ACCOMODATION AND ITS ANOMALIES PRESENTED BY

1. ACCOMODATION
AND ITS ANOMALIES
DR KRIPESH LAMICHHANE
2ND YEAR RESIDENT
CMC

2. INTRODUCTION
 As we know in an emmetropic eye, parallel rays of light coming from the
infinity are brought to focus on the retina, with accommodation being at
rest.
 However our eyes have been provided by a unique mechanism by which
we can even focus the diverging rays coming from a near object on the
retina in a bid to see clearly.
 This mechanism is called accommodation.

3. Components of near reflex are:
1. Accomodation, i.e., increase in curvature of anterior surface of the
crystalline lens, leading to increase in focusing power of the lens.
 At rest, the radius of curvature of anterior surface if the lens is 10 mm and
that of the posterior surface is 6 mm.
 During accommodation the curvature of the porsterior surface remains the
same but that of anterior surface changes.
 In strong accommodation, curvature of anterior surface also becomes
6mm.

4. 2. Constriction of pupil: leading to sharp focus. It occurs due to reflex
contraction of sphincter pupillae muscle.
3. Convergence of eyeball: leading to focusing of both eyes on the near
object. It occurs due to contraction of the medial rectus.

5. MECHANISM OF ACCOMODATION
 According to Von Helmholtz’s capsular theory the process of accommodation
is achieved by a change in the shape of lens.
 When eye is at rest (unaccommodated), the ciliary ring is large and keeps the
zonules tense. Because of zonular tension the lens is kept compressed (flat) by
the capsule.
 Contraction of the ciliary muscle causes the ciliary ring to shorten and thus
releases zonular tension on the lens capsule.
 This allows the elastic capsule to act unrestrained to deform the lens
substance.
 The lens then alters its shape to become more convex or conoidal (to be more
precise).
 The lens assumes conoidal shape due to configuration of the anterior lens
capsule which is thinner at the centre and thicker at the periphery.

7. OCULAR CHANGES IN
ACCOMODATION
 Slackening of zonules- due to contraction of ciliary muscles
 Changes in curvature of lens:
 Almost no change in posterior surface (6mm)
 Anterior surface radius of curvature ( decreases from 11 mm to 6 mm)

9.  Anterior pole along with iris moves forward
 Shallowing of anterior chamber in centre
 Pupillary constriction and convergence of eyes
 Near triad
 Choroid moves forward
 Orra serrata moves by 0.05mm forward with each diopter of
accommodation

12. What triggers accommodation??
 Image blur
 Apparent size and distance of object
 Disparate retinal images
 Contrast
 Luminance
 Chromatic abberation

13. Components of accommodation
 Reflex
 Vergence
 Proximal
 Tonic

14. REFLEX ACCOMODATION
 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 2.00D, beyond which voluntary effort
is required.
Voluntary Accommodation

15. Vergence Accomodation
 Induced due to action of disparity (fusional) vergence
 Second major component of accommodation

16. 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

17. 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

18. Measurement of Accommodation
 A full clinical examination includes assessment of accommodative function
in five parameters
 Amplitude of accommodation
 Lag of accommodation
 Accommodative facility
 Relative accommodation
 Accommodation fatigue

19. FAR POINT AND NEAR POINT
 The nearest point at which small objects can be seen clearly is called near
point or punctum proximum.
 The distant(farthest) point is called far point or punctum remotum.
 Far point and near point of the eye:
These vary with the static refraction of the eye as shown below:
 In an emmetropic eye far point is infinity and near point varies with age.
 In hypermetropic eye far point is virtual and lies behind the eye.
 In myopic eye, it is real and lies in front of the eye.

20. RANGE AND AMPLITUDE OF
ACCOMODATION
 Range of accommodation: The distance between the near point and the far
point is called the range of accommodation:
 Amplitude of accommodation: the difference between the dioptric power
needed to focus at near point(P) and far point (R) is called amplitude of
accommodation (A). Thus A=P-R
 Amplitude of accommodation and thus the near point of vision(punctum
proximum) vary with age.

22. Measurement of Amplitude of
Accommodation
 Push up method
 Minus lens method

23. Measurement of Amplitude of
Accommodation
 Push up method
 To determine maximum amount of accommodation that eyes are capable
of producing individually or together
 Done by RAF rule, Livingstone Binocular Gauge, Prince Rule

25. 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 eye occluded

26.  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

27.  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

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

29.  Example:
 For 20 yrs old patient
 Minimum AA is given by: 15-0.25 x 20= 10 DS
 NPA= 1/10=0.1 m= 10 cm

32. Amplitude of Accommodation and
Age
 Rule of 4 A’s
 Amplitude= 4 x 4- (Age/4)
Example:
Age of 20,
Amplitude = 16- 20/4 = 11 diopters

34. General Symptoms
 Intermittently blurred vision
 Eyestrain and/or headache with visual tasks
 Fatigue/sleepiness with visual tasks
 Inattentiveness over time

35. PRESBYOPIA
 Is not an error of refraction but a condition of physiological insufficiency of
accommodation leading to a progressive fall in near vision

36. pathophysiology
 As we know in an emmetropic eye far point is infinity and near point varies
with age (being about 7 cm at age of 10 years, 25 cm at the age of 40
years and 33 cm at the age of 45 years).
 Therefore at the age of 10 years, amplitude of accommodation(A)=
100/7(diopteric power needed to see clearly at any point)-
1/infinity(diopteric power needed to see clearly at far point)= 14 diopters
 Similaryly at age 40=100/25-1/infinity= 4 diopters
 Since we usually keep the book at about 25 cm, so we can read
comfortably up to the age of 40 years.

