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  1. 1. Theories of Accommodation and it’s Anomalies Presenter: Dr. Rujuta Gore Moderator: Dr. Atul Seth
  2. 2.  A dioptric change in the power of the eye to see clearly
  3. 3. Relaxation Theory of Helmholtz  Proposed by Thomas Young  Elaborated by Hermann von Helmholtz  Most widely accepted
  4. 4. Relaxation Theory of Helmholtz eye is at rest and focused for distance ciliary muscle is relaxed eye makes an effort to focus on a near object ciliary muscle contracts bulk of the anterior ciliary body moves forward release in tension on the zonular fibres elastic capsule moulds the lens into a spherical form
  5. 5. Relaxation Theory of Helmholtz  Increase in surface curvatures causes an increase in optical power of the lens and therefore an increase in power of the eye
  6. 6. Helmholtz’s Theory: Disaccommodation ciliary muscle contraction ceases posterior zonular fibres pull the ciliary muscle backward increases tension on the zonular fibres increase in lens diameter, decrease in lens thickness and a flattening of the anterior and posterior lens surface curvatures decrease in optical power
  7. 7. Shortcomings of Helmholtz’s Theory  Since the equatorial diameter increases with age, zonules should relax, and power of the crystalline lens should increase.  Lens should become unstable
  8. 8. Schachar’s Theory  Proposed by Ronald Schachar  Alternative theory  Contradicts the classical Helmholtz’s mechanism
  9. 9. Schachar’s Theory ciliary muscle contracts equatorial zonular tension is increased anterior and posterior zonules are simultaneously relaxed central surfaces of the lens steepen peripheral surfaces of the lens flatten
  10. 10. Helmholtz’s and Schachar’s Theory
  11. 11. Shortcomings of Schachar’s Theory  Based on his theory, Schachar introduced a new surgery in 1992 i.e. the use of scleral expansion bands to increase the distance between the lens equator and ciliary muscle.  Poor results of this surgery challenged the validity of his theory
  12. 12. Catenary (hydraulic suspension) Theory  Proposed by Coleman DJ in 1970  Demonstrated in 2001  Explains the precise anatomical reproducible shape of the lens in accommodated state  Assumption : the lens, zonule and anterior vitreous comprise a diaphragm between the anterior and vitreous chambers of the eye
  13. 13. Catenary (hydraulic suspension) Theory  What is “catenary”?
  14. 14. Catenary (hydraulic suspension) Theory ciliary muscle contracts initiates a pressure gradient between the vitreous and aqueous compartments anterior capsule and the zonule form a trampoline shape or hammock shaped surface steep radius of curvature in the center of the lens with slight flattening of the peripheral anterior lens
  15. 15. Clinical Assessment  Reading progressively smaller letters at near  NPA using RAF rule  Relative positive accommodation using minus lenses  Accommodative flipper test using paired +/– lenses  Dynamic Retinoscopy  Dynamic Distant Direct Ophthalmoscopy
  16. 16.  TERMS TO REMEMBER:  Range of Accommodation  Amplitude of Accommodation  Relative Amplitude of Accommodation  Lead  Lag  Facility of Accommodation
  17. 17.  Range of Accommodation: The distance between the far point and near point ie the distance over which accommodation is effective  Amplitude of Accommodation: The difference between dioptric power needed to focus at far point (at rest) and at near point (fully accommodated)
  18. 18.  Relative amplitude of accommodation: The total amount of accommodation which the eye can exert while the convergence of the eyes is fixed  It can be positive (using concave lenses until the image blurs). This is called positive relative accommodation (PRA).  It can be negative (using convex lenses until the image blurs). This is negative relative accommodation (NRA)
  19. 19.  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
  20. 20. Clinical Assessment  Measurement of NPA:  It is the closest point at which an object can be seen clearly  Also called “near point” or “punctum proximum”  Measured with the RAF rule
  21. 21. DDDO  An emmetropic eye has “with” movement on retinoscopy and “superior” crescent on DDDO while 1D myopia (due to accommodation) shows “no movement” on retinoscopy and disappearance of superior crescent on DDDO  DDDO is an easier test than DR  Location of bright crescent moving from top to the bottom of the pupil is probably easier to recognize[Fig. 5] than change in the movement of the retinoscopy reflex (“with” movement to the “against” movement), more so when the pupils are dilated
