Type II collagen distribution during cranial development in Xenopus laevis

Epithelially expressed type II collagen is thought to play a prominent role in the embryonic patterning and differentiation of the vertebrate skull, primarily on the basis of data derived from amniotes. We describe the spatiotemporal distribution of type II collagen in the embryonic head of the African clawed frog, Xenopus laevis, using whole-mount and serial-section immunohistochemical analysis. We studied embryos spanning Nieuwkoop and Faber (1967) stages 21-39, a period including cranial neural crest cell migration and ending immediately before the onset of neurocranial chondrogenesis. Xenopus displays a transient expression of type II collagen beginning at least as early as stage 21; staining is most intense and widespread at stages 33/34 and 35/36 and subsequently diminishes. Collagen-positive areas include the ventrolateral surface of the brain, sensory vesicles, notochord, oropharynx, and integument. This expression pattern is similar, but not identical, to that reported for the mouse and two bird species (Japanese quail, domestic fowl); thus epithelially expressed type II collagen appears to be a phylogenetically widespread feature of vertebrate cranial development. Consistent with the proposed role of type II collagen in mediating neurocranial differentiation, most collagen-positive areas lie adjacent to subsequent sites of chondrogenesis in the neurocranium but not the visceral skeleton. However, much of the collagen is expressed after the migration of cranial neural crest, including presumptive chondrogenic crest, seemingly too late to pattern the neurocranium by entrapment of these migrating cells.

Evaluation of eyes harbouring perfluorocarbon liquid with standardized ophthalmic echography

For the detection of perfluorocarbon liquid (PFCL) left in the globe after vitreoretinal surgery, the method of standardized ophthalmic echography proved to be very helpful and effective. Larger amounts as well as only a few remnant drops of PFCL are represented in standardized A-scans and in contact B-scans by typical acoustic signals caused mainly by the slow velocity of ultrasound in PFCL. A safe differentiation from other intraocular conditions can be made with standardized echography.

The presence of L-carnitine in ocular tissues of the rabbit

Carnitine plays an important role in the metabolism of fatty acids. Its presence is considerable in tissues that use fatty acids as an important source of energy, such as the heart and skeletal muscle. Free carnitine and acid soluble acylcarnitines are present in various tissues of the rabbit eye. The lowest concentration of carnitine was observed in the vitreous humor and the highest in the lens. The ratio, acid soluble acylcarnitine/free carnitine, was lower in the cornea, aqueous humor, vitreous humor and lens, than in iris, ciliary body and choroid-retina. The topical administration of carnitine increased both free carnitine and acetylcarnitine in cornea, and only free carnitine in aqueous humor and choroid retina. Only after intravenous administration, did the levels of free and acyl-carnitine increase in the iris and ciliary body. Neither of the two carnitine species was changed in vitreous humor. The determination of the activity of carnitine acetyltransferase in the eye showed that in the ciliary body the values of activity were three times higher than those in the iris and choroid-retina. The elevated ratio of acid soluble acylcarnitines with respect to free carnitine in iris, ciliary body, choroid-retina as well as the higher activity of carnitine acetyltransferase in the ciliary body, suggest that carnitine plays an important role in those tissues of the eye where cells of a muscular nature are present and may represent, after esterification, an important energy reserve.

Pathogenesis of the platinum (cp) mutation, a model for oculocutaneous albinism

The platinum mutation at the C (albino) locus in the mouse is a potential model for oculocutaneous albinism in humans other than type IA (tyrosinase-negative) albinism. Although tissues from mice homozygous for the mutation display substantial tyrosinase activity, cutaneous and ocular pigmentation is severely restricted in affected animals. Using specific antipeptide antisera, we demonstrate that ocular extracts from wild-type mice contain two isoforms of tyrosinase bearing either the amino-terminal PEP5 epitope or the carboxy-terminal PEP7 epitope. The latter isoform participates in a high-molecular-weight complex detectable on sucrose density gradients. In platinum mice, antiserum to the PEP7 epitope fails to recognize any protein species, and the high-molecular-weight form of tyrosinase is not detectable. Our results support a key role for this high-molecular-weight complex in melanogenesis, and suggest that mutations that interfere with the ability of tyrosinase to participate in a multimeric complex may be a cause of oculocutaneous albinism in people.