37.  Causes: decrease in the accommodative power of crystalline lens with increasing age,
leading to presbyopia, occurs due to:
1. Age related changes in the lens which include:
Decrease in elasticity of lens capsule
Progressive increase in size and hardness of lens substance which is less easily moulded.
2. Age related decline in ciliary muscle power may also contribute in causation of
presbyopia.
Causes of premature presbyopia are:
Uncorrected hypermetropia
Premature sclerosis of the crystalline lens
General debility causing presenile weakness of ciliary muscle
Chronic simple glaucoma

38. symptoms
 Difficulty in near vision
 Asthenopic symptoms : due to fatigue of ciliary muscle
 Intermittent diplopia

39. TREATMENT
 Optical treatment: convex glass for near work
 Surgical treatment:
1. Cornea based procedures: monovision conductive keratoplasty (CK)
2. Monovision LASIK
3. Presbyopic bifocal LASIK AND LASIK-PARM( LASIK by Presbyopia Avalos
Rozakis Method)
4. Presbyopic multifocal LASIK
5. Presbyond laser blended vision
6. Corneal inlays for presbyopia

40.  Lens based procedures:
1. Trifocal IOL
2. Monovision with intraocular lenses
 Sclera based procedures:
1. Anterior ciliary sclerotomy
2. Scleral spacing procedures and scleral ablation
3. Scleral expansion

41. INSUFFICIENCY OF ACCOMMODATION
 When Accommodative power is significantly less than the normal
physiological limits.
 Therefore it should not be confused with presbyopia in which the
physiological insufficiency of accommodation is normal for the patient’s
age.
 So it can be labelled as pathological insufficiency of accommodation.

42.  Causes:
1. Premature sclerosis of lens
2. Weakness of ciliary muscle due to systemic causes of muscle fatigue such
as debiliating illness, anemia, toxaemia, malnutrition, diabetes mellitus,
pregnancy, stress and so on
3. Weakness of ciliary muscle associated with primary open angle glaucoma
4. Cyclitis

44. TREATMENT
 Near vision spectacles in the form of weakest convex lens which allows
adequate vision should be given till the power of accommodation
improves
 If there is associated convergence insufficiency base out prism may be
added to patient comfort
 Accommodation exercises help in recovery, if underlying debility has
passed.

45.  Vision therapy: to stimulate accommodation monocularly
 Small print targets that are slowly moved closer to the ye
 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

46. PARALYSIS OF ACCOMODATION
 Also known as cycloplegia refers to complete absence of accommodation
 Causes:
1. Drug induced cycloplegia
2. Paralytic internal ophthalmoplegia (paralysis of ciliary muscle and
sphincter pupillae)- seen in neuritis associated with diphtheria, syphilis,
diabetes, alcoholism, cerebral or meningeal diseases.
3. Paralysis of accommodation as a component of complete third nerve
paralysis may occur due to intracranial or orbital causes.

47. Clinical features
 Blurring of vision
 Photophobia
 Abnormal receding of near point and markedly decreased range of
accommodation

48. Treatment
 Self recovery occurs in drug induced cycloplegia and in diphtheria cases
 Dark glasses
 Convex lenses for near vision

49. Spasm of Accommodation
 Exertion of abnormally excessive accommodation
 Also known as cyclotonia

50. causes
 Drug induced spasm of accommodation after use of strong miotics such as
echothiophate and DFP(Diisopropylflourophosphate)
 Spontaneous spasm of accommodation- in children who attempt to
compensate for a refractive anomaly that impairs their vision (when eyes
are used for excessive near work in bad illumination, bad reading position,
lowered vitality, state of neurosis, mental stress or anxiety)

51. Clinical features
 Sudden defective vision due to induced myopia (pseudomyopia)
 Asthenopic symptoms

52. Diagnosis
 Made with refraction under atropine cycloplegia

53. Treatment
 Relaxation of ciliary muscle by atropine for few weeks and prohibition of
near work
 Correction of associated causative factors
 Assurance and psychotherapy

54. ILL SUSTAINED ACCOMODATION
 Initial stage of true insufficiency
 Range is normal
 During prolonged near work, accommodative power weakens, the near
point gradually recedes and vision becomes blurred

55. INERTIA OF ACCOMODATION
 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

56. Accomodation Excess : TREATMENT
 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)

59.  THANK YOU