A young patient with oculocutaneous albinism and sensory nystagmus
By J.P.Lowery, O.D., M.Ed.
Pacific University College of Optometry
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I. INTRODUCTION
Visual impairment in children has profound developmental implications. The optometric physician who possesses an understanding of conditions which cause visual impairment can play a key role in enhancing visual and general development for these children. Some of these conditions such as retinopathy of prematurity, cataracts and glaucoma require initial medical management beyond the scope of optometric care, but all visually impaired children benefit from long term optometric management. In addition to traditional low vision services, the optometric physician can provide valuable insight regarding visual function, assessing the educational and environmental needs of the child and recommending strategies to maximize developmental potential.
Visual impairment is considered a low incidence
disability in children accounting for about 0.1% of the school-aged
population.(1) The majority of visually impaired children are
multiply-handicapped with coincident disorders such as cerebral
palsy, seizure disorders, hearing deficits and developmental delays.(2,3)
The optometrist who works with visually impaired children should
have a keen understanding of these conditions that often accompany
and contribute to visual disability. The multiply-handicapped/visually
impaired population continues to grow as advances in neonatal
medicine allow us to save more and more babies born in critical
condition.
Definitions
Legal Blindness in its most simple form, is defined as best
corrected distance acuity of 20/200 or worse in the best eye.
Better than 20/200 central acuities are allowed within the definition
if accompanied by significant visual field loss. The PDR For Ophthalmology
contains an excellent reference section outlining the exact criteria
for legal blindness based on levels of acuity and field loss.
Visually Impaired is defined by a certain level of acuity and/or field loss which varies slightly from state to state. It is important to know your regional eligibility requirements because visually impaired status makes a child eligible for special education services which may be critical to the child's academic success. The criteria used by most states is best corrected distance acuity of 20/70 or worse in the better eye or a visual field restricted to 20 degrees or less in the better eye.
These definitions are not very useful in describing the visual function of a child. The optometric physician must look at many other factors beyond distance acuity in order to determine overall visual function. The clinician must sometimes make a judgment call reporting an acuity based on less than adequate data as many of these children are difficult to examine. It is better to error on the conservative side, which allows a child to be eligible for help that may improve developmental potential significantly.
II. COMMON CONDITIONS OF VISUAL IMPAIRMENT
1. Congenital Nystagmus
The first concern when a child presents with nystagmus is to rule out active neuropathology associated with vestibular, upper brainstem or cerebellar lesions. In this case the nystagmus is considered acquired rather than being secondary to a congenital visual-sensory or visual-motor disorder.
Differential diagnosis of congenital vs acquired nystagmus:
Age of onset: Congenital nystagmus usually presents prior to one year of age but can present as late as six years of age if secondary to the onset of anterior visual pathway pathology. Any initial presentation of nystagmus after six years of age should be considered acquired secondary to active neuropathology and immediate referral to the neurologist is warranted.
Acquired nystagmus often changes direction in different positions of gaze becoming upbeating in superior gaze and downbeating in inferior gaze while congenital nystagmus remains horizontal in all gaze positions.
Congenital nystagmus is almost always binocular and conjugate (symmetrical between the eyes), while acquired is often unilateral and disconjugate.
Acquired nystagmus presents with recent onset of signs/symptoms of active neuropathology. The patient will likely report onset of oscillopsia (awareness of oscillating field movement)
Congenital Nystagmus may be due to a developmental abnormality of the oculomotor system (Efferent) or secondary to bilateral central vision impairment (Afferent).
Afferent or Sensory Nystagmus:
Afferent nystagmus is associated with sensory deprivation such as in macular scarring, optic nerve hypoplasia, macular hypoplasia, albinism, retinal degenerations, and achromatopsia. Nystagmus will manifest at 4 to 8 months when central vision is impaired from birth and may develop secondary to vision loss up to six years of age.(4)
Afferent nystagmus often presents as a pendular wave form and is often dampened on convergence. Sometimes an esotropia is present as an adaptive measure to increase acuity (Nystagmus Blockage Syndrome).
