Anatomy and physiology of Accommodation.ppt

Accommodation in eyes

1. ACCOMMODATION DR SANDEEP PANWAR

2. Source Adler’s Physiology of the Eye – 11 th Edition Clinical Optics (BCSC Section 3)/Refractive Surgery (BCSC Section 33) - American Academy of Ophthalmology

3. SCOPE Definition of Accommodation Relevant Terms and Definitions Mechanism of Accommodation Theories of Accommodation Components of Accommodation Anomalies of Accommodation

4. Definition of Accommodation Mechanism of altering refractive power of the lens by altering its shape in order to focus objects at variable distances Change in the dioptric power of the crystalline lens to obtain and maintain an in-focus retinal image of an object of regard at the high-resolution fovea

5. Accommodative Triad or “Near Response” Accommodation Pupil constriction Convergence

6. Relevant Terms & Definitions Far Point or Punctum Remotum - farthest point clearly seen with no accommodation Near Point or Punctum Proximum - nearest point clearly seen with maximum accommodation Range of Accommodation - distance between far point and near point, where accommodation is effective

7. Amplitude of Accommodation - dioptric power difference between rest and fully accommodated eye A=P-R (A - amplitude of accommodation; P - dioptric value of near point; and R - dioptric value of far point)

8. Accommodative Convergence/Accommodation Ratio ( AC/A Ratio ) - How much eye converge for each unit of accomodation Definition - number of prism dioptres of convergence which accompanies each dioptre of accommodation Normal Range - 3:1 to 5:1

9. Lead of Accommodation - the amount by which the accommodative response of the eye is greater than the dioptric stimulus to accommodation Lag of Accommodation - the amount by which the accommodative response of the eye is less than the dioptric stimulus to accommodation

10. Mechanism of Accommodation Dioptric change in optical power -ciliary muscle contraction Moves apex of ciliary body towards axis of eye Releases resting zonular tension around the lens equator Elastic lens capsule moulds Lens -more spherical and accommodated form

11. Lens Changes during Accommodation Diameter decreases Thickness increases Anterior lens surface moves anteriorly Posterior lens surface moves posteriorly Anterior & posterior surface curvatures increases Thickness of the nucleus increases, but without change in thickness of cortex Depth of anterior and vitreous chamber decreses

12. Unaccommodated VS Accommodated

13. Theories of Accommodation Helmholtz Hypothesis or Capsular Theory Schachar’s Theory of Accommodation Gullstrand Mechanical model of Accommodation Catenary or Hydraulic Suspension Theory Müller’s Theory of Accommodation Tschernig’s Theory of Accommodation

14. HELMHOLTZ “Capsular Theory”: He considered that lens was elastic and in normal state it is stretched and flattened by tension of the suspensory ligaments. During accommodation, contraction of ciliary muscle shortens ciliary ring and moves towards the equator of the lens. Relax the suspensory ligaments, relieving strain. Lens assumes more spherical form, increasing thickness and decreasing diameter.

15. Components of Accommodation Reflex Accommodation Automatic adjustment response to blur which is made to maintain a clear and sharp retinal image Convergence Accommodation amount of accommodation stimulated or relaxed associated with convergence Link between accommodation and convergence is known as accommodative convergence Expressed clinically as AC/A Ratio

16. Proximal Accommodation induced by the awareness of the nearness of a target independent of the actual dioptric stimulus Tonic Accommodation due to tone of ciliary muscle and is active in the absence of a stimulus Resting state of accommodation is not at infinity but at an intermediate distance

17. Clinical Assessment of Accommodation Assessment of NPA (near point of accommodation) and amplitude of accommodation Assessment of accommodative response Assessment of dynamics of accommodation

18. Assessment of NPA and Amplitude of Accommodation RAF or Prince’s rule - a sliding target with letters, numbers or fine lines is moved away or towards the eye until the nearest point is found at which it still can be seen clearly. NPA - marked in cms on one side of bar Amplitude of Accommodation - marked in dioptres on other side of bar Age corresponding to Accommodation - marked in years on third side of bar

19. Measurement of amplitude of accommodation using minus lenses Patient asked to fixate the best corrected near vision target at 40 cm distance Minus lenses of progressively increasing power are added till patient reports the first sustained blur Add power of this minus lens to +2.5 D (for 40 cm testing distance) is equivalent to amplitude of accommodation in dioptres

20. Pushup Test Patient asked to fixate the best corrected near vision target at a distance where the target is seen clearly Near vision chart is moved closer till patient reports first sustained blur NPA - linear distance measured between the chart and the patient’s eye amplitude of accomodation - inverse of near point distance(in meter)

21. Assessment of Accommodative Response (Dynamic Retinoscopy) Monocular Estimation Method (MEM) Retinoscopy Patient asked to fixate near target at 40 cm Retinoscopy using streak retinoscope Note lens power to attain neutrality if positive lenses attains neutrality- lag of accommodation If negative lenses attains neutrality- lead of accomodation

