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Accommodation by Surendra

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Accommodation by Surendra

  1. 1. Surendra Shah SGT University
  2. 2. 2 Accommodation is the process by which the crystalline lens changes its power. Definition
  3. 3. 3 Increases the total dioptric power of the eye Moves the ocular image anteriorly Allows the eye to keep a clear image on the retina when closer objects are viewed Allows hyperopes to clear what would otherwise be a blurred retinal image  Their image of distant objects is behind the retina when the eye is unaccommodated Accommodation
  4. 4. 4 Accommodation Near Object -- No Accommodation Object at Infinity
  5. 5. Association with Convergence Pupillary Miosis Near triad AccommodationAccommodation Accommodation
  6. 6. 6 Training (somewhat dependent) Age (highly dependent) The amount of accommodation available depends upon
  7. 7. 7  Accommodation is mediated by parasympathetic stimulation of the ciliary body under the innervation of the IIIrd cranial or oculomotor nerve, arising in the midbrain.  In the absence of a definite visual stimulus, a low degree of neural activity gives rise to some ciliary muscle tonus -- this creates the resting state known as tonic accommodation or the resting state. Physiology of Accommodation
  8. 8. 9 Lens Shape Change with Accommodation
  9. 9. Effective Stimuli for Accommodation Retinal Blur • Accommodation occurs to improve the contrast and clarity of the retinal image :optical reflex accommodation
  10. 10. Components of Accommodation 1. Tonic Accommodation 2. Convergence Accommodation 3. Proximal Accommodation 4. Reflex Accommodation 5. Voluntary Accommodation
  11. 11. 12  The resting state of accommodation  The amount of accommodation present in the absence of a stimulus.  In youth this is about 1 to 2 D, reducing with age as the amount of accommodation reduces. Tonic accommodation
  12. 12. 13 The amount of accommodation stimulated by the convergence of the eyes on a near object.  With two eyes there is a convergence- induced response which helps to maintain the accuracy of accommodation Convergence Accommodation
  13. 13. 14  The reaction time for convergence is about 0.2 s, almost twice as fast as that for accommodation  accommodation lags behind and takes its cue from convergence. Lag Time
  14. 14. Measurement AC/A  Calculation method (Heterophoria method)  AC/A = PD + n+ d / D  Where, D = testing distance  Gradient method  AC/A = n+ d / D  Where, D = Power of the lens  Graphical method  Normal Value: 4/1 t0 6/1
  15. 15. 17  The amount of accommodation induced by the subject's awareness of the proximity of an object.  In instruments such as autorefractors, it interferes with the objective measurement of refractive error  Autorefractors tend to give readings  overcorrections for myopia  undercorrections for hyperopia. Proximal accommodation
  16. 16. 18  An example of this is the viewfinder on a camera  To compensate for this, minus lenses are sometimes incorporated into camera sights  This instrument myopia is also the cause of too much minus in prescriptions determined by some autorefractors. Proximal Accommodation
  17. 17. 19  Accommodation can also occur in response to the awareness of nearness to an object  This is often referred to as proximal accommodation  Awareness of proximity is responsible for the increases in accommodation that often occur when looking into instruments held close to the eye Proximal Accommodation
  18. 18. 20 The normal involuntary response to blur which maintains a clear image Reflex accommodation
  19. 19. 22 A full clinical examination  includes assessment of accommodative function in four parameters amplitude of accommodation lag of accommodation accommodative facility relative accommodation Clinical Measurement of Accommodation
  20. 20. 24  Defn :  The maximum amount by which the eye can change its power is known as the amplitude of accommodation.  The dioptric difference between the punctum proximum and the punctum remotum.  e.g:  if the far point is 50 cm in front of the spectacle plane and the punctum proximum is 8 cm in front of it, the amplitude is:  Ans:  AA = (1/kpr )-(1/kpp ) = (1/-0.5m)-(1/-0.08m) = +10.5D Amplitude of Accommodation
  21. 21. 25  The punctum proximum is the nearest point at which we can achieve clear vision.  It is the object point at which the eye is fully accommodated, using its full amplitude of accommodation.  ?Punctum remotum??? Punctum Proximum
  22. 22. 27 The amplitude of accommodation declines throughout life until at about 50 or 60 years of age the amplitude of accommodation becomes zero  (A nonzero measurement after these ages based on the subject's report of blur is typical because of the depth of field of the eye.) Amplitude of Accommodation
  23. 23. 28 Accommodation vs. Age
  24. 24. 29 Amplitude of Accommodation vs. Age
  25. 25. 30  Assuming a linear decline in amplitude, Hofstetter formulas 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)
  26. 26. 31  Lag of accommodation can be assessed clinically  Dynamic retinoscopy  near bichrome test  the near cross cylinder test  Normal Lag: +0.50 or +0.75 diopters  High Lag: +1.00 diopters or higher  Decreased Lag: +0.25 diopters or less Lag of Accommodation
  27. 27. Anomalies of Accommodation  Accommodation Insufficiency  Accommodation Infacility  Accommodative Fatigue  Paralysis of Accommodation  Latent Hyperopia  Accommodative Spam (Pseudomyopia)  Presbyopia (? Physiological conditions)
  28. 28. Accommodation Insufficiency  Accommodative response is significantly less than accommodative stimulus  Signs &Symptoms:  Blurred vision, difficulty reading, irritability, poor concentration  Asthenopia at end of day  Excessive convergence might occur in attempting to accommodate – AC/A relationship  Amplitude of Accommodation is less than expected for patient’s age  Usually fail the flipper test (+/- 2.00D)  Positive Relative Accommodation (PRA) is less than –1.50D
  29. 29.  Feature  Inability to clear minus lens  Causes: ? Functional etiology (Careful history taking)  Drug: alcohol, Cycloplegics, CNS stimulants, marijuana, antihistamines  Ocular diseases: Glaucoma, Iris sphincter tear, trauma, Adie’s syndrome, Horner syndrome, Herpes Zoster  Diabetes, sinusitis, multiple sclerosis, dental caries, tonsillitis, Wilson disease  Arsenic/ lead poisoning,
  30. 30. Accommodation Insufficiency  Management:  Correct refractive error : small hyperopia/ astigmatism  Near add: NRA + PRA/ 2 or accommodative lag value  Vision training  Lens rock with +/- flippers  Hart chart rock  Brock string (Jump vergence)
  31. 31. Flipper’s lens Tests patients ability to vary blur- driven accommodation response rapidly. Line of fine print at 40cm distance Quantified in terms of no. of cycles completed in 60 seconds. Full 60 sec., should always been used. Normal value will be 18 – 20 cycles/ minute.