Efferent or Motor Nystagmus:
The usual etiology of congenital efferent nystagmus is a hereditary or developmental motor abnormality. The wave form is usually jerk, with a fast phase in one direction and a slow phase in the other.
Usually a null point is present somewhere between far left and right horizontal gaze or, sometimes, upgaze. At this gaze position, the nystagmus is diminished and acuity is best. The patient will often acquire a head posture to place their eyes at the null point during demanding acuity tasks.
Clinical note regarding wave form: Although pendular nystagmus usually presents with ocular pathology and jerk usually goes with a motor defect, it is possible to have mixed types in the same patient regardless of etiology. Often pendular will change to jerk form in lateral gaze positions. Congenital nystagmus is also characterized by variability in amplitude and frequency. Unfortunately, the nystagmus often becomes more intense when the child concentrates or is under stress.
Latent Nystagmus:
Manifests only when one eye is covered
Monocular VA's much poorer than binocular
Management of congenital nystagmus:
Typically, children with nystagmus in the absence of other, more severe visual or cognitive impairments can achieve their academic potential. Near acuity is usually better than distance.
Suggestions for enhancement of visual function include:
Correction of refractive error, especially if significant
Low power, larger field magnifiers for near
Monoculars for distance
Apply prism to place eyes in null point positions; base out for convergent null points, yoked for lateral gaze null points.
Extraocular muscle surgery is sometimes employed in cases where a significant null point is found in an extreme position of gaze.
Contact lenses (RGP's) can have a dampening effect on nystagmus due to tactile feedback. However, this effect may diminish with decreased corneal or lid sensitivity over time.
A young patient with oculocutaneous albinism and sensory nystagmus
2. Albinism
Albinism is one of the most common forms of inherited visual impairment. A wide spectrum of genetic variants exist, many of which have associated metabolic or central nervous system anomalies, most commonly hearing impairment.
Anatomically, albinos exhibit excess decussation of optic nerve fibers at the chiasm with temporal retinal fibers that normally remain ipsilateral crossing to the contralateral geniculate body. This anomalous wiring limits binocularity as well as accuracy of fixation and pursuits.(5)
It is characterized by varying degrees of amelanosis due to a deficiency of the enzyme tyrosinase.
Ocular complications - Level of visual
impairment is dependent on the degree of severity of these five
factors:
Amelanosis of the iris and retina
Nystagmus
Foveal hypoplasia
Strabismus and impaired binocular vision
Astigmatism
Classification of Albinism:
Albinism occurs in two primary types, oculocutaneous and ocular. There are many genetic variants of oculocutaneous albinism in which both skin and eyes are affected. Most of of these variants are inherited in an autosomal recessive pattern.(5) However, the most useful division of oculocutaneous albinism for the eye care practitioner is based on the expression of the gene for the enzyme tyrosine because the degree of ocular involvement is tied to the deficiency of tyrosine and corresponding amelanosis.
Oculocutaneous Albinism:
1. Tyrosinase-Negative
The most severe form in which there is complete absence of pigment.
Foveal light reflex is absent (complete foveal hypoplasia).
Nystagmus is moderate to severe.
Acuity is usually 20/200 or less.
2. Tyrosinase-Positive
Characterized by varying degrees of amelanosis.
Foveal hypoplasia and nystagmus is not as severe as T-Negative.
Acuity is usually better than 20/200.
Anterior segment presentation of a young black with oculocutaneous albinism
Fundus of the same patient.
Ocular Albinism:
X-linked recessive inheritance
Affected males have normal skin and hair pigment but show varying degrees of ocular depigmentation.
Visual acuity lies in the 20/40 to 20/100 range. (Correlates with the amount of pigment and nystagmus.)
Mother's eyes are affected. (Subclinical presentation.)
Some presentations of ocular albinism, especially in darkly pigmented individuals, can be easily missed because there is no iris transillumination and the fundus appears nearly normal. Slightly reduced acuity and mild nystagmus may be the only observable signs.
Albinism Management Strategies:
Fully correct astigmatic refractive errors with appropriate reading adds.
Illumination/glare control strategies: photochromic lenses with an underlying #1 amber tint and UV block, 2 5% transmission amber sunglasses, tinted overlays, yellow reading lights.
