Agarwal / Narang Video Atlas of Anterior Segment Repair and Reconstruction

Managing Challenges in Cornea, Glaucoma, and Lens Surgery
1. Auflage 2019
ISBN: 978-1-63853-660-4
Verlag: Thieme
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 234 Seiten, ePub

Disorders of the anterior segment are a leading cause of ocular morbidity. As a result of structural abnormalities associated with trauma, degeneration, developmental disorders, or iatrogenic causes, reconstruction is required. Significant breakthroughs have been made in anterior segment reconstructive approaches, including the use of stem cells, selective tissue transplant, glued lenses, and advanced suturing techniques. by renowned ophthalmic surgery pioneers Amar Agarwal, Priya Narang, and international contributors is the most comprehensive resource available to date on anterior segment surgery, reflecting cutting-edge innovations.

Five sections and 27 chapters organized by ocular anatomy provide in-depth coverage on reconstructive techniques of the cornea, iris, aqueous drainage, and lens. The book and videos describe and highlight diverse state-of-the-art anterior segment surgery procedures, including limbal cell transplantation, keratoplasty, pupilloplasty, and intraocular lens implantation in deficient capsules. Clinical pearls throughout the concise text provide invaluable insights on surgical nuances and managing potential complications.

Key Features

• Current and future cornea approaches including corneal endothelial reconstruction, pre-Descemet's endothelial keratoplasty, and keratoprosthesis
• Innovative iris techniques such as single-pass 4-throw pupilloplasty, iridodialysis repair, intraocular lens surgery, and complications and management of cosmetic iris implants
• Disease-related eye surgery including minimally invasive glaucoma surgery and intraocular lens fixation with double-needle technique
• 38 high-quality videos by t

Autoren/Hrsg.

Agarwal, Amar

Narang, Priya

Fachgebiete

• Medizin | Veterinärmedizin Medizin | Public Health | Pharmazie | Zahnmedizin Klinische und Innere Medizin Augenheilkunde, Optometrie
• Medizin | Veterinärmedizin Medizin | Public Health | Pharmazie | Zahnmedizin Chirurgie Neurochirurgie
• Medizin | Veterinärmedizin Medizin | Public Health | Pharmazie | Zahnmedizin Chirurgie Plastische, Rekonstruktive & Kosmetische Chirurgie

Inhaltsverzeichnis

Section I Reconstructing the Cornea
1 Limbal Stem Cell Transplantation "Evolution and Techniques"
2 Penetrating Keratoplasty
3 Deep Anterior Lamellar Keratoplasty
4 Descemet's Stripping Automated Endothelial Keratoplasty
5 Corneal Endothelial Reconstruction: Current and Future Approaches
6 Pre-Descemet's Endothelial Keratoplasty
7 Keratoprosthesis
8 Patch Grafts
Section II Reconstructing the Iris
9 Single-Pass Four-Throw Pupilloplasty
10 Iridodialysis Repair
11 Iris Cerclage: 360 Degree Running Pupil Margin Suture
12 Aniridia Intraocular Lenses
13 Iris Prosthesis Implantation
14 Cosmetic Iris Implant Complication and Management
15 Pinhole Pupilloplasty
Section III Reconstructing Aqueous Drainage
16 Minimally Invasive Glaucoma Surgery and Valves
17 Single-Pass Four-Throw Pupilloplasty for Angle Closure Glaucoma
Section IV Reconstructing the Lens
18 Jacob Paper Clip Capsule Stabilizer
19 Double-Needle Iris/Intraocular Lens Fixation
20 Glued Intrascleral Fixation of Intraocular Lens
21 Flanged Intrascleral Intraocular Lens Fixation with Double-Needle Technique
22 Iris Claw Lens
23 Purkinje Images for Tracking Pseudophacodonesis
24 Reconstructing the Posterior Capsular Barrier
Section V Miscellaneous
25 Anterior Segment Repair and Reconstruction in Traumatic Cases
26 Phacocele and Pseudophacocele
27 Trocar Anterior Chamber Maintainer

