solid/solid common consumer hygiene products.

This study determines the relative ocular lens irritancy of 16 common partially transparent or non-transparent consumer hygiene products. The irritancy was found by measuring the changes in the sharpness of focus [referred to as the back vertex distance (BVD) variability] of the cultured bovine lens using a scanning laser In Vitro Assay System. This method consists of a laser beam that scans across the lens, and a computer, which then analyses the average focal length (mm), the BVD variability (mm), and the intensity of the beam transmitted. Lenses were exposed to the 16 hygiene products and the lens' focusing ability was monitored over 192 h. The products are semi-solids or solids (e.g. gels, lotions, shampoos). They are categorized into six groups: shampoos, body washes, lotions, toothpastes, deodorant, and anti-perspirant. Damage (measured by > 1 mm BVD variability) occurred slower for the shampoos, especially in the case of baby shampoo. The results indicate that shampoos exhibit the lowest level of ocular lens toxicity (irritability) while the deodorant is the most damaging.

Optical function and mitochondrial metabolic properties in damage and recovery of bovine lens after in vitro carbonyl cyanide m-chlorophenylhydrazone treatment.

In order to elucidate the correlation between lens optical function and metabolic function, in vitro bovine lens optical quality and mitochondrial integrity was measured following treatment with carbonyl cyanide m-chlorophenylhydrazone (the mitochondrial depolarizing agent, CCCP). The results indicate that in vitro exposure to CCCP resulted in concentration and time-dependent loss of sharp focus. The concentrations tested included 65.0, 32.5, 16.25 and 8.125 microm CCCP. Lenses treated with two lower concentrations show recovery from damage at the 24-h scan point. In lenses treated with 65 microM CCCP, mitochondria in lens epithelial and superficial cortical fibre cells appeared short and swollen. The results of this study indicate that lens optical function and mitochondrial integrity are closely correlated.

Suppression of post-vitrectomy lens changes in the rabbit by novel benzopyranyl esters and amides.

This study reports for the first time a therapeutic modality for the suppression of posterior subcapsular cataract (PSC) formation in an animal model (rabbit) of vitrectomy. This therapeutic modality may also have the potential to attenuate/prevent the high incidence of loss of vision due to cataract formation in patients that undergo vitrectomy. Unilateral, partial vitrectomy was performed on 2.5 month old Dutch Belted rabbits with vitreous replaced by either commercially available BSS((R)) or BSS PLUS((R)) (n=16). Alternatively, vitreous was replaced with a proprietary, modified BSS PLUS((R)) irrigating solution containing 1.25 microM AL-8417 (n=12), 5.0 microM AL-12615 (n=5) or 5.0 microM AL-17052 (n=9). Age matched, non-operated rabbits were used as controls (n=16). Lenses were analysed by correlative structural (light, scanning electron microscopic and three-dimensional computer-assisted drawings) and optical (low power helium-neon laser scan) quality analysis 6 months following surgery. Results demonstrate that vitreous replacement with an irrigating solution that contains the ester-linked benzopyran, AL-8417, the amide-linked benzopyran pro-drug, AL-17052, or its active metabolite, AL-12615, prevented abnormal post-vitrectomy lens growth, or fiber formation. Focal length variability (FLV) assessments (sharpness of focus) confirmed the beneficial drug effects detected morphologically, with FLV being essentially equal to that of age-matched, non-surgical controls. In contrast, lenses of animals with vitreous replaced solely with BSS((R)) or BSS PLUS((R)) exhibited significantly higher FLV than both age-matched controls and animals that underwent vitrectomy with drug-containing irrigating solutions. The ability of AL-8417, AL-17052 and its active metabolite, AL-12615, to suppress vitrectomy-induced posterior lens fiber changes appears to reside in their unique pharmacological profile, acting as antioxidant, anti-inflammatory and cytostatic agents.

Impairment of eye lens cell physiology and optics by broadband ultraviolet A-ultraviolet B radiation.

The phototoxicity of ultraviolet A (UVA) alone and UVA plus ultraviolet B (UVB) combined on cultured porcine lenses was investigated by analyzing cellular function as measured with a fluorescence bioassay approach and optical integrity, in terms of sharpness of the lens focus as measured with a scanning laser system. The bioassay consisted of carboxyfluorescein diacetate-acetoxymethyl ester and alamarBlue fluorescent dyes. Aseptically dissected porcine lenses were maintained in modified medium 199 without phenol red supplemented with 1% penicillin-streptomycin and 4% porcine serum. At 1 week of preincubation, baseline measurements were obtained. Then the lenses were treated with single exposures of different UVA and UVB energy levels. The lenses treated with 86 J/cm2 UVA alone showed a significant (P < 0.05) decrease in cellular and optical integrity at 48 h after exposure, whereas those treated with 43 J/cm2 UVA alone did not show significant phototoxic effect. Lenses treated with 15.63 J/cm2 UVA plus 0.019 J/cm2 UVB combined showed significant adverse effects beginning from 48 h after exposure. Also, there was no recovery. These findings show that a high UVA dose alone and relatively low UVA in combination with low UVB radiant exposure can impair lens cellular and optical functions, respectively.

