Development of the connective tissue of the extraocular muscles and clinical significance.

Mesectodern is an accurate term to describe the cellular origin of the connective tissue of the eye other than the eye muscles and vascular endothelium. The present study demonstrates that the tendons of origin and insertion, as well as the belly of the extraocular muscle, develops at the same time.

A reappraisal of the development of the eyelids.

The eyelids develop from ectoderm and from mesoderm. This evolution passes through distinct phases of maturation. Contemporaneously, the anterior segment of the eye takes form. The role of the amniotic fluid in the development of the eyelids is considered. The purpose of this report is to describe the development of the eyelids. The evolution of the eyelids from early embryonic life through different stages of development to term is examined.

A re-evaluation of corneal development.

The corneal epithelium is initially a continuation of the surface ectoderm, but later on in development appears to arise from the superficial cells of the corneal stroma. The corneal epithelium varies in thickness depending on the status of the lids, viz either fused or open. When the lids are fused, the epithelium is only 2 to 3 layers in depth. When the lids are separated, a basement membrane is distinguishable and the epithelium is 4 to 5 layers in depth. Bowman's membrane develops from processes of the superficial mesenchymal cells of the stroma that become thickened and are arranged in the long axis of the corneal surface. The corneal stroma develops from in situ mesenchymal tissue and does not migrate from the limbal mesenchymal tissue. The attenuation of the central cornea, early in development, is due to the impingement of the lens against the developing cornea. The central constriction of the cornea has led previous observers to believe that the stroma migrates from the peripheral limbal area towards the center of the cornea. Descemet's membrane arises from processes of the deep mesenchymal cells of the corneal stroma. These processes thicken and become arranged in the long axis of the posterior surface of the cornea. The membrane is initially cellular, and well-defined septae are noted between the cells. With maturity, Descemet's membrane becomes a homogeneous structure. The endothelium is derived from the mesenchymal cells of the posterior stroma. These cells are initially cuboidal but then become flattened. During the early development of the cornea, the tunica vasculosa lentis may play an important role. It is suggested that the anterior chamber is maintained early on by a transudate from the vessels of the tunica vasculosa lentis. The vessels of the tunica vasculosa lentis are compressed by the vanguard of the optic cup against the equator of the lens. With regression of this vascular system, there is a simultaneous development of aqueous humor. The hydrodynamic force of aqueous production assists corneal molding by a vis a tergo affect. Pari passu with this hydrodynamic force, the corneal stromal fibers increase in length and width. The structures involved in aqueous humor production, viz the ciliary epithelium, and the aqueous humor drainage, viz the filtration angle, trabecular meshwork and aqueous veins, develop contemporaneously as the tunica vasculosa lentis regresses. The limiting and fixed stabilizing site is at the limbus, the site of insertion of the rectus muscles. At these sites a dimpling occurs as the cornea is enlarging.

The origins and insertions of the extraocular muscles: development, histologic features, and clinical significance.

The tendinous origins and insertions of the extraocular muscles were studied embryologically by macroscopic and microscopic methods. It is concluded from this investigation that these tendons of origin and insertion arise from mesenchymal tissue similar to that of their respective muscles. These tendon-muscle groups have developed from superior and inferior mesenchymal complexes. The origins of the extraocular muscles are attached to the periorbita by an interlocking of the tendinous and muscular fibers, which allows for mobility of the extraocular muscles in all extreme directions of gaze and also results in a strong mechanical mooring for these muscles. Avulsion at the origins of the extraocular muscles following severe traction or trauma is rare. The additional origin of the superior and medial rectus muscles to the dura of the optic nerve explains the pain that may occur on movement of the eye in optic neuritis. Optic nerve compression and thyroid myopathy is explained by mucopolysaccharide and inflammatory cell infiltration of the muscular interdigitations that extend up to the site of origin of the rectus muscles. Findings of this investigation suggest that the association of ptosis and superior rectus muscle underaction may be due to a persistence of fibrous tissue that has endured from embryologic development between the superior rectus and levator palpebrae superioris muscles. Superior oblique tendon sheath syndrome is explained by embryologic strands remaining between the tendon of the superior oblique muscle and the trochlea. The insertions of the rectus muscles extend from the equator of the eye to the limbus early on in development. By processes of differential degeneration between the sclera and the rectus tendon, posterior recession of the tendon from the limbus, and contemporaneous growth of the anterior segment of the eye, these tendons reach their adult location only between the ages of 18 months and 2 years. In strabismus surgery, measurements for muscle adjustments should be assessed from the limbus rather than from the sites of insertion of these tendons. In the series of patients with esotropia, no mechanical abnormalities were noted in relationship to the insertions of the medial or lateral recti muscles. Furthermore, no correlation was found between the site of insertion of the medial rectus muscle and the degree of esotropia.