Standard low vision devices may be applied as needed.
Note: Albinos usually show normal academic achievement and lead normal lives with low magnification aids for near work. This is because near acuity is much better than far, primarily due to nystagmus dampening with convergence.
3. Congenital Cataracts:
Congenital cataracts are associated with metabolic disorders, genetic disorders, birth trauma and maternal infection such as Rubella.
Surgery is only performed in cases where functional acuity is significantly impaired. The small size of the eye and strong adherence of the vitreous to the posterior lens capsule and retina in young children makes surgery difficult. Secondary vitreous trauma with opacification of the remaining capsule is common. However, visually debilitating cataracts are extremely amblyogenic and must be removed within a few months of birth.
Aphakia is the necessary surgical result in neonates, however IOL's are being placed in children as young as 3 years now.
Exact aphakic correction with a high bifocal add (3 - 5 diopters depending on the age of the child and habitual working distance) is important. Additional low vision aids may be necessary. Contact lens correction with reading glasses is the best option when possible. Successful fitting and long term wear can be achieved in the majority of cases.(6)
Glare needs to be controlled in all work environments. The same management strategies as albinism may be utilized.
Congenital Anterior Polar
Cataract
4. Congenital Glaucoma
This is rare but highly destructive to vision if not detected and treated early. Signs of infantile glaucoma include: Tearing, photophobia, cloudy cornea, enlarged corneas, high IOP, disk cupping and/or asymmetry.
Congenital glaucoma may be present at birth or develop early in the infantile period.
Corneal enlargement occurs if high IOP is present from birth to two years.
Syndromes of anterior segment dysgenesis (Reiger's syndrome, Peter's anomaly, Aniridia) may produce a secondary glaucoma during childhood.
Even with aggressive long term medical/surgical management by a glaucoma specialist, visual outcome is often very poor with corneal scarring from endothelial compromise and severe edema as well as nerve fiber loss resulting in restricted fields.
Optical management consists of standard low vision devices and glare control.
Careful monitoring of IOP is usually necessary throughout life.
5. Retinopathy of Prematurity
ROP is not technically a congenital condition. However, there may be congenital factors that predispose the infant to premature birth and its complications which include ROP.
The exact mechanism of ROP is complex and not completely understood. We know that it is associated with low birth weight and supplemental oxygen therapy, but other factors including light exposure in neonatal ICU's may play a role in specific cases. In the premature infant eye, the retinal vasculature is poorly developed, especially in the temporal periphery. In ROP, a ridge of tissue develops at the border of the vascularized and non-vascularized retinal tissue. From this border, small vessels proliferate and undermine the structural integrity of the retina and overlying vitreous. Cicatricial changes in the temporal periphery also lead to traction and temporal dragging of the macula and retinal vessels from the optic nerve. The active phase can ultimately lead to retinal detachment and scarring.
ROP usually develops at 34 to 40 weeks after conception, regardless of age at birth. When retinal detachment does occur, it usually progresses from the retinal periphery and some central vision may be saved. Over 90% of cases do not progress to the retinal detachment stage and the proliferating vessels regress resulting in normal to near normal vision. However, patients with a history of regressed ROP are at significant risk for retinal detachment as the eye continues to grow. These patients need careful peripheral retinal examinations on a yearly basis through childhood and early adulthood.
There are five stages recognized in the International Classification of ROP:
1. Demarcation line between vascular and avascular retina
2. Ridge developed at the demarcation line with retinal vascular traction
3. Ridge with extraretinal fibrovascular proliferation
4. Subtotal retinal detachment
5. Total retinal detachment
Advanced ROP with vessel tortuosity and proliferation of abnormal vessels along border between vascular and avascular retina.
Mild dragging of the macula.
Advanced ROP resulting in severe traction and detachment/scarring in the temporal periphery (ROP photos courtesy of Casey Eye Institute, Oregon Health Sciences University)
Treatments of choice are laser photocoagulation or cryotherapy to burn or freeze the peripheral retina in ROP that has reached stage 3. Vitrectomy with surgical reattachment is sometimes attempted in advanced cases.