Action spectrum and recovery for in vitro UV-induced cataract using whole lenses.

PURPOSE: To establish the in vitro action spectrum for acute UV cataractogenesis using whole cultured lenses. The recovery pattern of the induced cataract was also investigated. METHODS: Aseptically dissected porcine lenses were cultured in glass chambers. At 1 week, lenses were exposed to a predetermined UV energy (J/cm(2)) at specific wavebands ranging from 270 to 370 nm at 5- and 10-nm intervals. The UV energy was generated by a PRA integrated arc lamp system using a water-cooled 1000 W, high-pressure xenon lamp. The lamp output was limited using a deionized water filter, a monochromator, and secondary optics. An electronic shutter was used to control the exposure time. The median effective dose, ED(50) (i.e., UV energy threshold) for each waveband was statistically determined using probit analysis. Irradiated spots (3.06 mm(2)) on the lenses were monitored every 6 to 12 hours up to 48 hours postirradiation for any UV-induced opacity with a dissecting microscope and photomicrography. The ED(50)s were plotted against wavelengths to obtain the action spectrum. RESULTS: The threshold values for 270, 300, and 365 nm were 0.057, 0.069, and 137.19 J/cm(2), respectively. Permanent UV-induced cataract was obtained at twice the threshold values for UVB and UVA. CONCLUSIONS: An action spectrum for in vitro UV-induced cataract using whole cultured lens is established. These data are comparable to published in vitro (with isolated lens epithelial cells) and in vivo action spectra. The recovery pattern appears to be similar to the in vivo situation.

Refractive state and accommodation in the eyes of free-swimming versus restrained juvenile lemon sharks (Negaprion brevirostris).

Optical measurements of the refractive state of the eyes of various shark species typically have depicted sharks as hyperopic (far-sighted) with little evidence of accommodation (i.e. the ability to change focus for visualizing objects at different distances from the eye). In this study, we used infrared video retinoscopy to measure the refractive state in juvenile lemon sharks (Negaprion brevirostris). This technique allows dynamic measurement of refractive state in free-swimming animals as they pass by an aquarium window. We found that unrestrained lemon sharks are focused emmetropically relative to a 1-m distant photorefractor for the lateral visual field. However, when restrained either right side up or upside down (the latter inducing tonic immobility), the sharks become increasingly hyperopic, an artifact also reported in some other vertebrates. In addition, unrestrained lemon sharks display small amplitude accommodative excursions. Thus, refractive state measurements on restrained sharks in general may not reflect the natural, resting state of the shark eye, but rather, an induced hyperopia and lack of accommodative function. Such an artifact may be present in other vertebrate species, underscoring the need to obtain measurements of refractive state in unrestrained animals.

Effects of experimentally induced ametropia on the morphology and optical quality of the avian crystalline lens.

PURPOSE: To examine the effects of refractive error on avian lens morphology and optical quality. METHODS: Hatchling white leghorn chicks were unilaterally goggled for 7 days with either a form-deprivation goggle (n = 12), a -10 D defocus goggle (n = 12), or a +10 D defocus goggle (n = 12) to induce myopia and hyperopia. Optical quality of lenses (focal length and focal length variability) from treated and contralateral control eyes was assessed using a scanning laser apparatus. Lens morphology was examined by light and electron microscopy. RESULTS: Although the induction of refractive errors did not significantly alter lens size, shape, paraxial focal length, or average focal length, average focal length variability increased. Lenses from eyes goggled with form-deprivation and +10 D defocus goggles demonstrated a twofold increase in average focal length variability, when compared with their contralateral controls. The morphology of the lens is not altered by these experimental manipulations. CONCLUSIONS: This study provides evidence that the refractive development of the chick lens is not independent of the refractive development of the ocular globe and that chick lenticular development is influenced by both genetics and visual experience.

The relationship between rabbit lens optical quality and sutural anatomy after vitrectomy.