A re-appraisal of the development of the anterior chamber.

The development of the anterior chamber passes through distinct well orchestrated phases. It is a dynamic transition from an embryonic cleft to the adult anterior chamber. The cornea, lens, tunica vasculosa lentis, the iris, the ciliary epithelium, and the trabecular meshwork all play important roles in the development of the anterior chamber. Apart from these morphological changes that occur, the hydrodynamics of the transudate (from the tunica vasculosa lentis) and the aqueous humor from the ciliary epithelium appear to be essential components in the maintenance of the integrity of the anterior and posterior chambers.

Ptosis and underaction of the superior rectus muscle.

It is suggested that the association of ptosis and superior rectus muscle underaction is most likely due to the common embryological origins of these two muscles from the same superior mesodermal complex.

Orbital tumor dissector and retractor.

An orbital dissector and tumor retractor are described. The instruments significantly decrease the amount of trauma to the orbital structures and improve visualization because of the suction that is connected to both the dissector and the tumor retractor.

McCune-Albright syndrome (fibrous dysplasia) associated with an orbital tumor.

Craniofacial fibrous dysplasia has rarely been described in the polyostotic form of McCune-Albright disease. The unique ophthalmic features of interest in this patient with McCune-Albright's disease was the presence of an orbital tumor that suddenly increased in size compressing the optic nerve. Prompt excision of the tumor resulted in restoration to normal vision.

Value of computed tomography for the diagnosis of a ruptured eye.

The diagnosis of scleral perforation of the globe following ocular trauma is often obvious on physical examination, but occult perforations occur frequently. In addition to locating intraorbital foreign bodies and associated facial bone fractures, computed tomography of the orbit can suggest an occult scleral rupture. Posterior collapse of the sclera causes flattening of the posterior contour of the globe, the "flat tire" sign. Other associated findings that are suggestive of scleral rupture are intraocular foreign body or gas, thickening of the sclera posteriorly, and a blood-vitreous fluid-fluid level.

A histopathologic study of the Choyce VIII intraocular lens.

We performed a postmortem ocular examination on a 52-year-old man who had had Choyce VIII intraocular lenses implanted in both eyes. Visual acuity with both lenses was 6/6 (20/20). There were no clinical complications before the patient's death. Marked stretching of the chamber angle occurred at all points of fixation, with ultimate loop fixation into the substance of the ciliary body and, in some instances, erosion close to the greater arterial circle of the ciliary body. Where iris tucking had occurred, the iris tucked over the foot of the lens was extremely thin with the foot and the tucked iris in the pars ciliaris region.

A reappraisal of the origin of human extraocular muscles.

It has previously been suggested that extraocular muscles develop from mesoderm surrounding the head cavities and grow anteriorly into the orbit. A reappraisal of 54 specimens ranging in size from 8 mms to term indicates that human extraocular muscles develop from the mesoderm within the orbit and that these muscles do not develop from the apex of the orbit and grow anteriorly. Furthermore, the origin, belly, and insertion of the extraocular muscles develop contemporaneously, and each individual muscle develops at the same time. The morphogenesis of extraocular muscles includes the stages of mesenchymal cell, early myoblasts cells, myoblast cell, fusion of myoblast cell, myotube cell, and mature muscle cell.

Exenteration of the orbit using a frontal periosteal flap.

The technique of exenteration of the orbit described is used for orbital malignancies confined to the orbit without lid involvement and without overt evidence of metastases. The exenterated orbit is covered by a periosteal flap derived from the frontal bone. The procedure is simple, shortens the duration of the operation and allows for both pre- and postoperative radiotherapy. The procedure is particularly useful in children because of the minimal blood loss compared with exenteration using a temporalis muscle flap.

