Angle of anterior chamber

This presentation gives a brief idea about angle of anterior chamber along with its structures and diagnostic methods to grade and visualize the structures.

1. Moderator: Dr. Deepika M Presenter: K. Sahithi Reddy 2K14, KAMS&RC ANGLE OF ANTERIOR CHAMBER Date: 10-07-2017

2. INDEX : Anterior Chamber Angle of anterior chamber Development Aqueous outflow system Importance of Angle of anterior chamber Diagnostic modalities

3. ANTERIOR CHAMBER : Anterior chamber is an angular space. It is the space formed Anteriorly by the posterior surface of cornea Posteriorly by the lens within the pupillary aperture, anterior surface of iris and a part of cilary body

4. Anterior chamber Is 3mm deep and it contains 0.25ml of aqueous humour . Anterior chamber depth is shallower in the hypermetropic eye than the myopic eye. It is also shallower in children and older people. Chamber depth decreases by 0.01mm/year of life

5. Chamber depth is slightly diminished during accommodation, partly by increased lens curvature and partly by forward translocation of lens. Chamber deepens by 0.06mm for each diopter of myopia.

6. Structures in the anterior chamber: 1. Schwalbe’s line 2. Trabecular Meshwork 3. Scleral spur 4. Anterior most part of ciliary body 5. Root of Iris

7. D evelopment : By 7 th week, angle is occupied by mesenchymal cells from neural crest cells to develop trabecular meshwork. In posterior aspect, iris is formed from advancing bilayered optic cup Corneal endothelium meets derivative of iris at 15 th week to demarcate the angle. A ngle deepening continues even after birth.

8. Schwalbe’s Line: This marks the anterior border of angle and represents termination of descemet’s membrane. Seen as glistening white line in gonioscopy .

9. Prominance of Schwalbe’s line is known as posterior embryotoxon , seen in Axenfield Reiger’s Anomaly.

10. Pigments along Schwalbe’s line are known as Sampaolesi’s line, seen in pigmentary glaucoma & pseudoexfoliation Syndrome.

11. Schwalbe’s line marks transition from T rabecular to cornea endothelium. Termination of the D ecemet’s membrane. Insertion of trabecular meshwork into corneal stroma .

12. TRABECULAR MESHWORK: It is a sieve like structure made u p of connective tissue lined by trabeculocytes , which have contractile and phagocytic properties. Its main function is in drainage of aqueous humour .

13. The meshwork is roughly triangular in cross section; Apex is at the Schwalbe’s line Base is formed by the scleral spur and ciliary body.

14. It is morphologically and functionally divided into 3 types : 1. Uveal meshwork 2. Corneoscleral meshwork 3. Juxtacanalicular tissue/meshwork

15. 1. UVEAL MESHWORK: Innermost part of TM It comprises of trabecular bands, which have a central core that mainly consists of collagenous fibers distributed with a few elastic fibers, and is lined by trabecular endothelial cells resting on a thick basement membrane The trabecular bands run mostly in radial fashion Trabecular apertures size is 25-75 micrometer. The trabeculocytes usually contain pigment granules.

16. 2. THE CORNEOSCLERAL MESHWORK: Consists of a series of thin, flat, perforated connective tissue sheets arranged in a laminar pattern The central core consists of collagenous and elastic fibres Each trabecular beam is covered by a monolayer of trabecular endothelial cells, supported by basement membrane. The pore size is smaller than the uveal meshwork (5-50micro metre )

17. Ultrastructure of Meshwork: Both uveal and corneoscleral bands are composed of 4 concentric layers 1. An inner connective issue core is composed of collagen fibres , with 64nm periodicity. The central core contains collagen types I and III and elastin. 2. Elastic fibres are arranged in a spiraling pattern with periodicity of 100nm.

18. 3. Cortical zone also called as glassy membrane 4. An outer endothelial layer provides a continuous covering over the trabeculae .

