In 1939, Chavasse attributed the development of amblyopia and facultative suppression to the process of adaptive inhibition in the face of dissociatio

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1 Amblyopia History of amblyopia Le Cat (1713) is credited with providing the first accurate clinical description of human amblyopia. However, credit for first describing any treatment for amblyopia is given to George Louis Leclerc, Conte De Buffon ( ) Buffon was the first to realize the two most important elements in amblyopia therapy: occlusion and full optical correction

2 In 1939, Chavasse attributed the development of amblyopia and facultative suppression to the process of adaptive inhibition in the face of dissociation. This is known as the theory of amblyopia of arrest versus amblyopia of extinction.

3 Chavasse divided amblyopia into two types: Amblyopia of arrest there is a cessation of development of vision in the involved eye that must occur before the age of 6 years. Chavasse felt that 20/20 vision is firmly established by age 6 years and amblyopia of arrest is considered irreversible. Amblyopia extinction The amblyopia could be improved, but only up to the best vision that was obtained before the onset of the anomalous visual experience.

4 Dobson and Teller ( 1978) More recent objective methods have demonstrated 20/20 VA can be obtainable by about 6 to 12 months of age with certain testing procedures. Amblyopia of arrest can only exist when the anomalous visual experience occurs before 6 months or so. consequently, the majority of amblyopia is of the extinction type and therefore potentially reversible.

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7 Example 1. Onset of abnormal visual experience is at age of 1 year 2. Best VA at age 1 year: Chavasse : 20/120 Dobson and Teller: 20/20 3. Best VA now( after age 6 years and without previous treatment) : 20/200

8 Chavasse ( 1939) 20/200 to 20/120 = deficit due to extinction and therefore fully reversible 20/120 to 20/20 = deficit due to arrest and therefore nonreversible Dobson and Teller ( 1978) 20/200 to 20/20 = deficit due to extinction and therefore fully reversible

9 Definition Amblyopia is an unilaterally or bilaterally decrease of visual form sense for which no obvious structural or pathologic causes can be detected, and which is not overcome by correction of the refractive error.

10 The problem with the definition description is the no structural causes is depended on the depth of the clinical investigation. Another problem is that many cases of amblyopia are cured simply by wearing spectacles, though over a period of time. This is why recent studies have changed the clause to a visual loss resulting from an impediment or disturbance to the normal development of vision, and not directly correctable with glasses

11 Amblyopia develops in infants and very young children, beginning only during the first 6 years old. The most critical period for loss of binocularity and for the development of functional amblyopia is the first 18 months of life ( Levi 1994). Once established, it can persist for life. If treat early, its effects are completely or nearly reversible. Different visual functions have different sensitive periods: the sensitive periods for cortical visual functions are longer than for retinal functions.

12 The visual acuity of amblyopia ranges from slightly less than normal ( 20/25) to functional blind ( less than 20/200). Light perception is always maintained. There are many criterions to define amblyopia acuity. Amblyopia represents a syndrome of deficits, not just decrease of visual acuity. The depressing are including other ocular functions such as ocular motility, accommodation, contrast sensitivity, and spatial judgment.

13 The low spatial contrast sensitivity is close to normal but there is a marked loss at high spatial frequency. This loss increases with the severity of the amblyopia and does not result from optical factors, unsteady fixational eye movements or eccentric fixation( Flynn 1991). Intermediate spatial frequency is less affected than high contrast VA ( Moseley et al 2006).

