Accommodation. Core Fall 2016 Lisa Ostrin

Transcription

1 Accommodation Core Fall 2016 Lisa Ostrin

2 Accommodation

3 Accommodation Helmholtz Theory Adrian Glasser The ciliary muscle contracts Zonular tension is released The lens capsule molds the lens

4 Accommodation An increase in dioptric power of the eye that occurs with the attempt to focus on near objects Near Distance viewing viewing Accommodated Relaxed

5 Goal of Accommodation Dynamically change focal length of the eye to bring diverging rays into focus to maximize retinal image contrast Cues to accommodation blur depth chromaticity ocular aberrations microfluctuations Candy and Bharadwaj, 2007

6 Types of Accommodation Tonic accommodation Proximal accommodation Blur drive accommodation Convergence accommodation

7 Near Triad Accommodation - Pupil constriction - Convergence Three physiological responses are neurologically coupled in the mid-brain Stimulating accommodation also causes pupil constriction and convergence Stimulating convergence also causes accommodation and pupil constriction

8 Accommodative Apparatus Anterior uveal layer (Iris controls amount of light entering eye, not an accommodative structure) Ciliary muscle controls accommodation and aqueous outflow Longitudinal fibers Radial fibers Circular fibers Ciliary processes controls aqueous secretion Zonular fibers Anterior Posterior Crystalline lens Lens Capsule Lens Substance

9 Accommodative Apparatus

10 Zonule Fibers and Ciliary Processes Ciliary process Anterior zonule Posterior zonule Retzius, From Gullstrand Appendix to Helmholtz Treatise of Physiological Optics, 1866 Hogan, Alvarado and Weddell, Histology of the Human Eye, 1971

11 Ciliary Muscle Multi-unit smooth muscle Innervated by CN III, parasympathetic fibers 3 parts Longitudinal aka Brucke s muscle, outer layer, runs from anterior to posterior along length of ciliary body Circular aka Muller s muscle, innermost bundles, run circumferentially, major arterial circle is just anterior Radial few in number, between longitudinal and circular

12 Ciliary Muscle Circular Radial Longitudinal Hogan, Alvarado and Weddell, Histology of the Human Eye, 1971

13 The Crystalline Lens Center point of anterior and posterior surfaces are the anterior and posterior poles, the axis is the line joining the poles Anterior surface (10mm radius of curvature) is less convex than posterior surface (6mm radius of curvature) Outer edges are the equator

14 Layers of the Lens Lens capsule outermost elastic layer Epithelium only on the anterior surface Lens fibers Cortex Nucleus innermost

15 Lens Capsule Acellular basement membrane that completely envelopes lens Thinnest at poles and equator Thickest in midregions Formed by lens epithelium anteriorly and lens fibers posteriorly Consists of about 40 lamella made up of reticular fibers (netlike or entangled) embedded in sulfated glycoaminoglycan Composed of collagen type IV Forms a barrier to bacteria and inflammatory cells Will allow diffusion of smaller molecules

16 Lens Position Lens is suspended and under tension during distance viewing During accommodation the ciliary muscle contract, releases zonular tension, and allows lens to fatten Space between ciliary processes and lens equator decreases throughout life as the lens grows

17 Mechanism of Accommodation

18 Mechanism of Accommodation

19 Innervation to the Anterior Uvea Peripheral nerve supply Sensory innervation From the trigeminal ganglion Convey afferent responses to mechanical, thermal and chemical stimuli Autonomic system regulation of cardiac muscle, smooth muscle and glands Sympathetic innervation - from the superior cervical ganglion Parasympathetic innervation EW nucleus to ciliary ganglion to short ciliary nerves

20 Innervation to the Anterior Uvea Sensory innervation Long ciliary nerves from the nasociliary branch of the ophthalmic division of CN V from the trigeminal ganglion Convey afferent responses to mechanical, thermal and chemical stimulation

21 Parasympathetic Pathway Edinger-Westphal nucleus pre-ganglionic CN III acetylcholine ciliary ganglion post-ganglionic short ciliary nerves acetylcholine remember: SLUD ciliary body, sphincter muscle

22 Sympathetic Pathway para- Superior cervical ganglion post-ganglionic through carotid plexus joins nasociliary branch Long ciliary nerves Dilator muscle Q: what happens in the eye with the fight or flight response?

23 Autonomic Neurotransmitters Sympathetic Noradrenaline, dopamine, seratonin, purines, neuropeptide Y, epinephrine, norepinephrine Pharmacological agonists: phenylephrine Pharmacological antagonist: timolol maleate Parasympathetic Acetylcholine, vasoactive intestinal polypeptide Pharmacological Agonists: pilocarpine, carbachol, echothiophate Pharmacological Antagonists: atropine, scopolamine, cyclopentolate, tropicamide

24 Autonomic Innervation Iris Sphincter and CB Parasympathetic innervation to ciliary body and iris sphincter Muscarinic receptor types 1-5 Neurotransmitter acetylcholine Agonists: pilocarpine, carbachol, echothiophate Antagonists: atropine, scopolomine, pirenzepine M 3 (2)

25 Autonomic Innervation Iris Dilator Sympathetic innervation to iris dilator Adrenergic receptors α1, α2, β1, β2, β3 Neurotransmitter noradrenaline Agonists: phenylephrine Antagonists: prazosin (α), timolol (β), propranolol (β) adrenergic α1

26 Chen, Schmid, Brown. The autonomic control of accommodation and implications for human myopia Development: a review. OPO; 23(5):