19. TRABECULAR ENDOTHELIAL CELLS Larger, more irregular and have less prominent borders than corneal endothelium. Joined by gap junction and desmosomes, which provide stability. 2 types of microfilaments: 1. Actin filaments : cell periphery, around nucleus, cytoplasmic processes. Cell contraction, phagocytosis, pinocytosis and cell adhesions. Regulating the shape and cytoskeletal organization.

20. 2. Intermediate filaments: Numerous, composed of vimentin and desmin . Imparts the contractile and motility functions.

21. 3. JUXTACANALICULAR MESHWORK: Also known as cribriform meshwork The outermost part of TM Lies adjacent to the inner wall of Schlemm’s canal It consists of a lose network of fine fibrils, elastic like fibres and elongated fibroblasts life cells and ground substance full of glycosaminoglycans and glycoproteins The spaces between cells are upto 10micrometre.

22. SCHLEMM’S CANAL Schlemm’s canal is a circular lymphatic like vessel in the eye that collects aqueous humour from the anterior chamber and delivers it into the episcleral blood vessels via aqueous veins. Schlemm’s canal is often divided into different parts by bridges or septa. The septa cross the lumen of the canal mostly in an oblique direction. They are often fixed to the outer wall of the canal at places where the collector channels begin. The structure of the outer wall of schlemm’s canal differs very much from that of the inner wall.

23. INNER WALL OF SCHLEMM’S CANAL The endothelial lining of the canal consists of a complete monolayer of flat endothelial cells that do not rest on a complete basement membrane. The subendothelial cell layer is not complete and consists of elongated, star like cells oriented predominantly in a radial anteroposterior direction The lateral walls of the endothelial cells are joined by tight junctions

24. Micropinocytotic vesicles are present at the apical and basal surfaces of the cells Some “vacuoles’’ have openings on the inner and outer sides, thus forming transcellular microchannels .

25. OUTER WALL OF SCHLEMM’S CANAL The endothelial lining is single- layered, with a well developed basement membrane The cells do not possess transcellular microchannels . The adjacent stroma consists of collagenous and elastic like fibers intermingled with fibroblasts.

26. COLLECTOR CHANNELS Schlemm’s canal is connected to episcleral and conjunctival veins by a complex system of intrascleral channels. Two systems of intrascleral channels have been identified: (a) Indirect system (b) Direct system

27. (a) INDIRECT SYSTEM Indirect system consists of 15-20, finner channels, which form an intrascleral plexus before eventually draining into the episcleral venous system

28. (b) DIRECT SYSTEM: Direct system consists of large caliber vessels, which run a short intrascleral course and drain directly into the e piscleral venous system, they are about 6-8 in number and also called as aqueous veins. These aqueous vessels terminate into the episcleral and conjunctival veins in laminated junction- it is called LAMINATED VEIN OF GOLDMANN

29. EPISCLERAL AND CONJUNCTIVAL VEINS Most aqueous vessel are directed posteriorly, with most of these draining into episcleral veins, whereas a few cross the subconjunctival tissue and drain into conjunctival veins

30. The episcleral veins drain into the cavernous sinus via the anterior ciliary and superior ophthalmic veins, While the conjunctival veins drain into superior ophthalmic or facial veins via the palpebral and angular veins

31. SCLERAL SPUR: Wedge shaped circular ridge. Pale, translucent narrow strip of scleral tissue. Scleral spur is composed of a group of fibres known as “scleral roll” Scleral roll is composed of 75-85% collagen and 5% elastic tissue.

32. ATTACHED: Anteriorly : trabecular meshwork Posteriorly : sclera and longitudinal fibers of ciliary muscle

33. Contraction of longitudinal ciliary muscle opens up trabecular spaces. Scleral spur prevents ciliary muscle from causing Schlemm’s canal to collapse. Individual scleral spur cells are innervated by unmyelinated axons. Varicose axons characteristic of mechano -receptor nerve measure stress in the scleral spur due to ciliary muscle contraction or changes in IOP.