14 New definition of amblyopia Unilateral ( or infrequently bilateral) condition in which the best corrected visual acuity is poorer than 20/20 in the absence of any obvious structural or pathologic anomalies but with one or more of the following conditions occurring before the age of 6 years

15 Continue 1. Amblyogenic anisometropia 2. Constant uniteral esotropia or exotropia 3. Amblyogenic bilateral isometropia 4. Amblyogenic unilateral or bilateral astigmatism 5. Image degradation

16 Prevalence of amblyopia Amblyopia is common, but it s prevalence has been difficult to assess due to: Differences in criteria Various populations Type of visual acuity test Omission of successfully treated or prevented amblyopia Incomplete examination

17 Preschool and school age children 1% to 4.8% Ophthalmic patients seeking eye care 1.7% to 5.6% Military personnel 1% to 4%

18 Incidence of amblyopia A higher incidence has been associated with prematurity, low birth weight, retinopathy of prematurity, cerebral palsy, and metal retardation. Maternal smoking and use of drugs or alcohol during pregnancy are also in high risk. Data in various sub-populations is generally not available. No difference between males and females. The relative importance of environment and genetic factors in the development of amblyopia is also unclear.

19 Etiology The sensory obstacles in the early life Retinal image degradation Cataract, lid closure, high uncorrected refractive errors Binocular mis-registration Strabismus The factors are sufficient but not necessary to produce amblyopia

20 The role of visual experience in the development of visual function Disruption of binocular input completely disrupts the pattern of cortical excitatory binocular interaction Monocular deprivation has a dramatic effect on the anatomy, physiology, and function of the striate cortex

21 The physiologic consequences of deprivation are more or less confined to the striate cortex The effects of abnormal visual experience occur only during a sensitive period early in life The physiologic consequences of deprivation can be reversed during a critical period early in life

22 Classification All amblyopia was consider either organic, or functional amblyopia. Some contend that amblyopia should be limited to functional etiologies. Organic can not truly be amblyopia because of its structural defects or the impairment of visual pathway, so that medical treatment can be considered.

23 Organic amblyopia Organic amblyopia occurs when the components of visual pathway fail to develop because of any subtle retinal or central nervous system lesion,or undetectable lesion because of metabolic or toxic disturbance. Organic amblyopia includes nutritional, toxic, retinal eye disease, and idiopathic or congenital amblopia.

24 Functional amblyopia Reduced vision was due to physical obstacles such as corneal and lens opacities, as well as strabismus due to suppression of the retinal image in the deviated eye strabismic amblyopia anisometropic amblyopia isoametropic amblyopia image degradation amblyopia Psychogenic amblyopia

25 Psychogenic amblyopia The visual loss is of emotional or psychologic rather than physiologic origin. The amblyopia is characterized by reducing visual acuity for anxiety or emotional repression. The symptoms are not under voluntary control. The diagnosis is made by exclusion of organic pathology and sensory problems. Unilateral visual loss is very rare. Direct to others questions, nearly always reveals additional symptoms such as headache, periorbital pain, photophobia, and sometimes diplopia.

26 Strabismic amblyopia Strabismic amblyopia is associated with an early-onset ( before age 7 years or so), constant, unilateral deviation at distance and at near. The cause is an active cortical inhibition from the fovea of the deviated eye. ( diplopia and confusion)

27 When mention about strabismic amblyopia, primary esotropia and not exotropia typically is associated with amblyopia. Under most condition, exotropia presents as an intermittent and/or alternating deviation rather than a constant unilateral deviation

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30 If a patient presents with an exotropia and reduced unilateral VA in the absence of anisometropia or a history of retinal image degradation, the clinician should suspect organic amblyopia. Remember, there may be a functional amblyopia superimposed over the organic amblyopia, with the cause of the functional amblyopia being the secondary exotropia.

31 Anisometropic amblyopia Anisometropia is frequently considered to be the most common cause of amblyopia. This has been found to occur twice as frequently as strabismic amblyopia. (Unfortunately, fixation status was not tested. Therefore, microtropia with anisometropia would be classified as anisometropic amblyopia ) Flynn and Cassady (1978) analyzed 544 amblyopes, 48% were strabismic, 32% were strabismic and anisometropic, and 20% were purely anisometropic.