This study was conducted first, to characterize structural changes in rabbit lenses after vitrectomy; and second, to assess whether such changes correlate with a quantifiable compromise in optical function. Unilateral, partial vitrectomies were performed on 2.5 month old Dutch Belted rabbits (n = 64). Age matched non-operated rabbits (n = 32) were used as controls. Lenses were analysed by correlative structural (light, scanning electron microscopic and three-dimensional computer-assisted drawings) and optical (low power helium-neon laser scan) analysis at 1.5, 3, 6 and 12 months post-surgery (n = 16 lenses from operated animals and n = 8 lenses from non-operated controls at each time point). Results demonstrate that in rabbits lens growth, or fiber formation, is compromised after vitrectomy. From 1.5 to 12 months after surgery, lenses had progressively more crooked posterior line sutures with sub-branches of increasing size and number in successive growth shells. Quantification of lens optical quality specifically along and/or between these atypical suture branches and sub-branches revealed a significant increase in focal length variability (sharpness of focus) after vitrectomy. A peripheral zone of fibers with abnormal posterior ends was produced surrounding the pre-surgical lens mass. This additional zone of aberrant fibers was associated with a quantifiable degradation in lens optics. Studies on the prevention of post-vitrectomy lens changes in this rabbit model may yield useful information applicable to the human condition.

Age-related changes in human ciliary muscle.

PURPOSE: To examine the role of the ciliary muscle in accommodation and presbyopia. METHODS: Sixteen pairs of eyes from donors aged 1 to 107 years were treated with atropine or pilocarpine and then processed for light microscopy. Seven pairs were analyzed for treatment effects, including morphometric measurements of muscle dimensions, muscle fiber group area, and the percentage of connective tissue. RESULTS: The ciliary muscle shortened in length in response to drug treatment at all ages. The ciliary muscle of older subjects contained greater amounts of connective tissue and was shorter, wider and the internal apical edge moved forward. CONCLUSIONS: This study confirms previous reports that the human ciliary muscle retains its ability to contract throughout the lifespan. However, the ciliary muscle also displayed age-related changes, which may be partly accounted for by the forces exerted from the aging lens and zonules.

Optical properties of rainbow trout lenses after in vitro exposure to polycyclic aromatic hydrocarbons in the presence or absence of ultraviolet radiation.

The optical properties of rainbow trout lenses were investigated after in vitro exposure to polycyclic aromatic hydrocarbons (PAHs) and ultraviolet (UV) irradiation, both because PAHs frequently contaminate aquatic environments and because UV exposure has generally increased with the decline of the ozone layer. Lenses were exposed to UV irradiation for 12 hr while immersed in culture medium. UV irradiation, with or without the presence of PAHs, was accomplished with one UVA and one UVB photoreactor lamp to yield a photon fluence rate of 9.27 micromol m(-2)s(-1)UVA (UVA:UVB 10.8, radiant exposure of 13.4 Jcm(-1)). Individual PAHs studied were fluorene, fluoranthene and benzo(a)pyrene. In addition, lenses were exposed to a solution of creosote, a wood preservative used in the aquatic environment that contains many PAHs. All PAH exposures, including creosote, were carried out either in the dark or concurrently with UV irradiation. A scanning laser monitor system was used to evaluate the optical properties of lenses for up to 236 hr after the UV/PAH treatments. Mean focal length variability (FLV) increased with time after concurrent exposure to UV irradiation and high concentrations of either fluoranthene (4900 n m), benzo(a)pyrene (265 n m) or creosote (70 microg ml(-1)), with FLV values ranging from, 0.21-0.41, 0.21-0.64 and 0.15-0.22 mm, respectively, 72 hr after termination of the UV/PAH treatment. UV irradiation alone or exposure to PAHs in the dark brought about no changes in the optical properties of lenses. Also, fluorene in the presence or absence of UV had no effect, even at concentrations as high as 128 microm. Lenses were also unchanged by 12 hr exposures in the dark to solutions of either fluorene, fluoranthene, benzo(a)pyrene or creosote that had been previously UV irradiated for 12 hr. This meant that photomodified products of the individual PAHs or creosote were not cataractogenic and emphasized that simultaneous exposure to UV and PAHs or creosote was necessary for the increased FLV. The results point for the first time to an interaction between UV irradiation and PAHs as a potential contributing factor to cataract formation in fish.

Effect of maintaining rainbow trout in creosote microcosms on lens optical properties and liver 7-ethoxyresorufin-O-deethylase (EROD) activity.