Functional vision characteristics:
Residual vision ranges from total blindness to near normal.
Visual field loss depends on the extent of retinal detachment and scarring. Often there is only a small area of central retina that is useful.
High myopia is prevalent (6 - 24 Diopters). The child will often assume an eccentric fixation position that uses the best part of the remaining retina.
ROP Management Strategies:
Best correction of refractive error is attempted. Often, the child will reject the glasses due to the minification effects of high minus lenses, or because there is no subjective improvement in vision. In other cases, retinoscopy may show high myopia but acuities are far better than expected from the apparent refractive error. It is important to perform retinoscopy on the axis of habitual eccentric viewing as topography of the retina may be quite variable. The best functional application of correction is usually achieved with 2/3 to 3/4 of the myopia found with retinoscopy.
Early intervention with visual stimulation activities to encourage the ROP child to use his or her residual vision
Orientation and mobility (O&M) training is critical with peripheral field loss.
Figure-ground exercises as a part of O&M training.
Monoculars for distance tasks
The ROP child may not require any near magnification due to high myopia which allows the him or her to read adequately with a very close working distance. The child should be allowed to take off the glasses for near work.
Often there are underlying developmental cognitive/behavioral issues that need to be addressed.(7) It is important to remember that most of these children are born extremely premature. Respiratory distress leading to anoxic brain damage is very common.
6. Hereditary Retinal Conditions and Photoreceptor Abnormalities
This is a very large category of visual disabilities and all cases vary with the type of retinal disease and residual vision. A detailed discussion of the genetics and diagnostic criteria for all the hereditary retinal dystrophies is beyond the scope of this paper. There are many excellent reference sources that provide thorough coverage of these conditions.(8,9) Here, we will focus on diagnosis, visual function and the low vision management of the most commonly encountered of these conditions.
Hereditary retinal conditions can be functionally divided into conditions that primarily affect the rods versus those that primarily affect cone function. Table 1 summarizes this functional dichotomy with a short list of the most common diseases that fall into each category.
Table 1 - Hereditary Retinal Disease: Signs, Symptoms, and Diseases Based Photoreceptors Primarily Affected
|
RODS |
CONES |
|
SIGNS AND SYMPTOMS: Reduced Night Vision |
SIGNS AND SYMPTOMS: Photosensitivity |
|
DISEASES: Retinitis Pigmentosa |
DISEASES: Stargardt's Macular Dystrophy |
Retinitis Pigmentosa is a group of related disorders affecting rod metabolism leading to progressive atrophy of the rods in the retinal periphery. Cone apoptosis occurs secondarily. Onset is insidious and progression is usually slow. Some RP patients retain usable vision throughout life, however, if vision is significantly affected in childhood, it is very likely to progress to complete blindness during productive years. In RP, because the rods are affected initially, reduced night vision is the first symptom. As the disease progresses, there is a slow loss of peripheral field until finally the macula and optic nerve are affected with complete blindness.
There are many forms of RP that do not follow recognizable inheritance patterns. However, the majority follow an autosomal recessive pattern (60%), an autosomal dominant pattern (15%), and X-Linked pattern (10%). The AR and X-Linked forms are the most severe with development of night blindness in early childhood with progressive field loss and central vision involvement by teens or twenties. The AD form tends to be less severe with later onset of signs and symptoms and central vision remaining until the 4th decade or longer.
The initial fundus changes that are seen in most forms of RP are the characteristic bone-spicule pigment accumulation and arterial attenuation. Vessel attenuation may be the first observable sign and should alert the clinician to the possibility of RP when a young patient presents with poor night vision. Abnormal scotopic ERG will confirm RP and may be helpful in cases where fundus signs are unclear.
Typical mid-peripheral pigmentary changes associated with retinitis pigmentosa.
Posterior pole presentation of RP showing arterial attenuation and optic atrophy.