  22. 22. Anomalies of Accommodation  General symptoms:  Problems are longstanding  Intermittently blurred vision  Eyestrain and/or headache with visual tasks  Fatigue/sleepiness with visual tasks  Inattentiveness over time
  23. 23. Anomalies of Accommodation Classification Decreased Accommodation Insufficiency Ill-Sustained Accommodation Inertia Paralysis Increased Accommodation Excess Spasm
  24. 24. 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
  25. 25. Accommodation Insufficiency  Specific symptoms:  Blurred vision/eyestrain with NEAR visual tasks  Intermittent diplopia due to associated disturbances of convergence  Examination findings  Reduced amplitude of accommodation  Higher than normal lag of accommodation  Difficulty clearing -2.00 D lenses on monocular and binocular accommodative facility testing  PRA (positive relative accommodation) lower than -1.50
  26. 26.  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 Rule out…
  27. 27. Treatment: Accommodation Insufficiency  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  ACCOMMODATION TEST-CARD EXERCISE
  28. 28.  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 Treatment: Accommodation Insufficiency
  29. 29. 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
  30. 30. 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
  31. 31. 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]
  32. 32. Treatment: Paralysis of Accommodation  Self recovery occurs in drug induced paralysis  Dark glasses are effective in reducing the glare  Convex lenses for near vision may be prescribed
  33. 33. Accommodative Excess
  34. 34. Treatment: Accommodative 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)
  35. 35. 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
  36. 36. Spasm of Accommodation  Specific symptoms:  Blurred vision at DISTANCE after performing near visual tasks  Examination findings:  Lead of accommodation  Difficulty clearing +2.00 D. lenses on monocular and binocular accommodative facility testing  NRA lower than +1.50
  37. 37. Treatment: Spasm of Accommodation  Relaxation of ciliary muscle: the most effective method of treatment is complete ciliary paralysis with atropine
  38. 38. Accommodative Infacility  Specific symptoms:  Blurred vision when CHANGING focus far → near and near → far  Examination findings:  Difficulty clearing both +2.00 and -2.00 D. lenses on monocular and binocular accommodative facility testing  PRA lower than -1.50 and NRA lower than +1.50
  39. 39. Treatment: Accommodative Infacility  Vision Therapy: to stimulate/relax accommodation monocularly  Alternately focusing on small print targets at near and far (with the near target slowly moved closer to the eye).  Reading near print through alternating PLUS and MINUS lenses (gradually increasing the power)

Notas do Editor

  • Also called capsular theory
  • Equator is getting nearer to the ciliary muscle
  • Because of the increased equatorial zonular tension on the lens during accommodation, the stress on the lens capsule is increased and the lens remains stable.
  • As the equatorial diameter of the lens continuously increases over life, perilenticular space is reduced and ciliary muscle contraction can no longer tense the zonules and expand the lens coronally. This results in presbyopia.
  • Hammock shaped surface is reproducible depending on the circular dimensions, i.e. the diameter of the ciliary body.
    Presbyopia occurs due to increasing lens volume with age, which results in reduced response of anterior lens to vitreous pressure gradient
  • When the eye is at rest, we call the refraction as static. When the refraction is alteres by exercise of accommodation, it is called as dynamic.
  • Collectively called as asthenopia
  • the accommodation test card consists of a black vertical line draw on a white card . Patient holds it at considerable distance from eyes & then brings it closer until the line appears blurred & indistinct . By repeating this he should be encouraged to attempt to bring his near point as close as possible
  • Causes and treatment are same as for Accommodation insufficiency
  • Spasm of near reflex is a clinical syndrome often seen in tense or disturbed individuals who present with excessive accommodation, excessive convergence & miotics