27 Parasympathetic EW nucleus III Ciliary ganglion Short ciliary nerves Ciliary Body/Sphincter M 3 Sympathetic cervical sympathetic trunk Superior Cervical ganglion Long ciliary nerves Dilator/BV α 1 Sensory CN V, ophthalmic division, nasociliary branch, Long ciliary nerves Iris, cornea, cb

28 How to Measure Accommodation Subjective Push Up Method The distance corrected subject moves a near letter chart towards her eyes until she reports first sustained blur. The reciprocal of the distance from the letter chart to the eyes in meters is expressed as accommodative amplitude in diopters cm: 10 cm: -1/0.215 m = 4.65 D -1/0.10 m = 10D

29 Push-up Accommodative Amplitude Duane, 1912

30 How to Measure Accommodation Subjective Push Up Method Relies on subject s ability to perceive blur Blur perception varies with each individual subject Includes a measure of the depth of field of the eye (which is not accommodation) In eyes without accommodation (presbyopes, multifocal pseudopkhakic eyes), this only measures depth of field of the eye Measurements depend on individual subject s interpretation of blur Measurements can vary depending on instructions given to subjects (first blur vs sustained blur)

31 How to Measure Accommodation Objective Trial Lens Method Minus powered trial lenses placed in front of the eye to defocus a distant letter chart. The subject accommodates to overcome the imposed blur and the response is measured with a Hartinger coincidence refractometer (static response)

32 The Stimulus Response Function

33 How to Measure Accommodation Grand-Seiko Autorefractor (Static) Stimulus-response function Win-Hall, Ostrin, Kasthurirangan & Glasser, OVS, 2007

34 Power Refracter (Dynamic) Kasthurirangan & Glasser, Vis Research, 2005

35 Subjective vs. Objective Measures Win-Hall, Ostrin, Kasthurirangan & Glasser, OVS, 2007

36 Presbyopia Age related decrease in accommodation Generally attributed to hardening of the crystalline lens Other factors change in geometry of zonular insertion to capsule loss of elasticity of the posterior attachment of the ciliary muscle to Bruch s membrane Duane, 1912

37 Presbyopia Massive Increase in Stiffness of the Lens A. Glasser, M.C.W. Campbell / Vision Research 39 (1999)

38 Presbyopic Correction Non-surgical spectacles contact lenses Surgical LASIK monovision IOL monovision or multifocal

39 Presbyopic Correction Surgical, dynamic accommodative IOL lens refilling scleral expansion

40 Rhesus Monkeys as Model of Human Accommodation Similar anterior segment anatomy and accommodative mechanism (Glasser & Kaufman, 1999) Receptor characteristics resemble those of humans (van Alphen, 1976) Develop presbyopia at a similar rate when adjusted for life span (Bito, DeRousseau, Kaufman, & Bito, 1982)

41 Rhesus Monkeys as Model of Human Accommodation P. L. Kaufman, L. Z. Bito, and C. J. DeRousseau. Trans Ophthalmol Soc U K 102: , 1982.

42 Edinger-Westphal Stimulation in Rhesus Monkeys

43 Edinger-Westphal Stimulation in Rhesus Monkeys Permanent indwelling electrode in the Edinger-Westphal (EW) nucleus Neuronally driven accommodation Efferent pathway similar in humans

44 EW Stimulated Accommodation Monkey # 38, Hartinger Hartinger coincidence voltage refractometer response function OD Under Propofol Accommodation (D) max supramax Current ( amps)

45 Infrared Photorefraction

46 Ciliary Process and Lens Edge Movement Swan-Jacob gonioscopy Lens reference mark circumlental space ciliary processes lens edge

47 Ciliary Process and Lens Edge Movement Unaccommodated Accommodated Ostrin & Glasser, Experimental Eye Res., 2007

48 Lens Position with Accommodation During EW accommodation, anterior surface moves anteriorly, posterior surface moves posteriorly Pharmacological accommodation may be different than EW driven accommodation Vilupuru and Glasser, 2005 Findl O, 2001

49 Lens Position with Accommodation EW and pharmacological stimulation were performed to produce maximum accommodation Biometry measured continuously with A-scan CUB Computer anterior and posterior corneal surfaces anterior lens surface posterior lens surface retina Anterior chamber depth Lens thickness Vitreous chamber depth Anterior segment length

50 Lens Surface Movement Towards the cornea Anterior lens surface Lens Thickness Posterior lens surface At Rest Max EW Supramax EW Carbachol Initial Carbachol Final Distance from Cornea (mm)

51 In Vitro Scanning Experiments Enucleate eye and isolate anterior segment, leaving accommodative apparatus intact Mount preparation in fluid filled chamber Direct laser through lens across the diameter of the lens Can be used to test pharmacologically or mechanically induced accommodative lens changes

52 Lens Scanning ScanTox TM, curtousey V Choh

53 Lens Scanning lens Negative Spherical Aberration

54 Lens Scanning Negative Spherical Aberration

55 Back Vertex Distance

56 Lens Stretching

57 Conclusions During accommodation the ciliary muscle contracts, the apex of the ciliary body moves towards the lens equator, zonular tension is released to allow the elastic capsule to mold the lens into an accommodated form lens thickness increases, lens diameter decreases and lens surface curvatures become steeper. accommodative physical changes in the lens are linearly correlated with the accommodative refractive change Objective measurements are essential for true accommodative measurements