Previously, exposure of fish to polycyclic aromatic hydrocarbons (PAHs) in both field and laboratory settings has been associated with eye damage, but this has only been expressed qualitatively. In this study, an automated scanning laser system has been employed to quantitatively evaluate changes in lens optical quality in rainbow trout (Oncorhynchus mykiss) following their in vivo exposure to creosote, which is a complex mixture with many PAHs. Rainbow trout were placed in 12,000-L outdoor microcosms dosed with 0, 3, or 10 microl/L liquid creosote for a 28-day period. Collected fish were examined for changes in focal length variability (FLV), lens size, and weight. These measurements were compared with induction of hepatic ethoxyresorufin-O-deethylase (EROD) activity and hepatic and water concentrations of priority pollutant PAHs. The optical quality of rainbow trout lenses was significantly reduced following creosote exposure, as indicated by increased FLV. Lens damage was significantly related to hepatic EROD activity, and both effects rose with creosote dose. Analytical measurements of microcosm water indicated elevated concentrations of PAHs in creosote-dosed ponds, including compounds capable of inducing rainbow trout EROD activity in vitro. Hepatic concentrations of PAHs were low and not related to creosote dose, likely due to rapid metabolism and elimination. This study demonstrates for the first time employment of a highly sensitive and quantitative technique to measure lens damage in fish exposed to contaminants in situ. The relationship between this effect and hepatic CYP1A activity may suggest a mechanistic linkage, which could lead to the use of EROD activity as an indicator of toxic effect rather than just chemical exposure.

Mitochondria of rat lenses: distribution near and at the sutures.

PURPOSE: This study is part of an effort to clarify mitochondrial distribution in the lens in order to better understand lens metabolic function. This study of the rat lens involves: 1) Using confocal microscopy, Rhodamine-123 and Calcium Green fluorescent dyes, to characterise the distribution of mitochondria and calcium in whole rat lenses of different ages in epithelial and superficial cortical fibre cells approaching sutures and 2) Using a scanning laser system to measure the optical quality at the sutures. METHODS: Lenses of rats from age 1 week to 22 months were pre-incubated for 24 hrs in 1.5 ml medium 199 (M199). Those exhibiting damage, as evaluated by protein leakage or visual opacities, were discarded. Lenses were labelled with 50 microg/ml Calcium Green for 45 min and/or 14 microM Rhodamine-123 for 25 min and embedded in 1% agarose in M199 for inverted laser scanning confocal microscopy with a 40 x water immersion lens. The lens optical properties were determined with a scanning laser system. RESULTS: Lens focal length variability significantly increased at the sutures of 13 month-old lenses, the only age investigated. An absence of both mitochondria and calcium was observed at the sutures in rat lenses of all ages. Elongated (up to 108 mm) mitochondria were present in superficial cortical fibre cells approaching the sutures of 16 month-old lenses. Calcium Green fluorescent staining was seen closer to the border of the suture, where mitochondria were absent. Along the axis, 1 week-old lenses showed a mitochondria free zone (MFZ) starting 177 microm below the lens surface, whereas in 22 month-old lenses the MFZ started only 29 microm below the surface. In the equatorial fibre cells, mitochondria were seen to a depth of 220 microm. CONCLUSIONS: Optical quality near and at the suture decreased in 13 month-old lenses despite the reduction in light scattering that should be associated with absence of mitochondria at the sutures. This suggests that mitochondrial loss in superficial cortical fibre cells may originate at the sutures and may compensate for loss of optical quality at the sutures.

Effect of diabetes and fructose/non-fructose diet on the optical quality (cataracts) of the rat lens.

PURPOSE: This study measures the effect of moderate and severe levels of diabetes on the optical performance of the rat lens, and evaluates the effect of dietary fructose on diabetic lens damage. METHODS: Moderate and severe diabetes were induced in 250 g rats (Harlan Sprague Dawley) with streptozotocin (35 and 55 mg/kg body weight iv). Animals were fed either a control (glucose/cornstarch) or a 40% (wt:wt) fructose and cornstarch diet and then sacrificed after 7 or 12.5 weeks. These two diets were also fed to two groups in which diabetes was not induced and these rats were also sacrificed at 7 or 12.5 weeks. Lenses removed from animals were analyzed in terms of average focal length (mm), focal length variability (spherical aberration, mm) and relative transmission of light (scatter or number of pixels excited by a refracted laser beam) using an automated laser scanning system. RESULTS: Diabetes disrupted rat lens optical function, both at 7 and 12.5 weeks, as indicated by an increase in focal length variability (FLV). This was true for control and fructose diets. For example, after 12.5 weeks on the diets average FLV values of 0.10 +/- 0.00 mm [n = 9], 0.11 +/- 0.01 mm [n = 9],(control and fructose diets, no diabetes) and 0. 48 +/- 0.04 mm [n = 10], 0.95 +/- 0.11 mm [n = 9], (control and fructose diets, severe diabetes), were measured. The difference between control and fructose diets was significant at 12.5 weeks in the severe diabetes group (p

Afocal magnification does not influence chick eye development.