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33 A population based study ( Attebo et al 1998) found that the relative prevalence of different types of amblyopia is anisometropic 50%, strabismic 19%, mixed strabismic and anisometropic 27%, and visual deprivation 4%. Amblyopia is more likely to be present in the left eye, and this asymmetry is exaggerated for anisometropia ( Woodruff et al 1994)

34 Coexist of strabismic and anisometropic amblyopia Although anisometropia was defined as a 1- diopter or greater difference between eyes. However, significant amblyogenic anisometrpia is different for myopia and hyperopia. For example: OD plano 20/20 OS sph. 20/100 with left esotropia This patient should be categorized under strabismic amblyopia, since the myopic anisometropia is probably not a significant amblyogenic factor.

35 There exists a controversy as to how one categorizes a patient having both significant anisometropia and unilateral constant strabismus, example: Patients with greater than 5 diopters of anisometropia, over two-thirds had amblyopia, a quarter of whom also had strabismus Patients with less than 2 diopters of anisometropia, about 20 % had amblyopia and only 1 % had a strabismus

36 There is some evidence that emmetropization depends on normal visual experience. In amblyopia, it was found that the refractive error developed at a different rate in the amblyopic eye than in the dominant eye, with the dominant eyes becoming more myopic while the amblyopic eyes stayed the same or became more hyperopic.(nastri et al 1984)

37 Incidence and depth of amblyopia may be dependent on the degree and type of anisometropic refractive error The incidence of amblyopia was lower in myopic than in hyperopia Myopic anisometropia occurs more frequently in the general population than does hyperopic anisometropia

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39 Strabismic amblyopia v.s. anisometropic amblyopia The pupillary function of the eye with strabismic amblyopia is subtly different from that of eyes with anisometropic amblyopia. In anisometropic amblyopia, there is either a difference in retinal image clarity ( and contrast) or a difference in retinal image size. In strabismic amblyopia, there is a form dissimilarity of retinal images. Therefore, the suppression mechanism may be very different.

40 Anisometropic amblyopia reduces sensitivity centrally and peripherally, whereas, strabismic amblyopia losses acuity is predominantly restricted to the foveal region.

41 Isometropic Amblyopia Secondary to a significant bilateral refractive error Even when properly corrected, does not immediately result in normal vision Visual acuity usually improves once the corrective lenses have been worn for a period of time A relatively mild vision loss that is amenable to vision therapy

42 Strabismus secondary to the amblyopia is much less likely to occur Esotropia is more likely to occur in lower amounts of bilateral hyperopia and unilateral amblyopia secondary to an accommodative esotropia Strabismus will result if the AC/A ratio is high, the fusional system cannot handle the excessive vergence demand

43 Clinically, isometropic amblyopes typically exhibit VA in the range of 20/30 to 20/70 in each eye when first corrected If VA is not normalized once the proper corrective lenses are worn for a period of time, then VT is indicated

44 Myopes and astigmats show their best acuities through full correction, whereas hyperopes show better acuities when slightly undercorrected For hyperopes, a large exophoric or tropic deviation may become manifest as the full correction is gradually accepted

45 Isometropic amblyopia is generally detected and treated earlier than anisometropic amblyopia The prevalence of isometropic amblyopia is decreasing in countries where early vision care is emphasized

46 The meridional amblyopia does not develop during the first year of life, despite the high incidence of significant astigmatism during the first year of life May have dissimilar critical period timetables

47 It is difficult to determine precisely the prevalence of isometropic amblyopia It appears to be about 0.03% The effects of bilateral loss of clear form vision are not as damaging as asymmetrical visual inputs The depth of isometropic amblyopia and its resistance to therapy is less High degrees of myopia are frequently associated with retinal thinning and macular pigment abnormalities

48 Image degradation Secondary to the obstruction of sight that prevents the formation of a well focused, high contrast image on the retina Either one or both eyes take place before the 7 year of life for amblyopia to develop Time of onset The extent of the degradation Cataract, corneal opacities, congenital ptosis, and early total occlusion