Many of the RP syndromes are associated with systemic anomalies such as hearing loss (Usher Syndrome), mental retardation, and ataxia. Posterior subcapsular cataracts develop at some point in about 50% of cases. Currently, RP remains untreatable. Various experimental metabolic supplements have been tried including Vitamin A and Lutein therapy. However, clinical trials have demonstrated only transient slowing in the progression of acuity or field loss.(10)
Leber's Congenital Amaurosis is a disease with very similar characteristics to RP except the child is blind at birth or within the first year of life. A searching nystagmus will be present but retinal signs may be minimal for the first few years. ERG is usually necessary for diagnosis.
Low Vision Management:
Poor night vision makes good illumination critical. A wide-beamed pocket flashlight is a good recommendation.
Field loss needs to be documented carefully with threshold perimetry as patients often perform as if they have better fields than they actually do. Acuity can still be near normal with only 5-10 degrees of total field.
In advanced cases with tunnel vision and reduced central acuity, magnification devices may be necessary for fine acuity tasks. However, magnification reaches a point of limited value when patients have extremely constricted fields. Monoculars and near magnifiers are difficult to use at this point. CCTV is often the best means of reading in advanced cases.
Field expansion devices can be attempted but are often rejected due to extreme minification. An inexpensive means of trialing field expansion is using a door peep purchased at the local hardware store.
Although prism or mirrors can be positioned to place more of the field within the patients usable vision area,(11) the success of these devices requires an adaptable patient.
Children need to be prepared for blindness so braille and mobility training should be started early in the course of field loss. Parents and children often have difficulty being realistic about vocational limitations so they should be informed that there are many Retinitis Pigmentosa help groups that can be accessed through local commissions for the blind or the internet.
Hereditary retinal conditions that primarily affect central vision include Stargardts, and Vitelliform (Best's) Macular Dystrophies and Progressive Cone Dystrophy. All of these conditions present in the first or second decade of life with declining central acuity as the first sign and central scotomas developing as observable macular changes appear. Normal peripheral vision is maintained and resultant acuity is usually in the 20/100 to 20/400 range. The individual will typically take on an eccentric fixation pattern to utilize healthy paracentral retina.
Stargardt's, the most common of the hereditary macular dystrophies, can be particularly difficult to diagnose in the early stages because significant acuity loss may precede any observable macular changes. Conversely, in Vitelliform Dystrophy, significant macular changes usually precede acuity loss. In contrast to Stargardt's and Vitelliform Dystrophies, Cone Dystrophy presents with poor color vision and reduced photopic ERG because cone function is affected throughout the retina.
Progressive stage of Vitelliform dystrophy.
End-stage Vitelliform dystrophy.
Management:
These children do well with standard low vision devices, magnifiers
and monoculars. Mobility is usually not affected except for the
need to use monoculars for street signs, bus numbers, etc. People
with macular dystrophies can be productive adults with minimal
disability when fitted with the appropriate low vision devices.
Congenital Conditions of Photoreceptor
Abnormality are non-progressive
genetic diseases that a child is born with. The two most common
types are: congenital stationary night blindness (CSNB) and achromatopsia.
In CSNB, the rods are primarily affected resulting in poor night
vision with mildly reduced visual acuity. Visual fields are restricted
in low light conditions. Nystagmus is sometimes present and will
reduce acuity further.
In Achromatopsia (also called Rod Monochromatism) there is abnormal or complete absence of cone function. Color vision is limited or absent. Acuity ranges from 20/40 - 20/100 in the abnormal form and 20/200 in the complete form. Nystagmus is present to varying degrees depending upon the form of the disease.
Management:
Vision is reduced under bright conditions and the child is photophobic.
An ideal range of illumination for these patients is dark enough
to keep the rods turned on, but still light enough to see. Contrast
is critical to visual performance. Amber tinted photochromic lenses
in sunglass frames with side shields and low power magnifiers/monoculars
are appropriate optical aids.
7. Optic Nerve Hypoplasia:
In this condition, the optic nerve fails to develop completely resulting in less than the normal number of axons. The presentation is usually bilateral but may be asymmetric.
Appearance is of a small gray or pale nerve head surrounded by a mottled peripapillary halo. The halo represents the underlying lamina not covered by nerve head axons. Many morphological presentations are possible and diagnosis may be difficult by observation alone.