In defocus-induced ametropia experiments, retinal blur circles are a likely source of information as to the magnitude but not the sign of the defocus. However, magnification (and minification) produced by the lenses may be a cue. In this study, 1-day-old broiler chicks (N = 13) were treated monocularly for 7 days with special goggles containing approximately afocal iseikonic lenses which were designed to produce 10% retinal image magnification. This is a little less than the magnification produced by +10 D defocusing lenses used to produce about 10 D of hyperopia in earlier work. Intraocular dimensions of both eyes were measured by A-scan ultrasonography on the first and last day. Refractive states of both eyes were measured daily with a retinoscope and trial lenses. After the birds were sacrificed, the eyes were enucleated, weighed, and measured with calipers. Before the treatment there was no difference in the refractive state or dimensions of the right and left eyes. After 1 week of goggle wear there was still no significant difference between the eyes in spite of the magnification produced by the goggles. These data suggest that factors other than magnification are responsible for the ability of the eye to respond to the sign of defocus.

The internalization of posterior subcapsular cataracts (PSCs) in Royal College of Surgeons (RCS) rats. II. The inter-relationship of optical quality and structure as a function of age.

PURPOSE: The Royal College of Surgeons (RCS) rat is an animal model for human retinal degenerative disease and posterior subcapsular cataracts (PSCs). The purpose of this study was to correlate the structure and optical quality of RCS lenses with PSCs as a function of their internalization, with normal, non-cataractous, age-matched control lenses. METHODS: Correlative light (LM), scanning electron microscopic (SEM), three-dimensional computer assisted drawings (3D-CADs) and low power helium-neon laser scan analysis were used to examine the structure and function of lenses. RESULTS: The optical properties (average focal length variability; sharpness of focus) of RCS rat lenses are quantitatively compromised by PSCs. Correlative LM and SEM analysis of RCS lenses at various stages of PSC internalization (1.5, 3, 6, 9, 12 and 15 months of age), revealed that the sutures formed by additional fiber growth were progressively more abnormal. During PSC internalization, two to nine small suture branches were formed and arranged in modified line to multiple y configurations rather than the normal three branch y sutures. These temporal changes were also chronicled in animated 3D-CAD videos derived from lens reconstructions based on LM and SEM micrographs from the selected time points stated above. However, laser scan analysis also revealed that as the PSCs of RCS rat lenses were progressively internalized, there was a steady improvement in total sharpness of focus that reached normal levels by 12 months of age. The correlation of laser scan and structural data from specific regions of lenses revealed the following: 1. The abnormal posterior sutures of RCS rats with internalized PSCs effect a greater reduction in optical quality than normal posterior sutures of age-matched controls; 2. However, the resulting abnormal suture plane area was cumulatively similar to that of age-matched controls; 3. Thus, total optical quality was similar between RCS lenses with internalized PSCs and age-matched controls by 12 months of age. CONCLUSIONS: The results of this study show that RCS lenses with internalized PSCs can appear grossly, and indeed optically perform, at levels comparable to aged lenses. These findings are consistent with clinical observations of spontaneous recovery from PSC. The results suggest that human PSCs that occur as a consequence of retinal degenerative disease could also be the result of abnormal posterior suture growth. If this is proven to be the case, such PSCs may have some capacity for repair or recovery thereby obviating their surgical removal.

Effect of age on the morphology and optical quality of the avian crystalline lens.

The effect of age on the avian lens was examined using White Leghorn chickens of five age groups: hatchling (n =19), 7 day (n = 15), 34 week (n =10), 2 year (n =24), and 5 year (n =25). The chick lens grows steadily up to 34 weeks of age, after which, the rate of growth slows down. During growth, average focal length of the lens becomes longer. However, no significant changes were noted between 2 and 5 year old lenses. An age related increase in average lenticular focal length variability (FLV) was observed, revealing that the optical quality of the lens decreases with age. Scanning electron microscopy demonstrated that: (1) the suture region of the lens becomes more diffuse and less precise with age; (2) the central regions of younger lenses are oblate spheroids, while older lenses become more apple-shaped; (3) individual lens fibres in the young lens are crescent-shaped, while older lens fibres are square-bracket-like in shape; (4) the edges of individual lens fibres become more jagged and irregular with age; and (5) the layering of lens fibres is more disorderly in older lenses, in contrast to the parallel and organized layering of fibres in young lenses.