Leseproben

1 Limbal Stem Cell Transplantation “Evolution and Techniques”

Summary

Stem cells are “pluripotent” cells which are capable of differentiating and proliferating into multiple lineages. Thus, they have an important role in reparative process. They are present in the cornea (limbus), conjunctiva, iris, ciliary body, trabecular meshwork, lens, retina, choroid, sclera, and the orbit. In some it has an established role as in limbal stem cell deficiency whereas in other further studies are still going on as in retinal diseases including age related macular degeneration, retinitis pigmentosa and Stargardt’s disease, optic nerve disease, and glaucoma. Stem cells aims to provide a solution for diseases which have no cure at present and it will provide vision to such patients.

Limbal stem cells, limbal stem cell deficiency, cultivated limbal epithelial transplantation, simple limbal epithelial transplantation

1.1 Introduction

Identification of limbal stem cells, their harvesting, expansion, and finally transplantation for the treatment of a wide variety of ocular surface pathologies has been a landmark innovation in the field of ophthalmology.

Limbal epithelial stem cells are basically a subpopulation of basal cells of the corneal epithelium with certain differences, as identified by nuclear labeling studies. Stem cells for the corneal epithelium have been seen to be preferentially located in a region called “limbus” and share common features with various types of other epithelial stem cells (palm, skin, hair, intestine) in terms of preferred location, pigment protection, and growth properties, all of which play an important role in maintaining their “stemness.”1 Stem cells located at all these sites exist as clusters in the basal region of their epithelium. Pigmentation and vascularity protect and nourish them and provide a specific microenvironment for their survival.1 As evidenced by 3H-thymidine labeling, these cells are normally slow cyclers, but can be stimulated to proliferate in response to injury and various tumor promotors.1 By a process of asymmetrical division, these cells give rise to a progeny of cells known as the transient amplifying cells (TAC). The TAC, unlike the stem cells, are capable of rapid division, but have limited potential to multiple. The TAC then finally divide to form a progeny of cells known as the terminally differentiated (TD) cells.1 These properties of stem cells have been utilized by the researchers and clinicians, enabling them to culture these cells ex vivo and transplanting them to the affected site so that a small population of cells covers a much larger area of deficiency.

The corneal epithelium is a specialized structure with an exceptionally high regenerative capacity of basal cells and a turnover of 6 to 8 days. As per the Thoft’s X, Y, Z hypothesis, the mass of corneal epithelium does not change under normal circumstances.2 It is regulated by three separate, independent phenomena; the X component which is contributed by the proliferation of basal epithelial cells; the Y component, contributed by the centripetal movement of peripheral cells; and the Z component, representing epithelial cell loss from the surface. For normal homeostasis, the amount of cell loss must be balanced by the amount of cell formation; X + Y = Z.2

Limbus is a transition area between two different kinds of epithelial lineages; the conjunctiva and the corneal epithelium. It houses the stem cells for corneal epithelium located in specialized crypt-like structures known as the “palisades of Vogt.”3 These stem cells migrate centripetally and give rise to TAC, which reside in the basal layer of peripheral as well as the corneal epithelium. These cells become more mature as they migrate vertically into the suprabasal compartment of corneal epithelium to become TD cells.4

Limbal stem cell transplantation (LSCT) is currently the standard of care for treatment of eyes with limbal stem cell deficiency (LSCD). In eyes with unilateral involvement, the donor tissue is harvested from the unaffected fellow eye (autologous), while in patients with bilateral damage, the donor tissue is obtained from either a living related donor or from a cadaver (allogenic). The obvious advantage of using an autologous tissue over an allogenic tissue is the absence of immunological rejection, thereby avoiding the need for long-term systemic immunosuppression.5, 6 Harvesting of limbal tissue also carries a potential risk of induction of donor site complications such as conjunctivalization, perforation, filamentary keratitis, and scarring.7, 8, 9, 10, 11, 12, 13, 14, 15, 16 Various surgical techniques of LSCT have been evolved and modified from time and then to reduce these side effects and maximize the efficacy of procedure.