34. CILIARY BAND: It marks the posterior most part of the angle. Represents the anterior face of ciliary body between its attachment to the scleral spur and insertion of iris. Width depends on the level of iris insertion. Wide in myopes Narrow in hypermetropes .

35. Ciliary band appears as a grey/dark brown band. It consists of longitudinal fibres . The contraction of longitudinal muscle, opens the trabecular meshwork and schlemm’s canal.

36. INNERVATION: Derives from the supraciliary nerve plexus and the ciliary plexus in the region of scleral spur. Both sympathetic adrenergic and parasympathetic and sensory innervation – present

37. Nerve endings contain mechanoreceptors which are located in scleral spur : act as proprioceptive tendon organs for the ciliary muscle, contraction myofibroblast scleral spur cells baroreceptor function in response to change in IOP

38. IMPORTANCE OF ANGLE OF ANTERIOR CHAMBER: For classification of glaucoma To note the extent of neovascularization To assess angle recession History or evidence of inflammation For evidence of neoplastic activity Degenerative or developmental anomaly For planning of treatment – iris neovascularization and laser procedure.

39. DIAGNOSTIC MODALITIES: Van- herick test Flashlight/ pentorch test Ultrasound biomicroscopy Optical coherence tomography (OCT) Gonioscopy

40. 1) VAN-HERICK TEST: It is a slit lamp estimation of angle To perform this test, slit lamp is made very bright and thin. It is offset 60 temporally to the slit lamp oculars. The temporal sclera is illuminated and the slit lamp beam is brought slowly towards the cornea until the anterior chamber is first identified. The thickness of the cornea is compared to the depth of the peripheral anterior chamber At, present, this test is most widely adopted method for evaluating the ACA in community optometric practice.

41. Corneal thickness: Chamber depth

42. GRADING:

43. 2) PENTORCH EXAMINATION: Depth of anterior chamber can be evaluated by focusing a beam of light on the temporal limbus , parallel to the surface of iris. In normal or deep AC the beam will pass through directly, illuminating the opposite limbus . In shallow AC, the anterior placement of or bowing forward of the iris obstruct the light and shadow is observed on the medial half of iris.

44. 3) ULTRASOUND BIOMICROSCOPY: UBM is a close contact (non-invasive) immersion technique. UBM is performed with the patient supine, positioning that theoretically causes the iris diaphragm to fall back. This deepens the anterior chamber and opens the angle. With UBM, only 1 quadrant can be imaged at a time. There is a risk of infection or corneal abrasion due to the contact nature of the examination.

45. 4) OPTICAL COHERENCE O TOMOGRAPHY(OCT) OCT is a non contact, non invasive light based imaging modality. Provides image resolution higher than that of UBM of anterior segment in cross section with AS-OCT, 4 quadrants can be scanned at once(multiple cross-sectional image of the anterior chamber angle) The working principle of OCT is similar to ultrasound which uses echoes to locate structures within the body.

46. 5) GONIOSCOPY: Gonioscopy is an essential diagnostic tool and examination technique used to visualize the structures of the anterior chamber angle. All gonioscopy lenses eliminate the tear-air interface by placing a plastic or glass surface adjacent to the front of the eye. Methods of gonioscopy : 1) Direct 2) Indirect

47. DIRECT GONIOSCOPY : Procedure Direct gonioscopy is most easily performed with the patient supine and in the operating room for an examination under anesthesia with 4% xylocaine . It is performed using a direct goniolens and either a binocular microscope or a slit-pen light . The lens is positioned after saline or viscoelastic is placed on the eye, which can act as a coupling device. The lens provides direct visualization of the chamber angle in an erect position

48. DIRECT GONIOSCOPY: Direct goniolenses : Koeppe Barkan Swan-Jacob

49. KOEPPE LENS: Koeppe lens is the prototypical diagnostic goniolens Koeppe gonioscopy is an unsurpassed method for viewing the chamber angle in the operating room.