49 Treatment Early surgery Before 8 weeks of age Total bilateral occlusion between operations on the fellow eye 48 hours or less Early correction of aphakia with extended wear contact lenses Within one week of surgery

50 The importance of early treatment and optical correction The effect of deprivation begins at about 4 months of age, increases rapidly up to 8 months, and the declines gradually over the first decade of life

51 Congenital cataract are often associated with organic ocular diseases: Microphthalmia, coloboma, and optic atriphy The vision is bad Rule out the possibility of functional amblyopia The concept of occlusion amblyopia in human infants is well established Even short periods( less than 1 week) of direct occlusion can result in dramatic changes in monocular acuity and a tradeoff between the two eyes

52 Clinical diagnosis and prognosis of The clinician s task: amblyopia Determine the etiology of the amblyopia Rule out any organic contributions to the VA loss Determine the prognosis and probability for success Organize a comprehensive monocular and binocular treatment strategy

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54 History taking When did the amblyogenic anomaly begin? The later the onset, the better is the prognosis Parents are more likely to recall strabismus rather than anisometropia The anisometropia amblyope is typically first detected during a vision screen If the vision anomaly occurred after age 4 years, the prognosis is excellent Obtaining the results of the earliest vision examination

55 When was treatment initiated? If the uncorrected anomaly has existed for less than 1 year, the prognosis for success is much better There is no drastic difference in prognosis once the non-treated amblyogenic anomaly has existed for greater than 5 years

56 What did the treatment consist of and how successful was it? An amblyope left without either stereopsis or alternation of fixation after treatment is to demonstrate some regression in visual function, especially VA

57 What was the extent of compliance? Need to fully complied and monitored Any history of trauma? Is there a family history? Any diplopia? If yes, suggests recent onset or not very severe Is patient or parent motivated? Without motivation, there will be little or no success

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59 Visual acuity Contour interaction(crowding phenomenon) Contour interaction does not begin at greater than one letter diameter separation The effect is approximately equal at threshold visual acuity levels for both normal and amblyopic eyes

60 The amblyopic eye resolve a few letters per line with no clear cutoff point to define threshold ( a sigmoid, or S-shaped, curve of acuity value) It is similar either use snellen chart or a visual acuity chart with contour interaction control The normal eye will generate a curve with a steep slop, demonstrate a sharp drop-off VA

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62 Snellen chart versus S-chart The inter-letter separations Control for contour interaction The VA levels have large gap at the low end Letters with different degrees of difficulty Frequent re-testing of the VA can result in contamination by memorization

63 Flom s visual acuity test slide

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65 Flom designed a VA test specially for the evaluation of amblyopic eyes Consists of a series of 21 slides Range of VA values from 20/277 to 20/9 Each slide contains a series of eight Landolt C The interletter spacing is equal to the letter diameter, and is surrounded by an equal number of contours The determination of VA use psychometric analysis The number of correct responses is plotted against letter size

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67 A modification of the S-chart Increases contour interaction by reducing interletter spacing to half of the letter size This chart is easier and less confusing to use with children

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69 Telescopic acuity Differential diagnosis between organic and functional amblyopia Any improvement in acuity through a telescope indicates a functional amblyopia That telescopic acuity greater than predicted by the magnification of the telescope indicates a functional amblyopia with good prognosis The pretherapy acuity through the telescope is the predicted acuity following successful therapy

70 Neutral density filter Preadapt the good eye for 5 minutes with the polarized filters Expose an S-chart of 20/42. Slowly rotate the polarizers until the patient can just begin to resolve at least five of the eight LandoltC Similarly preadapt the amblyopic eye for 5 minutes, and then quickly introduce the filter that allow the good eye to resolve Measure VA of the amblyopic eye through the filter, and compare this without the filter VA If VA is reduced considerably more in the amblyopic eye than in the good eye, then organic amblyopia should be suspected