1.2 Evolution of Limbal Stem Cell Transplantation

Eduard Konrad Zirm, in 1905, performed the first full-thickness corneal transplant in a patient with bilateral severe lime burns.17 The graft stayed clear for the initial postoperative period, but later on failed. The evolving patterns over a period of time have led to our current understanding that keratoplasty performed in eyes with ocular surface disease carries an extremely poor prognosis due to epithelial healing problems.

Maintenance of normal corneal epithelial homeostasis is an essential prerequisite for graft survival. Continuous renewal of epithelial cells is done by the stem cells, which as per our current understanding are located in the basal layer of limbal epithelium. The search for this location, however, began in late 1970s when conjunctiva was thought to be the source of renewal of corneal epithelium.

Shapiro et al, in their animal experiments, observed that following removal of the corneal epithelium, epithelial cells of conjunctival origin cover the exposed corneal surface followed by a morphologic transformation to normal-appearing corneal epithelium, about 4 to 5 weeks later.18 This hypothesis was further supported by the observations that the conjunctival epithelium increases its mitotic rate in response to corneal epithelial injury.19 Based on these findings, the concept of conjunctival transplantation20 was proposed. For patients with bilateral ocular surface disease, keratoepithelioplasty21 was considered as a modality of treatment. Both surgical techniques were based on the realization of the fact that either the peripheral cornea or conjunctiva is the source of corneal epithelial renewal.

This hypothesis was modified by the experiments of Lavker and Sun while they were working on epidermal stem cells.22 The hypothesis that the epithelial stem cells are located in the limbal basal layer was finally given in 1986 by the findings of expression of 64K corneal keratin, which is a marker of advanced stage of corneal epithelial differentiation.23 The 64K keratin was found to be expressed by all layers of corneal epithelium, while in the limbal epithelium, it was expressed only in the suprabasal layer suggesting that these cells are biochemically more primitive than the corneal basal cells. Conjunctival epithelium was found to be K3 negative suggesting that the conjunctiva and cornea are two distinct types of cell lineages.

Kenyon and Tseng,24 who proposed the idea of limbal autografting, performed the first clinical translation of limbal location of epithelial stem cells in 1990, which was found to be much more effective than the conjunctival transplantation.25 LSCT further went a revolutionary change when Pellegrini et al first reported the use of cultivated stem cells obtained from a 2 mm2 limbal biopsy specimen.26 This was a groundbreaking event as it reduced the size of limbal tissue to be harvested for transplantation. The technique was popularized as cultivated limbal epithelial transplantation (CLET). Sangwan et al further modified the technique from cultivating the stem cells in a laboratory to direct utilization of limbal biopsy for the expansion of stem cells.27 This technique became popularly known as simple limbal epithelial transplantation (SLET).

1.3 Indications of Limbal Stem Cell Transplantation

LSCT is an established technique for ocular surface reconstruction in eyes with LSCD. This can occur either due to primary or secondary causes. The primary form is related to insufficient stromal microenvironment to support stem cell function. The causes include aniridia, congenital erythrokeratodermia, keratitis associated with multiple endocrine deficiencies, neurotrophic keratopathy, and chronic limbitis. The secondary causes are the more common form of insults and include various external factors which either acutely or chronically destroy the limbal stem cells. These include chemical or thermal injuries, ultraviolet and ionizing radiation, autoimmune disorders such as Stevens–Johnson syndrome, advanced ocular cicatricial pemphigoid, multiple surgeries, cryotherapy, chronic contact lens wear, and extensive/chronic microbial infections.28, 29, 30, 31

1.4 Clinical Presentation and Diagnosis of Limbal Stem Cell Deficiency

Patients with LSCD present with complaints of reduced vision, photophobia, watering, blepharospasm, and recurrent episodes of pain due to epithelial breakdown. Slit lamp biomicroscopic findings at slit lamp examination may include a dull and irregular reflex of the corneal...