50. Koeppe -type lenses are also quite useful for performing funduscopy . When used with a direct ophthalmoscope and a high-plus-power lens, they can provide a good view of the fundus, even through a very small pupil . These lenses are especially helpful in individuals with nystagmus or irregular corneas. Inconvenience is the major disadvantage of the direct gonioscopy systems.

51. BARKAN’S LENS: The B arkan goniolens has served as the prototypical surgical goniolens for surgical goniotomy . Has no rod SWAN-JACOB LENS: The Swan-Jacob goniolens has been modified for goniosurgery and is now one of the most popular models for angle surgery.

52. ADVANTAGES- Direct Gonioscopy : Observer’s height can be changed to look deep or get a better look at the angle structure’s As it is done in supine position it can be used for sedated, comatosed patients and in children Useful in examining the fundus with small pupil Straight on the view Panoramic view of the angle structure’s Comparison of angle recession Causes less distortion of AC

53. DISADVANTAGES: Inconvinient Special equipment is needed.

54. INDIRECT GONIOSCOPY : Procedure Indirect Gonioscopy is performed under the slit lamp . The patient and the examiner must be positioned in a comfortable fashion. A drop of topical anesthetic is then applied to the conjunctiva of both eyes. If using the Goldmann lens,  contact gel  is placed in the concave part of the lens. If using a Posner or similar type lens, a drop of artificial tears can be placed on the concave surface. The patient is then asked to open both eyes and look upwards. The examiner can then pull down slightly on the lower lid and places the lens on the surface of the eye.

55. The patient is then asked to look straight ahead. Most examiners choose to start with the inferior angle as it is usually more open, and the pigmentation of the trabecular meshwork is slightly more prominent, allowing for easier identification of the angle structures. Continue identifying all angle structures in all 4 quadrants, and then repeat with the other eye.

56. INDIRECT GONIOSCOPY: Indirect goniolenses : Goldmann Zeiss Sussman Posner

57. GOLDMANN LENS: It is a three mirror contact lens For examination of the entire ocular fundus and the iridocorneal angle. The advantage of a longer mirror is that it often permits binocular observation of the lateral sections of the ocular fundus

58. OBSERVATION: Central lens(1) - Posterior pole 73 mirror(2) - Equator 67 mirror(3) - Ora serrata 59 mirror(4) - Iridocorneal angle

59. ZEISS GONIOLENS: 4 identical mirrors angled at 64 which allow examination without rotation of the lens ADVANTAGE: Coupling material not required as the posterior curvature of the lens is equal to the corneal curvature Easy to perform when mastered Indentation gonioscopy can be performed DISADVANTAGE: difficult to master Does not stabilize the globe

60. SUSSMAN LENS: It is similar to Zeiss Lens except that it has no handle POSNER LENS: It is a modified Zeiss Lens with a handle

61. ADVANTAGES- Indirect Gonioscopy : Preferred by most Quick, convenient No special equipment needed Slit lamp is used, which provides variable magnification and illumination Can create corneal wedge Allows differentiation of appositional and synechial angle closure

62. DISADVANTAGES: Mirror image can be confusing Inadvertent pressure on the cornea: exaggerates the degree of angle narrowing in the G oldmann lens opens the angle in four mirror lenses

63. GRADING SYSTEMS:

64. REFERENCES: Glaucoma, 6 th edition, Comprehensive Ophthalmology, A K Khurana . Gross and Microanatomy of Angle of the Anterior Chamber, Glaucoma, Volume 1, 3 rd edition, Modern Ophthalmology, L C Dutta and Nitin K Dutta. Parsons’ Diseases of the Eye, 22 nd edition. Shield’s textbook of Glaucoma, 8 th edition.