71 Other abnormal aspects of Accommodation Reduced amplitude amblyopic eye Reduce threshold and contrast sensitivity, target fading Accommodative stimulus response Eccentric fixation Increased depth of focus Increased variability of accommodative response Abnormal fixational eye movements, increase drift and jerk nystagmus

72 Other abnormal aspects of amblyopic eye Eccentric fixation Binocularity Motor Cover test at distance and near Sensory Stereopsis, anomalous retinal correspondence

73 Visual acuity, fixation, and direction MAR = E + 1 sense MAR is minimum angular resolution E is eccentricity In 1961, Flom and Weymouth studied the eccentricity of Maxwell s spot in both normal and amblyopic eyes Monocular VA in the amblyopic eye at the point of eccentric fixation was the same as that found in the normal eye at the same eccentricity

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75 Treatment Early detection Correction of any significant refractive error Constant Occlusion Additional active training The effects of occlusion can be enhanced or facilitated by addition of active training

76 Home and office therapy Weekly office session of approximately 45 minutes Daily home therapy lasting from 20 minutes to 2 hours The amblyopic visual system responds best to short regular periods of intense therapy

77 Patching Anywhere from ½ to 6 hours daily Most of the patching done at home Cosmetic is not a major factor

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79 Length of treatment Last from 4 to 6 months Afterward, daily treatment duration will be gradually reduced To prevent regression of vision function Take another 2 months or so

80 Progress evaluation Perform every 8 weeks during the therapy course The goal of amblyopia treatment is to improve vision and sensorimotor function ( eye-hand coordination, focusing, navigation ability, etc.) Monitor improvement in vision function Determine when treatment should be discontinued

81 Motivation The single most important factor contributing toward a successful case Explain to the patient and encourage the patient by setting up situation that will allow the patient to be aware of progress Show the progress of evaluation to patient, have them become actively involved in the therapy process May experience headaches, eyestrain, fatigue, or diplopia during treatment

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83 Training sequences Accommodation Stimulus, monocular to bi-ocular accommodation Eye movements Hart-chart saccades, eye-hand coordination Form recognition Recognize the simple and complex forms with either being hidden, or slightly different from a similar comparison form

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87 Strabismus Strabismus most often develops within the first 6 ~ 7 years of life. Approximately 7% of children aged 6~7 years had strabismus. Strabismus affected approximately 1% of infants ( < 12 months).

88 Risk factors for strabismus Maternal cigarette smoking Neurologic disorders Use of other drugs during pregnancy Heredity Refractive errors Low birth weight( prematurity) Anatomic factors( craniofacial anomalies)

89 Classification of Heterotropia Squint or Strabismus In term of the direction and magnitude of the deviation, heterotropia is classified as either comitant or incomitant. More information are also required to have more detailed classification regarding its frequency, laterality, age of onset, influence of accommodation and cosmesis.

90 Comitant and Incomitant heterotropia The angle of deviation is constant in all direction of gaze called comitant strabismus The incomitant deviation is varies with direction of gaze. The deviation is largest when the eyes are turned in the direction of maximum action of the affected muscle. The term paralysis is used if the action of one or a group of extra-ocular muscles is completely abolished. If the action of muscle is impaired the term paresis is used.

91 Frequency Constant or intermittent Laterality Unilateral or alternating Location Patient may have a phoria at distance and have a tropia at near.

92 Direction Depend on the visual axes deviate from alignment. The tropia is noted by the non-fixating eye. Esotropia, Exotropia, Hypertropia, Hypotropia Deviation of the upper pole of the cornea result in Excyclotropia ( outward) or Incyclotropia ( inward)

93 Age of onset Congenital is the deviation that are present at birth or develop during the first few months of life. Acquired is arisen during childhood or later in life. Presence of nystagmus Should be described in terms of congenital, latent or acquired and whether pendular or jerky.

