Anatomy of eye, oculocardiac reflex

OPTHALMOLOGY ANATOMY OF THE EYEBALL, IOP�OCULO CARDIAC REFLEX

1. OPTHALMOLOGY ANATOMY OF THE EYEBALL, IOP OCULO CARDIAC REFLEX Dr. Smita Joshi (Professor) Dr Soumya Nath Maiti

2. INTRODUCTION Eyeball is a cystic structure, Although referred as a globe it is a blate spheroid in shape. It has two pole anterior and posterior. Antero-posterior diameter of the eye is 24mm

3. Layers of the Eyeball It has three concentric layers. Outer fibrous layer – Cornea , Sclera , imbus . Middle vascular layer [ uveal tract] – Iris , C iliary body and Choroid . Inner neural layer – Retina Containing Rods and cones photoreceptors concerned with visual function.

4. SEGMENTS ANTERIOR SEGMENT: Cornea to the lens. It as two chambers. Anterior chamber- from endothelium of cornea to endothelium of iris. Diameter is 2.5 mm and contains aqueous humour Posterior chamber- Iris epithelium to anterior surface of the lens.

5. SEGMENTS POSTERIOR SEGMENT : P osterior to lens which includes vitreous, choroid, retina, and optic disc.

6. TEAR FILM It has three layers. Outer lipid layer, middle aqueous layer, inner mucin layer. It forms the coat over the cornea and conjunctiva and protects it.

7. CONJUNCTIVA Derived from surface ectoderm. Translucent mucous membrane which lines the anterior aspect of the eye ball and posterior surface of the eyelid. Can be divided into three parts: Palpebral conjunctiva Bulbar conjunctiva Conjunctival fornix.

8. CORNEA It is transparent, avascular , elliptical in shape , being 12mm X 11mm in size. Innervated by ophthalmic division of trigeminal nerve. It has five layers Corneal epithelium, derived from surface ectoderm Bowman’s membrane Stroma } Descemet’s membrane} Mesoderm Endothelium }

9. SCLERA Dense opaque tough fibrous envelope and covers the posterior 5/6 th of the eyeball. It has three layers Episclera Sclera proper Lamina fusca Blood supply – episcleral and choroidal vessels Nerve supply – Short ciliary and long ciliary nerves.

10. UVEA The pigmented layer of the eye, lying beneath the sclera and cornea, and comprising Iris, Ciliary body choroid.

11. IRIS A free circular diaphragm with central opening called Pupil. Colour – brown , Pattern – Collarette . It has two muscles viz Sphincter pupillae (Circular muscle) –causes pupillary constriction. Dilator pupillae ( Radial muscle) – causes pupillary dilatation.

12. CILIARY BODY: Middle portion of uvea Pars plicata – about 70 plication , has ciliary process responsible for production of aqueous Pars plana – posterior smooth part, safe and avascular zone for pars plana lensectomy and vitrectomy procedures.

13. CHOROID It is posterior part of uvea . This is a vascular sheet which separates sclera from retina.

14. CRYSTALLINE LENS It is transparent biconvex structure derived from surface ectoderm. Dioptric power : 16 – 20mm. 9mm in diameter, 4mm in thickness suspended by suspensory ligament called zonules . Structure of Lens: Anterior lens capsule Anterior lens epithelium Lens Nucleus – consists of elongated lens fibres 64% water, 35% Protein ( crystallin ), 1% Lipids ( Cholesterol, sphingomyelin , lipoproteins)

15. VITREOUS CAVITY Contain vitreous humour which is transparent gel like structure. Composed of collagen fibers and hyaluronic acid. Mainly serves the optical medium. In addition, it mechanically stabilizes the volume of the globe and is a pathway for nutrients to reach the lens and retina.

16. RETINA Membranous light sensitive layer of the eyeball. Layered structure with several layers of  neurons. The only neurons that are directly sensitive to light are the photoreceptor cells, T wo types: the rods and cones

17. NORMAL FUNDUS PHOTOGRAPH Optic disc. Pink coloured, well-defined circular Area. All the retinal layers terminate except the nerve fibres, which pass through the lamina cribrosa to run into the optic nerve Macula. Deeper red than the surrounding fundus Situated at the posterior pole temporal to the optic disc. Fovea centralis is the central depressed part of the macula 1.5 mm in diameter and is the most sensitive part of the retina.

18. Intraocular pressure (IOP) Range 10 - 20 mmHg Increases with age Direct correlation with axial length Main determinant is aqueous humour Increased IOP impairs blood flow to the retina leading to loss of vision . 18

19. Circulation of Aqueous H umour

20. Events that Decrease IOP IV anaesthetics Volatile anaesthetics Mannitol Timolol Betaxolol NDMR Hyperventilation Hypothermia 20 Events that Increase IOP Succinylcholine Direct laryngoscopy Hypoventilation Arterial hypoxaemia Increased venous pressure

21. Oculocardiac reflex Incidence ---- 30% to 90% The oculocardiac reflex is most commonly encountered in pediatric patients undergoing strabismus surgery, although it can be evoked in all age groups and during a variety of ocular procedures, This reflex consists of a trigeminal (V1) afferent and a vagal (X) efferent pathway.

22. Oculocardiac reflex -Causes Reflex triggered by Pressure on globe Traction on the extraocular muscle ( Esp medial rectus ) as in strabismus surgery. Ocular trauma Severe pain Orbital compression due to haematoma or edema Procedures under tropical anesthesia Orbital injections Hypercapnia or hypoxemia

23. Oculocardiac reflex Bradycardia Bigeminy Ectopic Atrioventicular block Cardiac arrest

24. Pathway Stretch receptors--- present in Extraocular Muscle Afferent through short & long ciliary nerves . The ciliary nerve s will merge with ophthalmic division of the Trigeminal nerve at the ciliary ganglion. Gasserian ganglion. Nucleus of T rigeminal & vagus Efferent vagal fibres ↑ Para symp tone & Bradycardia

25. Treatment- Inform surgeon, Stop stimulation. Verify adequate ventilation & oxygenation Atropine (20 µg/kg) or glycopyrolate (10-20 µg/kg) In recalcitrant episodes, infiltration of the rectus muscles with local anesthetic . The reflex eventually fatigues with repeated tractionon the extraocular muscles.

26. Oculo -respiratory reflex Causes shallow breathing, reduced respiratory rate and even full respiratory arrest. Pathways are similar to occulo -cardiac reflex. Due to connection between trigeminal nucleus and pneumotactic centre Atropine is ineffective. Adequate ventilation.

27. Thank you!