Distribution of collagen IV in human ocular tissues

PURPOSE

To examine the distribution of the collagen alpha 1(IV) chain and a novel collagen alpha(IV)-related chain in human ocular tissue.

METHODS

Two monoclonal antibodies, JK199 and M3F7, against the alpha 1(IV) chain, and one monoclonal antibody, JK132, against a novel alpha(IV)-related chain were used in the avidin biotin peroxidase complex procedure of immunohistochemical studies. In situ hybridization and reverse transcription polymerase chain reaction were used to examine the presence of alpha 1(IV) messenger RNA in corneal epithelium.

RESULTS

Our data indicate that monoclonal antibodies JK199 and M3F7 react with most ocular basement membranes, but not with those of corneal epithelium. Similarly, monoclonal antibody JK132 reacts with most basement membranes of ocular tissues, with the exception of the inner limiting membrane of neural retina, Bruch's membrane, and corneal epithelial basement membrane. To examine if the epitopes recognized by the monoclonal antibodies were masked in corneal epithelium, the tissue sections were subjected to limited enzyme digestion, that is, pepsin, hyaluronidase, trypsin, and pronase E, or chemical treatments such as 0.1 N NaOH or 6 M urea. Proteinase treatment removed the JK132 epitope from all ocular basement membranes examined. Despite the pretreatment, corneal epithelial basement membrane was not stained by any of the monoclonal antibodies. However, the alpha 1(IV) messenger RNA was detected in corneal epithelium by in situ hybridization and reverse transcription polymerase chain reaction. Western immunoblotting indicates the presence of the alpha 1(IV) and the novel alpha(IV)-related chain in the basal lamella of corneal epithelium.

CONCLUSIONS

The epitopes recognized by JK199, M3F7, and JK132 are masked in basement membrane of corneal epithelium. Based on the tissue distribution and partial amino acid sequences of peptides recognized by JK132, the novel alpha(IV)-related chain differs from other known alpha(IV) chains.

Characterization of glucose transporter isoforms in the adult and developing human eye

The expression of glucose transporter isoforms (Glut 1, Glut 3, Glut 4, and Glut 5) in the human eye was investigated at various ages ranging between 8 weeks gestation (first trimester) and adult using Western blot and immunohistochemical analyses. Glut 1 and Glut 3 expression and cellular localization patterns were similar to those of human brain. Glut 1 (50-kilodalton protein) was expressed by epithelial cells (retinal pigmented epithelium, choroidal, iridial, and pars planus), which form the blood-eye barrier, retinal Mueller cells, the lens fiber cells, iridial microvascular endothelial cells, and to a lesser extent by the outer segments of the photoreceptor cells in the adult eye. This pattern was conserved throughout development and was evident as early as 8 weeks gestation. In addition, the endothelial cells of vitreous hyaloid vessels expressed Glut 1 at 8 weeks gestation. Glut 3 (50 to 55-kilodalton protein) immunoreactivity was observed only in the adult inner synaptic layer of the retina. Neither Glut 4 nor Glut 5 was expressed in any occular tissue at any age examined. These results suggest that Glut 1 is the main glucose transporter of the human eye and that it is ontogenically conserved. In contrast, Glut 3 is associated with selective neuronal processes, and its expression is developmentally altered.

Expression of the rasT24 oncogene in the ciliary body pigment epithelium and retinal pigment epithelium results in hyperplasia, adenoma, and adenocarcinoma

We examined eye lesions in five lines of transgenic mice carrying the human rasT24 oncogene driven by the type I gamma glutamyl transferase (gamma GT) promoter. In three lines, hyperplasia developed as early as 11.5 days postconception in the outer neuroectodermal layer, which gives rise to ciliary body and retinal pigment epithelium. At birth, the eyes from many animals contained adenomas, and by day 27, mice developed invasive adenocarcinomas originating in the region of the ciliary body. Microphthalmia, cataracts, and chronic nongranulomatous inflammation involving the anterior and/or posterior segments of the eye were also found. gamma GT is detectable histochemically as early as 11.5 gestational days in the outer neuroectodermal layer and after birth is more abundant in the ciliary body than in the retinal pigment epithelium. Using a reverse transcriptase-polymerase chain reaction, we found that type I (but not types II or III) gamma GT RNA is made by the mouse eye; the gamma GT(I)rasT24 transgene transcription product was detected in the eyes of all five transgenic lines. The sequential progression of hyperplasia to invasive neoplasms in the ciliary body in response to gamma GT(I)rasT24 expression differs from the process in the kidney of these animals in which tubular hyperplasia and microadenomas with little evidence of progression are the major lesions.

