Accomodation and its anomalies

Accomodation and its anomalies

1. Accommodation and its Anomalies Sahibzada  Hakim Anjum Nadeem Co- Incharge OTTC, Optician, Refractionist , COAVS CEO Anjum Eye Care & Optical Company Optometrist, Al- Khair Eye Hospital Lahore Email: [email protected]

2. D ioptric adjustment of the crystalline lens of the eye - to obtain clear vision for a given target of regard P rocess by which the refractive power of eye is altered - to ensure a clear retinal image Accommodation

3. In an emmetropic eye - parallel rays of light coming from infinity are brought to focus on retina being accommodation at rest - eyes can also focus diverging rays coming from near object on retina to see clearly due to ACCOMMODATION

4. Mechanism of Accommodation As a result Allowing near object to be focused clearly on retina Ciliary muscle contracts Ciliary ring shortens Increase in dioptric power Lens becomes spherical i.e. convexity increases Tension in capsule is relieved Zonules are relaxed Equator of lens move forward

5. With Age lens fibers & lens capsule lose elasticity the size & shape of the lens increase reduction of accommodative amplitude onset of presbyopia

6. Ocular changes during Accommodation Anterior r =11 mm Posterior r = 6 mm T = 4 mm

7. Ocular changes in Accommodation Slackening of zonules – due to contraction of ciliary muscles Change in curvature of lens - almost no change in posterior surface (6 mm) - anterior surface radius of curvature (from 11 mm to 6 mm)

8. Anterior pole along with iris moves forward - shallowing of anterior chamber in centre Pupillary constriction and convergence of eyes - near triad Choroid moves forward Ora serrata moves by 0.05mm forward with each diopter of accommodation

9. L ens shape change with Accommodation Anterior r =6 mm

10. What triggers Accommodation ?? Image blur Apparent size and distance of object Disparate retinal images Contrast Luminance Chromatic aberration

11. Components of Accommodation

12. Reflex Accommodation The normal involuntary response to blur which maintains a clear image Largest and most important component Automatic adjustment of refractive state to obtain clear retinal image Occurs for small amount of blur, upto 2.00 D, beyond which voluntary effort is required Voluntary A ccommodation

13. Vergence Accommodation Induced due to action of disparity (fusional) Vergence . Second major component of accommodation

14. Proximal Accommodation Due to influence or knowledge of apparent nearness of object Stimulated by targets located within 3m of the individual Tertiary component of accommodation

15. Tonic Accommodation Revealed in absence of blur, disparity, and proximal inputs as well as any voluntary or learned unusual aspects. Reflects baseline neural innervation from the midbrain. In young adults, ranges from 0 to 2 D

16. Measurement of Accommodation A full clinical examination includes assessment of accommodative function in five parameters A mplitude of accommodation L ag of accommodation A ccommodative facility R elative accommodation Accommodation fatigue

17. Amplitude of Accommodation Punctum R emotum - The farthest point at which the objects can be seen clearly - Infinity for e mmetropic eyes Punctum Proximum - The nearest point at which objects can be seen clearly

18. Range of accommodation - Distance between near point and far point Amplitude of accommodation - The dioptric difference between near point and far point (A= P-R) Amplitude of Accommodation

19. Measurement of Amplitude of Accommodation Push up method Minus lens method

20. Push Up Method - T o determine maximum amount of accommodation that eyes are capable of producing individually or together - Done by RAF Rule, Livingstone Binocular Gauge,Prince Rule Measurement of Amplitude of Accommodation

21. Royal Air F orce R ule Wing like support that fits over nose and rests against lower orbital margins Test chart Metal rod 1 st side : divided into cm for NPA 2 nd side : divided into diopter(NPA in D ) 3 rd side : age Prince Rule

22. Procedure: Near visual acuity chart placed on near point rod Direct patient’s attention to 20/20 line of letters on near point card Patient left eye occluded

23. Near point card brought closer to patient ( 2-3 inches per second) Patient instructed to keep the letters as clear as possible and report when it blurs Prompt the patient to clear the target

24. Stop when patient can no longer clear the print within 2 to 3 seconds of viewing Record the dioptric points on the near point rod that corresponds with the blur Procedure repeated for left eye