  33. 33. HART charts HC therapy uses a change in fixation distance as the stimulus to accommodation. Block of 100 letters (10 x 10) Contains larger & smaller versions of letters. Used for both push-up and facility.
  34. 34. HART - charts
  35. 35. Brock’s string /Push – up method
  36. 36. Accommodation Infacility  Slow or difficult accommodative response to dioptric change in stimulus  Signs & Symptoms  Poor ease in change of accommodation stimulus  Pts c/o distance blurring after prolonged near work and/or near blur after prolonged distance work  Fail flipper test (+/- 2.00D)  Might have normal AA  Abnormal Both PRA or NRA  Feature:  Fail miserably when trying to clear plus & minus lenses (flippers) > 8 cycles per minute  Etiology: ?? Functional
  37. 37. Accommodation Infacility Spectacle correction Near add: Due to Low NRA & PRA won’t benefit Vision therapy: Flippers Hart chart rock Brock string (Jump vergence)
  38. 38. Accommodative Fatigue Inability of the eye to adequately sustain sufficient accommodation over an extended time period. Signs &Symptoms:  Blurred vision after prolonged near work  Accommodative system fails to sustain accommodation  Like Acc. Insufficiency  except Amp.Acc. is normal
  39. 39. Amp. Acc. on repeated testing reduces Usually fails flipper test (+/- 2.00D) Decreased PRA Feature: Difficulty to clear plus lenses Etiology: ????? Functional
  40. 40. Accommodative Fatigue Management Spectacle correction Near add:  Benefit with plus lens Vision therapy: Flippers Hart chart rock Brock string (Jump vergence)
  41. 41. Paralysis of accommodation  Non- presbyopic patient  loses accommodation monocularly or binocularly  Complain : blur  Paralysis can be caused by many factors:  Trauma, toxicity, Adie’s Pupil, neuropathy, drugs (cycloplegic agents)  Etiology should be known if possible
  42. 42. Latent Hyperopia  Portion of total hyperopia compensated by accommodation (tonicity of the ciliary muscle)  Symptoms:  Inability to do near work for long (focusing problem)  Asthenopia  Need to do cyclorefraction  Correct refractive error : small hyperopia/ astigmatism
  43. 43. Accommodative Spam (Pseudomyopia)  Due to ciliary muscle spasm, inability of the eye to relax accommodation Results in pseudomyopia  Signs & Symptoms  Eyes over-accommodates for a stimulus  Constant parasympathetic innervations of the near reflex  Usually not associated with organic disease  Etiology might be psychogenic  Distance VA can also be impaired  Pseudomyopia  Poor response to all the tests which need to relax accommodation (unable to clear plus lens)
  44. 44. Accommodative Spam (Pseudomyopia)  Management:  Spectacle correction: cycloplegic refraction  Correction of small hyperopia/ astigmatism  Minus lens for distance blur will compound the problem  “ Push the Plus & minimum minus lens “ for distance  Vision therapy:  General relaxation therapy to reduce excessive accommodative effort & improving accommodative control  Similar as for other accommodative disorders
  45. 45. 55  The blur during near vision resulting from the normal decrease in amplitude of accommodation with age is known as presbyopia  Presbyopia is sometimes quantitatively defined as an amplitude of accommodation less than 5 D, which is the point at which many patients become symptomatic.  This usually occurs at about 40 or 45 years of age Presbyopia
  46. 46. 56 Presbyopia that has advanced to the point that the ability to accommodate is completely absent is known as absolute presbyopia Absolute presbyopia is reached between 50 and 60 years of age Absolute Presbyopia
  47. 47. 57 The treatment for presbyopia is the addition of plus power for use when viewing near objects This is usually in the form of reading glasses, bifocal spectacles, or multifocal spectacle lenses. Treatment for Presbyopia