94 Refractive errors in children The management of refractive errors is of the utmost importance in children with strabismus. Hyperopia was more common in esotropia at the time of diagnosis. A few exopropic children were myopic. The strabismic eye had a greater chance of becoming anisometropic in esotropia.

95 In every child with strabismus, VA should be measured as early as possible to detect amblyopia. The vision in one eye is compared with the fellow eye. VA of 20/200 or less should raise the suspicion of anisometropic amblyopia or other ocular disease.

96 Differential diagnosis Not all monocular vision loss with a strabismic patient is secondary to amblyopia. Only after an extensive examination has been performed otherwise. Careful refraction must be performed and any refractive error corrected before it is assumed. Mild congenital optic nerve pathology as well as small lens opacities can be overlooked. The amblyopic patient has normal color vision, in contrast to the patient with optic neuropathy. Marcus Gunn pupil is rare in strabismic amblyopia

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98 When to treat comitant strabismus There are three good reasons for treating: If they are causing problems If they are likely to deteriorate if left untreated If treatment may be required but less effective when the patient is older.

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101 ( see to learn) ( learn to see)

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103 (3~5 ) ( )

104 At what ages should children be examined All children should be seen at before the end of the first year of life. If there is a family history of strabismus, amblyopia, high refractive error, or early vision loss, the infant should be examined by 6 months of age. If the parents observe any unusual appearance of the child s eyes or visual behavior, they should be evaluated as soon as possible.

105 The child should routinely be seen again between the ages of 2.5 ~ 3.5 years, just before kindergarten, and then yearly through elementary school. This is to ensure early detection of major visual anomalies that might affect the child s general performance.

106 Practice Management Many clinical examination techniques on the young children are quite the same with older children and adults. These may require only few modification of instruction and targets to be effective with young children.

107 Environment Comfort and welcome designed office or reception area reduce the fear and anxiety Select the optimal appointment time Removing the doctor s white coat

108 Observation Hyperactive vs. shy or cautious child Communication with parents Convey clear expression and clearly outline the parent s involvement. The parents will follow the optometrist s lead and will interact with the child at the level of permitted.

109 The Problem Oriented Record The data base A problem solving approach requires the optometrist to think in terms of ensuring the major visual system or function. The data base can be subdivided into the diagnostic areas as following:

110 Examination strategy Case history Refractive status Visual acuity status Binocular status Motor Sensory Accommodative status Ocular health status Developmental perceptual motor status

111 Problem list From the results of data base evaluation the optometrist construct a problem list, which provides an overview of the patient s problems and eliminates the extensive file review prior to future visits.

112 Initial plan This serves as the basis for the plan list, consisting of the therapy and education recommendations. Progress note Used to follow up on the initial management plans and is outlined in SOAP notation

113 S ( subjective): information about course of signs and symptoms, compliance with the management plan, and new concerns. O ( objective): examination findings. A (assessment): the doctor s interpretation P (plan): any modification of the initial plan

114 Primary reason for eye examination Routine check-up Family Hx of visual problems Failed vision screening Referred by GP or teacher Signs noticed by parents Symptoms reported by child Further opinion sought

115 History

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120 Visual Acuity There are several tests available for children. Response to occluding Forced-choice preferential looking ( FPL) is suitable for toddlers from 12 months of age up to 3.5 years old, and for older children with either poor communication skills or delayed development

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122 Children of three years to five years old The Kay picture test Recognition test, pictures of familiar objects are presented to the child

123 The Sheridan-Gardiner test Seven Snellen letters are used in this matching test

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125 phoropter

126 Cycloplegia Cycloplegia cycloplegia

127 Near fixation retinoscopy The Mohindra technique Mohindra (1975) 50 trial lens or lens racks -1.25D

128 Mohindra technique subjective refraction cycloplegic refraction 18 ~ 48

129 Dynamic retinoscopy Dynamic retinoscopy low neutral point high neutral point NRA

130 static retinoscopy, other objective refractive and subjective refractive findings 0.50D

131 Subjective refraction

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