25. Hofstetter formulae for expected amplitude as a function of age (using the data of Donders , Duane and Kaufman ) Maximum amplitude = 25 - 0.4(age) Probable amplitude = 18.5 - 0.3(age) Minimum amplitude = 15 - 0.25(age) Formula to determine Amplitude of Accommodation

26. Example : For 20 years old patient M inimum AA is given by : 15 – 0.25 x age= 15 – 0.25 x 20 = 10 DS NPA = 1 /10 = 0.1m = 0.1 x 100 cm = 10 cm

27. Accommodation Insufficiency & presbyopia AI PRESBYOPIA Accommodative power is significantly less than the normal physiological limit for the patient’s age Physiological insufficiency of accommodation is normal for age Asthenopic symptoms are more prominent Symptom s of decreased near VA is more prominent

28. Amplitude of accommodation and age The amplitude of accommodation declines throughout life until at about 50 or 60 years of age when it becomes zero

29. Rule of 4’s Amplitude= 4x4- (Age/4 ) Example: Age of 20, Amplitude = 16-20/4 = 11 diopters Amplitude of accommodation and age

30. Anomalies of Accommodation

31. General symptoms: Intermittently blurred vision Eyestrain and/or headache with visual tasks Fatigue/sleepiness with visual tasks Inattentiveness over time

32. Accommodation Insufficiency The accommodative amplitude is distinctly below the lower limit of the expected amplitude in relation to the age of the individual Similar to presbyopia Can result from systemic conditions such as diabetes mellitus, multiple sclerosis, anemia, general physical fatigue, myasthenia gravis, trauma, malnutrition, convalescence from debilitating illnesses and chronic alcoholism

33. Specific symptoms: Blurred vision/eyestrain with NEAR visual tasks Intermittent diplopia due to associated disturbances of convergence

34. Rule out… Causes of Unilateral Accommodation Failure: Congenital unilateral third nerve palsy Transient, post traumatic, accommodation failure associated with traumatic mydriasis Causes of Bilateral Accommodation Failure: Cortical vision impairment Foveal hypoplasia (albinism, aniridia ) Down syndrome Iso-ametropic amblyopia Ectopia lentis Macular degeneration Nanophthalmos Near vision palsy

35. Treatment: Spectacle correction For near- weakest convex lenses should be prescribed If there is associated convergence insufficiency base out prism may be added to patient comfort In cases with convergence excess full spherical correction should be prescribed

36. Vision Therapy: To stimulate accommodation mono- ocularly Small print targets that are slowly moved CLOSER to the eye Reading print through MINUS lenses (gradually increasing the power) using “Monocular minus lens rock” Monocular lens flippers Monocular minus lens clear/blur/clear (for fine voluntary control) Binocular lens flippers

37. Ill-sustained Accommodation Initial stage of true insufficiency Range is normal During prolonged near work, accommodative power weakens, the near point gradually recedes and vision becomes blurred

38. Inertia of Accommodation Rare condition Difficulty in altering the range of accommodation Requires time and effort to focus a near object after looking into distance Treatment: Correction of refractive error Accommodative Exercises

39. Paralysis of Accommodation Causes: Drug induced cycloplegia –atropine , homatropine Internal opthalmoplegia [paralysis of cilliary muscle & sphincter pupillae ] Neuritis associated with chronic alcoholism, diabetes CNS infections Head Injury Specific Symptoms: Blurring of near vision Photophobia [glare]

40. Treatment: Self recovery occurs in drug induced paralysis Dark glasses are effective in reducing the glare Convex lenses for near vision may be prescribed

41. Treatment: Accommodation Excess Prescribing lenses Distance lens prescription Added plus lenses are not usually accepted for near work Vision Therapy: To relax accommodation monocularly Small print targets slowly moved AWAY from the eye Reading print through PLUS lenses (gradually increasing the power)

42. Spasm of Accommodation Abnormally excessive accommodation which is out of voluntary control of the individual Causes: Drug induced spasm after use of strong miotics Spasm of near reflex

43. Specific symptoms: Blurred vision at DISTANCE after performing near visual tasks Treatment: Relaxation of ciliary muscle: the most effective method of treatment is complete ciliary paralysis with atropine

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