22. Nott Retinoscopy Retinoscopic reflex neutralised by moving the retinoscope rather than adding lenses For ‘with’ movement - retinoscope moved away till neutralisation For ‘against’ movement - retinoscope moved towards till neutralisation

23. Assessment of Dynamic Accommodation How quickly the eye can switch focus between near and far objects (binocular accomodative facility) Accommodative flipper of +2.00 DS with -2.00 DS is rapidly flipped between the two lenses Difficulty with plus lenses - Accommodative excess Difficulty with minus lenses - Presbyopia

24. Anomalies of Accommodation

25. Anomalies of Accommodation Diminished or Deficient Accommodation Physiological - presbyopia Pharmacological - cycloplegia Pathological Insufficiency of accommodation Ill-sustained accommodation Inertia of accommodation Paralysis of accommodation Increased Accommodation Excessive accommodation Spasm of accommodation

26. Presbyopia Presbyopia or eyesight of old age is a condition of physiological insufficiency of accommodation due to reduced amplitude leading to a progressive fall in near vision Begins between 40 to 45 years of age

27. Causes Age related changes-lens: ↓ Elasticity of lens capsule Sclerosis of lens substance Age related decline in ciliary muscle power-contribute causation of presbyopia: Uncorrected hypermetropia pre senile weakness of ciliary muscle Chronic simple glaucoma Symptoms Difficulty in near vision Asthenopic symptoms Intermittent diplopia Symptoms aggravated by fatigue ,illness, fever or other debilitating conditions Treatment Optical correction Surgical

28. Accommodation and Aging Duane’s Standard Curve of Accommodation Amplitude in Dioptres in relation to Age

29. Optical Treatment of Presbyopia Prescription of appropriate convex glasses for near work A rough guide for providing presbyopic glasses in an emmetrope can be made from patient’s age 45 years: +1.00 D to +1.25 D 50 Years: +1.50 D to +1.75 D 55 Years: +2.00 D to +2.25 D 60 Years: +2.50 D to +3.00 D

30. Basic Principles of Presbyopic Correction Refractive error for distance - corrected first Correction needed in each eye tested separately Near point fixed according to profession of patient Weakest convex lens -one can see clearly at near point prescribed Overcorrection -result in asthenopic symptoms Presbyopic spectacles may be unifocal, bifocal , multifocal and progressive

31. Surgical Treatment of Presbyopia Corneal procedu res Monovision Conductive Keratoplasty Monovision LASIK Presbyopic bifocal LASIK Corneal inlay Intracor femtosecond laser

32. Lens based procedures : Refractive lens exchange Mono focal IOLs Laser based corneal procedures Sclera based procedures : Ant ciliary sclerotomy Scleral spacing procedure Scleral ablation with Erbium (Er):YAG laser

33. Diminished Accomodation Insufficiency Accommodative power less than physiological limits for patients age Intermittent/constant Transient/persistent Causes Premature sclerosis of lens Weakness of ciliary muscle CF Headache Fatigue Irritability of eye Near work blurred Intermittent diplopia Tx Tx of cause NV specs Accn exercises Ill sustained Accommodative range –normal but can not sustain for sufficient time period Causes Accommodation fatigue- Stage of convalescence from debilitating illness Stage of gen tiredness Pt relaxed in bed CF Tiredness on Near work NV blurred Tx Curtailing near work Accn exercises Improved visual hygeine

34. Diminished Accomodation Inertia Difficulty to change the focus of the eye between near and far objects Causes prolonged near working CF Takes time and effort to focus a near object Tx Correction of refractive error Accn exercises Paralysis Cycloplegia-complete absence of accn Causes Drug induced-Atropine,HA,etc 3 rd CN Palsy CF Blurred vision Photophobia/Glare NV difficulty If due to 3 rd CN palsy-signs of 3 rd N palsy Tx Self recovery –drug induced , diphtheric cases Dark glasses Convex lenses for NV if palsy is permanent

35. Causes Young hypermetropes Young myopes Astigmatic error Presbyopes Use of improper/ill fitting specs CF Blurred vision Asthenopic symptoms Far and near point both brought nearer to eye NV difficulty Macropsia Miosis Tx OPTICAL: Cycloplegic refractive correction GENERAL: Near work cessation-for a period Causes Drug induced spasm-strong miotics(ecothiphate,DFP) Spontaneous spasm Iridocyclitis-ciliary spasm Spasm of near reflex Lesions of brainstem CF Blurred vision Asthenopic symptoms Near point abnormally close Macropsia Tx Relaxation of ciliary muscle by cycl oplegics Correcting specs Excessive Spasm Increased Accomodation voluntary Involuntary

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