Expression of activin mRNA during early development in Xenopus laevis

Activins are members of the transforming growth factor-beta superfamily, a class of peptide growth factors that can regulate the growth and differentiation of a variety of cell types. In mesoderm induction assays, activins A and B were shown to be very potent inducers and it was only recently demonstrated that they are crucial for initial mesoderm induction in Xenopus embryos. To determine the source of activin protein for initial mesoderm induction and to investigate whether activins may play further roles in embryonic development we have examined the localization of the mRNAs encoding the activin beta A and beta B subunits in Xenopus embryos. Activin beta A and beta B mRNAs are found in the follicle cells surrounding oocytes but not in oocytes themselves or fertilized eggs. During embryogenesis activin mRNA is first detected after the midblastula transition and expression increases as development proceeds. Activin beta B mRNA is homogeneously distributed during blastula and early gastrula stages but restricted to the dorso-anterior region in neurula stage embryos. At the early tailbud stage activin expression becomes confined to the brain, eye analgen, visceral pouches, otic vesicles, and the anterior notochord.

Distribution of epidermal growth factor in rat ocular and periocular tissues

Using a sensitive radioimmunoassay (RIA) specific for rat epidermal growth factor (rEGF), we investigated the presence of rEGF in a variety of rat ocular and periocular tissues. Immunoreactive rEGF (IR-rEGF) was present in tear fluids (25.5 +/- 5.8 ng/ml), exorbital lacrimal gland (6.73 ng/g wet weight), intraorbital lacrimal gland (2.80 ng/g wet weight), Harderian gland (1.90 ng/g wet weight), and conjunctiva (0.16 ng/g wet weight). EGF was not detectable in aqueous humor, cornea, iris and ciliary body, lens, or the posterior part of the globe (retina, choroid, and vitreous body). Gel exclusion chromatography and reverse-phase high-performance liquid chromatography revealed that IR-rEGF in the above ocular fluids and tissues was indistinguishable from standard rEGF. Using enzyme-linked immunohistochemistry, rEGF was demonstrated to be localized in the duct epithelial cells of lacrimal glands. These findings reveal that EGF is preferentially localized in the ocular surface and lacrimal apparatus.

The determination of 5-hydroxytryptamine, related indolealkylamines and 5-hydroxyindoleacetic acid in the bovine eye by gas chromatography-negative ion chemical ionization mass spectrometry

Methods were developed for the analysis of 5-hydroxytryptamine, related indolealkylamines (tryptamine, melatonin, 5-methoxytryptamine, N-acetyl-5-hydroxytryptamine and 6-hydroxymelatonin) and 5-hydroxyindole-3-acetic acid (5HIAA) in bovine retina, aqueous and vitreous humours. 5-Hydroxytryptamine and related indolealkylamines were extracted and derivatized to form their corresponding pentafluoropropionyl spirocyclic derivatives. 5HIAA was extracted and derivatized to the corresponding pentafluoropropionamide-trifluoroethyl derivative. Identification and quantitation by gas chromatography-negative ion chemical ionization mass spectrometry was made with reference to deuteriated internal standards. 5-Hydroxytryptamine was present in all (n = 34) retinal samples analysed (20.53 +/- 1.64 ng) while N-acetyl-5-hydroxytryptamine was detected in half of the samples of retina (0.06 +/- 0.02 ng). Melatonin (0.15 +/- 0.06 ng) and tryptamine (0.78 +/- 0.34 ng) were detected in only a small number of retinas. 5-Methoxytryptamine was not present in retina. 5-Hydroxytryptamine was also present in aqueous (0.76 +/- 0.17 ng ml-1 and vitreous (0.35 +/- 0.05 ng ml-1' humours from bovine eye. Tryptamine, melatonin, 5-methoxytryptamine and N-acetyl-5-hydroxytryptamine were not detected in bovine aqueous and vitreous humours. 5HIAA was found in both bovine aqueous (2.03 +/- 0.38 ng ml-1) and vitreous (0.65 +/- 0.06 ng ml-1) humours, but its consistent determination in retina was obviated by interference from spurious peaks.

