The globe: A brief overview
Mary E. Shaw, Agnes Lee in Ophthalmic Nursing, 2018
The globe (Figure 5.1) is approximately 2.5 cm in diameter by the age of 3 years. It has three layers: The outer protective layer comprises the sclera for approximately its posterior five-sixths and the cornea for its anterior one-sixth. The cornea is clear to allow light rays through and is highly sensitive. The sclera is composed of tough white fibrous tissue.The middle layer is the pigmented vascular uveal tract. The choroid forms approximately the posterior four-fifths and the ciliary body and iris the anterior one-fifth. The iris is a diaphragm allowing varying amounts of light to enter the eye through the pupil in its centre. The ciliary processes produce aqueous humour and the ciliary muscles control the shape of the crystalline lens for focussing. The choroidal blood vessels supply the underlying outer layers of the retina.The inner layer is formed by the retina and is the nerve-ending layer containing rods and cones, which receive the light stimulus that is sent via the optic nerve to the occipital cortex for interpretation.
Perivascular Innervation In Special Sensory Organs With Particular Reference To The Presence of Neuropeptides
Geoffrey Burnstock, Susan G. Griffith in Nonadrenergic Innervation of Blood Vessels, 2019
The innermost layer of the retina receives its vascular supply from the central retinal artery. The outer part of the retina is supplied by the choroid, a vascular network consisting of small blood vessels and capillaries. The choroid receives its arterial supply via branches from the anterior and posterior ciliary arteries. The vortex veins provide the principal venous drainage. The blood vessels of the eye are under the influence of sympathetic nerves from the superior cervical ganglion, parasympathetic nerves arising from the oculomotor and facial nerves, and sensory nerves from the trigeminal nerve. By the use of the Falck-Hillarp18 and the glyoxylic acid19 histofluorescence methods, a dense network of perivascular adrenergic nerve fibers has been observed in the choroid. In addition, adrenergic nerve fibers are seen around blood vessels in the iris and in the ciliary processes. Electrical stimulation of the cervical sympathetic nerve causes vasoconstriction in the choroid, iris, and ciliary body.20,21
Principles and Methods of Ocular Pharmacokinetic Evaluation
David W. Hobson in Dermal and Ocular Toxicology, 2020
Diffusion is the primary means of movement through any of these tissues or fluids, but removal from the vitreous humor may occur via transport systems3 that can actively remove certain chemicals. The latter process of transport out of the eye can also occur in the ciliary processes,4 thereby presenting another means of reducing the posteriorly directed movement of a compound within the eye. Mechanisms exist, therefore, for the removal of certain substances from the eye across the blood-retinal and blood-aqueous barriers. These transport systems can have a pronounced effect on the composition of the aqueous and vitreous humor through the removal of selected chemicals. It is evident, therefore, that the effective delivery of any agent to the posterior pole of the eye by a topical drop delivery system requires facing a variety of different challenges from the tear film to the posterior uveal tissues.
Endoscopy-assisted pars plana lensectomy for brunescent cataracts in eyes with microcornea with microphthalmos
Published in Seminars in Ophthalmology, 2022
Deepika C Parameswarappa, Vivek Pravin Dave, Mudit Tyagi, Rajeev R Pappuru
The surgery was performed under local anesthesia. The steps, in brief, included sterile draping of the eye, and subsequently, three vitrectomy ports were made at a distance of 2.5 mm from the limbus as reported in previous studies with respect to short pars plana length in cases of microcornea and microphthalmos5–7(Figure 1b). Also, pars plana structures were visualized through transillumination from outside the sclera to avoid injury to the ciliary body and zonules.8 A 20 G endoscopy probe E4 Laser and Endoscopy System (EndoOptiks, Inc., Little Silver, NJ, USA) with light and video dual function was then introduced through the supero-nasal quadrant. With the aid of a camera connected, the infusion cannula was visualized with the endoscope. Subsequently, the ciliary processes and the retina were examined
Treatment of Nanophthalmos Cataracts: Surgery and Complications
Published in Seminars in Ophthalmology, 2022
Mei-Ying He, Jing-Ru Feng, Lu Zhang
Transscleral cyclodiode laser treatment is quick and remarkably effective for those who are not responsive to lasers and drugs, and who have poor visual function. This method safely reduces aqueous humor generation and correctly directs aqueous humor flow by shrinking the ciliary processes.59 Simultaneously, research has revealed that cyclodiode can be used as the primary treatment for refractory glaucoma with good vision.60 Anterior vitrectomy combined with hyaloido-capsulo-iridectomy is also a good treatment.61 Faisal et al.62believe that the ocular axis of the nanophthalmos is short, and the place 3.5 mm away from the corneal limbus may not be the flat part, but the retina. Thus, vitrectomy via anterior chamber approach and establishment of posterior and anterior chamber connecting holes through iris incision is a safer method.62,63
Current methods and new approaches to assess aqueous humor dynamics
Published in Expert Review of Ophthalmology, 2021
Carol B. Toris, Meghal Gagrani, Deepta Ghate
The circulation of aqueous humor in the eye (Figure 1) begins with its production by the ciliary processes and secretion into the posterior chamber at a steady rate (Fp, aqueous production). From there it flows into the anterior chamber (Fa, aqueous flow) or vitreous cavity (Fpost posterior flow) (Figure 2). Posterior flow cannot be measured noninvasively and, out of necessity, is usually ignored or assumed to be unchanged by any study manipulation. It is not currently described in the Goldmann Equation. Aqueous flow varies among animal species with the general trend of faster rates in larger eyes. The techniques to measure aqueous flow in use today include the noninvasive method of anterior chamber fluorophotometry, and two invasive methods of dye dilution, and constant flow infusion.
Related Knowledge Centers
- Anatomy
- Eye
- Choroid
- Bruch'S Membrane
- Zonule of Zinn
- Iris
- Lens
- Aqueous Humour