Development and congenital abnormalities of the nasolacrimal apparatus.

The development of the nasolacrimal apparatus was reassessed based on the examination of serial sections done in 27 (54 orbits) embryos and fetuses ranging in size from 13.6 mm to term. In addition two adult specimens were examined. The entire nasolacrimal apparatus viz. canaliculi, lacrimal sac, and nasolacrimal duct develop contemporaneously. Canalization thereafter occurs throughout its length at the same time. The epithelium which lines the nasolacrimal apparatus abuts against the conjunctival epithelium superiorly in relationship to the puncta and the nasal mucosa at the opening of the nasolacrimal duct. These gossamer-like membranes perforate at term or soon thereafter. With the development of the face, the maxillary process grows medially to abut against, and then to override, the paraxial mesoderm of the nasolacrimal process. The nasooptic fissure is thus formed between these two mesodermal complexes. The surface ectoderm within the fissure thickens in a cord-like fashion and this is the analaga of the nasolacrimal apparatus. There is divergence of opinion as to the subsequent development of tear drainage system. A cord of epithelial cells forms from the nasal cavity and grows cephalad to become continuous with the main cord of buried surface ectoderm (Figure 1). It has been contended by Duke-Elder that the main epithelial cord then sends extensions laterally to form the superior and the inferior canaliculi. The inferior canaliculus extends more laterally than the superior canaliculus. At 3 months' development, canalization of the nasolacrimal apparatus is purported to occur in a segmental manner. These cavities then coalesce in a haphazard manner, finally forming a continuous tube. It is also suggested that the main core of buried epithelium canalizes from cephal caudalwards and that the epithelium arising from the nasal cavity canalizes in a reverse direction. The lacrimal sac then expands: the canaliculi canalize and the final section of the nasolacrimal duct to become patent is the opening into the inferior meatus of the nose below the inferior meatus of the nose below the inferior turbinate.U

Progress in the use of iodine therapy for tumours of the eye.

Developments in a new system of brachytherapy for tumours of the eye are reported. This involves the use of 125I sources with special screens and filters to avoid irradiation of vital structures and to produce a homogeneous radiation field. Methods for the treatment of tumours of the lids, conjunctiva, retina, choroid and lachrymal gland have been developed. Sixteen out of 20 treatments appear to have been successful. This system would seem to be a material advance on those previously reported.

Polyvinyl alcohol as a protective coating on intraocular lenses.

Sixty-eight intraocular lenses were implanted in cats to compare the efficacy of a new polyvinyl alcohol coating in protecting the corneal endothelium from lens-cell contact damage. The mean endothelial density after implantation of the coated lens was significantly higher than the cell density in those eyes receiving the uncoated lens. We saw no clinical signs of unusual inflammation; whole-eye histopathologic study disclosed no signs of inflammation or toxicity related to the coating. Ten coated lenses were placed in balanced salt solution or perfused with balanced salt solution at 0.5 mL/min. The coating remained intact for 60 minutes, affording corneal endothelial protection for this period. In a rabbit anterior chamber toxicity study, using balanced salt solution as a control, no differencs in reaction in the anterior chamber or intraocular pressure were noted.

Retinoblastoma: correlation of invasion of the optic nerve and choroid with prognosis and metastases.

The histological sections of 74 retinoblastoma patients were reviewed. The extent of optic nerve invasion was correlated with choroidal/scleral extension. Choroidal invasion carries 100% survival provided that the sclera, iris, and whole optic nerve are not also involved. Invasion of the optic nerve beyond the lamina cribrosa also carries 100% survival provided that the resection line is free and that invasion does not involve the sclera or iris. Plentiful rosettes were usually found in those tumours that had not extended beyond the choroid or as far as the resection line of the optic nerve and were therefore associated with a good prognosis. The absence of rosettes did not necessarily indicate a poor prognosis. The site of metastases was related to optic nerve and scleral/extrascleral extension. The various systems of staging retinoblastoma are compared, and a new system is proposed to cover the whole spectrum of the disease and to offer a reliable guide to prognosis and treatment.