[Value of leukotriene C4 in human subretinal fluid]

Concentration of leukotriene C4 (LT C4) in subretinal fluid and plasma of 12 patients with idiopathic retinal detachment has been studied. In 10 cases the subretinal fluid contained LT C4 (0.34 +/- 0.24 ng/ml) and concentration of this substance was about 10 times lower than that observed in plasma (4.05 +/- 0.83 ng/ml). The presence of LT C4 in subretinal fluid may result from retinal damage and it can be considered as an important prognostic factor.

Packaging of rhodopsin and porphyropsin in the compound eye of the crayfish

The distribution of 3-dehydroretinal (Ral2) in dorsal, middle, and ventral slices of eyes of the crayfish Procambarus clarkii was examined by HPLC. No pronounced differences were found. Similar results were obtained when the eyes were cut into anterior, intermediate, and posterior portions. Dichroic difference spectra were measured in single halves of microvillar layers of isolated rhabdoms and the proportions of rhodopsin (P1) and porphyropsin (P2) estimated by comparison with computer-generated mixtures of these pigments, whose spectra are known from previous work. The fraction of visual pigment that is porphyropsin appears to be uniform throughout individual retinular cells and among the retinular cells of individual rhabdoms, but various substantially among different rhabdoms from the same eye. The interommatidial variation in the amount of P2 greatly exceeds the gross regional variation in Ral2. This means there is an intermingling of ommatidia with different levels of P2. The variability in P2 among ommatidia is not likely to have important implications for the vision of the crayfish but suggests that in the metabolism of retinoids, individual ommatidia are quasi-independent metabolic units. The results are compatible with a single opsin for both crayfish rhodopsin and porphyropsin.

Isolation of Antho-RFamide related peptides from the eyestalks of blue crab

1. Two carboxyl-terminally amidated peptides (CP1 and CP2) were isolated from the blue crab (Callinectes sapidus) eyestalks by a method of carboxyl-terminal analysis. 2. The peptides were sequenced as pGlu-Gly-Arg-Phe-amide (CP1) and pGlu-Leu-Gly-Arg-Phe-amide (CP2). 3. Each carboxyl-terminus of the peptides was precisely determined by amino acid analysis utilizing phenylisothiocyanate derivatives. 4. CP1 was identical to the sea anemone neuropeptide, Antho-RFamide.

Synchrotron X-ray diffraction and histochemical studies of normal and myopic chick eyes

Synchrotron X-ray diffraction patterns were obtained from the cornea and posterior sclera of control and myopic chicks. No significant differences was found in the interfibrillar or in the intermolecular spacing of the collagen fibrils from the corneas of control and myopic chicks. The intermolecular spacing of myopic sclera was shown to be significantly (p < 0.01) higher than in controls. Sclera and cornea from normal and myopic chicks were stained for proteoglycans using the 'critical electrolyte' method of Scott and Orford (1981). In the sclera, two morphologically distinct types of proteoglycans could be distinguished; one small and usually elongated (approximately 20 nm), the other larger and irregularly shaped. The small proteoglycans were seen binding preferentially to the 'd' and 'e' bands of the collagen fibrils. Small proteoglycans were also present within the fibrils, these were usually approximately 10 nm in diameter although sizes up to 30 nm were observed. Longitudinal sections of fibrils revealed that these intrafibrillar proteoglycans were chiefly orientated parallel to the axis of the collagen fibrils, and preferentially located along the gap region of the fibrils. No difference was observed in the binding sites of the proteoglycans between normal and myopic sclera. The larger proteoglycans were also seen aggregated into clumps, which were usually associated with spaces between collagen bundles. The differences between control and myopic sclera appear to be quantitative rather than qualitative suggesting that the scleral expansion in myopia is an enhanced form of normal scleral growth.

Expression of hydra head activator in newt tissues and effects on limb regeneration

In this study, the presence of the hydra head activator (HHA) neuropeptide and its influence on regenerating newt limbs (Notophthalmus viridescens) was investigated. Immunohistological analysis has localized the HHA neuropeptide in the adult newt brain, eye, intestine, and regenerating blastema. Experiments in which 9 day limb regenerates were denervated and subsequently implanted with HHA-soaked beads suggest a slight progression of blastema growth compared to denervated controls.

Ocular and systemic determination of IL-1 beta and tumour necrosis factor in a patient with ocular inflammation

Cytokines such as interleukin-1 beta (IL-1 beta) and tumour necrosis factor (TNF) may play an important role in ocular inflammation. We studied a patient with clinical features of sympathetic ophthalmia secondary to previous penetrating ocular injuries, and compared the ocular and systemic levels of IL-1 beta and TNF to control serum, and correlated these findings to histopathological sections of the patient's eye. Histology showed the presence of a diffuse chronic inflammatory infiltrate within the choroid and in a perivascular distribution in the retina. The significantly elevated ocular and systemic levels of IL-1 beta and TNF suggest that there is not only a localized ocular response but a systemic response as well. The presence of IL-1 beta TNF may play a role in the pathogenesis of ocular inflammation once the blood ocular barrier has been breached and ocular antigens have been exposed to the systemic immune system.

Human eye: visualization of perfluorodecalin with F-19 MR imaging

Perfluorodecalin (PFD) was demonstrated in a human eye with fluorine-19 magnetic resonance (MR) imaging by employing a standard two-dimensional fast low-angle shot (FLASH) sequence. The presence and intraocular distribution of PFD were revealed despite the posterior eye segment being obscured by a narrow pupil, multiple small intraocular gas bubbles, and an intraocular hemorrhage. This examination can be performed with standard sequences on MR imaging systems equipped with a fluorine channel.

The eyespot of Chlamydomonas reinhardtii: a comparative microspectrophotometric study

The eyespot of Chlamydomonas reinhardtii is believed to utilize a rhodopsin-like pigment in its responses to light. This paper examines its eyespot by means of microspectrophotometry with the finding of an absorption spectrum with two bands, an A-band in the blue, and a B-band in the green. This spectrum is identical to that previously recorded from the eyespot of Euglena gracilis. As with Euglena the B-band was found to have dichroic character and its spectrum was similar to the absorption curve of rhodopsin. This A-B-spectrum was always recorded from a single granule in each cell. It is concluded that both E. gracilis and C. reinhardtii may utilize a rhodopsin-like pigment as the photopigment associated with the eyespot response to light. In both these algae a few particles in each cell were found whose spectra consisted of two other bands, C and D, blue- and red-shifted, respectively, relative to the eyespot A-B-bands. There is some reason to believe that the C-D-granules may also be involved in certain light-controlled activities of the cells.

A specific, sensitive, and rapid method for the determination of glutathione and its application in ocular tissues

A method for specific determination of glutathione (GSH) is described. This method utilizes the enzymatic conjugation of GSH to 1-chloro-2,4-dinitrobenzene through reaction catalyzed by glutathione S-transferase. The recovery of GSH as determined by this method is comparable to that in currently used methods. The method is specific for GSH determination. Other sulfhydryl (-SH) compounds including the protein -SH or beta-mercaptoethanol, which are often included in tissue homogenates, do not interfere with GSH determination. Acid extraction of the tissue is not required in this method and comparatively smaller amounts of tissue samples (as little as 20 microliters of a 10% w/v tissue homogenate) are needed for the analyses. The method when applied for GSH determination in ocular tissues yielded results in agreement with the reported values in literature. Evidence for the sensitivity, accuracy, and convenience of the method is provided by analysing the sample containing GSH in the range of 1-200 nmol by this method.

Detection of the mRNA encoding vitellogenesis inhibiting hormone in neurosecretory cells of the X-organ in Homarus americanus by in situ hybridization

Vitellogenesis inhibiting hormone (VIH)-mRNA in secretory cells of the eyestalk of Homarus americanus was detected by nonradioactive in situ hybridization (ISH) using two digoxigenin-tailed oligonucleotide probes deduced from the peptide sequence. Two distinct clusters of positive cells were observed in the medulla terminalis ganglionic X-organ (MGTX). Only one of them gave a strong immunoreaction after incubation with a specific polyclonal anti-VIH serum and corresponded to the conventionally described VIH producing cells. The significance of the cells reacting positively in ISH but not in immunocytochemistry (ICC) is discussed. Northern blot analysis using 32P-labeling confirms the specificity of the probes and indicates an approximate size of 2.5 kb for VIH mRNA.

The eyespot of Euglena gracilis: a microspectrophotometric study

The eyespots in cells of streptomycin-bleached strains and of dark-grown cultures of Euglena gracilis, were examined by means of fluorescence microscopy and microspectrophotometry. When viewed with light in the region of 380-500 nm, the stigma appeared as a dark spot. Adjacent to this was a second spot, not seen with white light, but which was seen to fluoresce when excited with radiation at 370 +/- 20 nm. This fluorescence proved to be polarized in contrast to other fluorescing bodies in the cell. The absorption curves, obtained by microspectrophotometry of individual eyespots, were found to consist of two spectral maxima, an A-band in the blue and a B-band in the green. Unlike the A-band, the B-band provided evidence of originating from an anisotropic structure. Relating these data to literature findings, we conclude that the B-band is the absorbance of a pigment in the quasi-crystalline paraflagellar body and the A-band perhaps a pigment in the orange-red stigma. The spectrum of the B-band does not appear to be that of a flavoprotein or of a free carotenoid but its resemblance to the spectrum of rhodopsin is significant in relation to published data for the Chlamydomonas eyespot that suggests the presence of a rhodopsin-like pigment as the photosensitive system responsible for phototaxis in this alga.

Regulation of methyl farnesoate in the hemolymph and mandibular organ of the lobster, Homarus americanus

Methyl farnesoate (MF) was measured in the hemolymph and mandibular organs (MO) of the lobster. Although a few animals had detectable MF levels in their hemolymph, this compound was undetectable (less than 0.4 ng/ml) in the hemolymph of most animals. One day after bilateral eyestalk ablation, MF was detected in the hemolymph of all animals, reaching variable levels (2.0-31.2 ng/ml) by the fourth day. Unilateral eyestalk ablation caused a smaller increase in hemolymph levels of MF. Similarly, the MF content of the MO, the only known site of MF synthesis, was low in intact lobsters (8.1 ng/gland) and was elevated in unilaterally and bilaterally eyestalk-ablated animals (54.1 and 106.9 ng/gland, respectively). When extracts of the sinus gland (SG), a source of neuropeptides in the eyestalk, were injected into bilaterally ablated lobsters, hemolymph levels of MF dropped to undetectable levels in 2 to 3 hr. The response to SG extract was dose dependent, and MF levels recovered by 12 to 24 hr after treatment. SG extract also lowered the MF content in the MO from 267.6 to 6.6 ng/gland after 4 hr. These results indicate that MF in the hemolymph and MO is negatively regulated by a factor(s) from the SG.

HLA DQA tissue typing of cadaveric eye bank donor material with polymerase chain reaction

It has been suggested that the provision of HLA matched tissue for corneal transplantation would be beneficial for graft survival especially in high risk patients. In this study we report the application of a polymerase chain reaction (PCR) based tissue typing procedure to type cadaveric donor material. Using beta-globin gene amplification as a test system we found that cornea, corneal rim, conjunctiva, sclera, rectus muscle, optic nerve and neural retina were all suitable for PCR amplification but DNA extracted from pigment epithelial cells and from the iris could not be amplified. HLA DQA typing results of 9 samples identified 5 alleles and 7 genotypes. In two cases the antigens detected by serology reflected the alleles detected by PCR. In a third case in which the class II serological typing was inconclusive we detected two DQA alleles by PCR. These alleles were consistent with those which would be predicted to be present on the basis of known linkage disequilibrium between HLA-Cw, B, DR and DQ. In this study we have shown that PCR based tissue typing is more sensitive and gives more detailed typing results than serology and would be suitable to type cadaveric donor material on a routine basis.

Localisation of prostaglandin F2 alpha and E2 binding sites in the human eye

Prostaglandin F2 alpha reduces intraocular pressure possibly by increasing uveoscleral outflow. To further understand the mechanism of its action binding sites for prostaglandin F2 alpha and, for comparison, prostaglandin E2 were localised in sections of human cadaveric eyes using an in vitro ligand-binding technique and autoradiography. Specific binding sites for both prostaglandin F2 alpha and E2 were co-localised at a high level in the areas of the ciliary muscles and iris sphincter muscles, and at a lower level in the iris epithelium and the retina. The results suggest that prostaglandin F2 alpha and also prostaglandin E2, could modulate uveoscleral outflow by binding to their receptors located on the ciliary muscles and inducing their relaxation.