Moderate to severe presentation of optic nerve hypoplasia
Diagnosis is aided by measurement of the ratio of the disc to macula distance compared to the disc diameter (DM/DD). Normally, 2.1 to 3.2 disc diameters fit in the space between the temporal disc margin and the fovea. Any value higher than this range indicates possible optic nerve hypoplasia, especially if this value is 4 or greater. Another helpful diagnostic observation is the relative width of the vessels compared to the disc diameter. Normal vessel diameter to disc diameter ratios fall in the 1/5 to 1/6 range. Stereophotos can be helpful for careful analysis of these anatomical factors and the depth of the neuroretinal rim tissue.
It is often associated with developmental central nervous system or endocrine disorders. Cognitive deficiencies and multiple handicaps are common.
Acuity varies from light perception to normal and pupillary responses are reduced depending upon the severity of hypoplasia.
Pupil responses are reduced in more severe forms.
Secondary nystagmus is usually present.
Low vision intervention depends upon the level of developmental impairment of the child. Correct high refractive errors even if a subjective improvement cannot be measured.
8. Congenital Optic Atrophy
There are several types of primary hereditary optic atrophy syndromes, most of which have no associated central nervous system anomalies.
Early acquired cases are associated with broad neurological damage. Common etiologies include trauma, intrauterine teratogens (Fetal Alchohol Syndrome), perinatal ischemic event, and hydrocephalus (papilledema).
Extent of visual impairment can be estimated by the extent and depth of nerve head pallor and attenuation of pupillary responses. Central scotomas and nerve fiber defects are common.
Color vision is almost always impaired and secondary nystagmus may be present.
Presentation of a 12 year old female with autosomal dominant congenital optic atrophy (best corrected acuity was 20/150 in each eye).
Low vision management in uncomplicated hereditary syndromes consists of standard optical devices, mobility training for field loss, and provision of adequate lighting.
9. Coloboma
Colobomas result from failure of the fetal fissure to close in early embryological development.The presentation ranges from an insignificant chorioretinal defect to a complete fissure involving the optic nerve and macula running inferiorly across the retina/choroid to involve the ciliary body and iris.
Other associated embryological abnormalities may be present.
Acuity may be reduced depending on the extent of optic nerve and/or macular involvement.
Central, superior field loss corresponds to the extent of the coloboma.
Searching nystagmus may be present.
These children respond well to magnification and usually do not have significant difficulty with mobility.
Optic nerve head coloboma.
Large inferior coloboma.
Visually devastating coloboma involving the nerve head and macula.
10. Cortical Vision Impairment:
The patient's history is positive for cerebral insult; traumatic, vascular, metabolic, pathological, developmental or degenerative.
Recent data indicates that cortical impairment is now the most prevalent form of congenital visual impairment accounting for primary diagnosis in 35-50% of cases.(12,14)
Nearly all children with cortical vision impairment are mentally and multiply-handicapped to some degree.
Diagnosis is based on the following:
The anterior visual pathway (eye and optic nerve) is healthy yet the child lacks normal visual behavior.
OR
An anterior pathway pathology (frequently optic atrophy) may be present but it is not significant enough to account for the lack of visual response.
VER (visually evoked response) and MRI (magnetic resonance imaging) evaluations can be of some value but behavioral observations are the most useful pieces of the diagnostic picture.(12,13)
CVI children exhibit certain visual behaviors
that demonstrate a lack of
basic visual attention and visual perceptual skills. Observation
of these behaviors completes the clinical picture of cortical
vision impairment.
Behavioral characteristics:
1. CVI children demonstrate short or highly variable attention span and inconsistent visual behavior.
2. They have poor or no central fixation, often using the peripheral visual system. The child may appear to be completely blind due to lack of fixation, yet still be able to reach out to grasp an object or walk through a room avoiding obstacles. This unique visual behavior is referred to as blind sight. What we know of functional neurology leads us to believe that blind sight occurs via a secondary visual pathway that branches off the optic tract to enter the superior colliculus. This area of the midbrain appears to be involved in monitoring peripheral vision and orienting attention toward novel stimuli.(15)
3. They show greater responsiveness to close objects in an uncrowded visual environment. Figure-ground ability is poorly developed due to lack of cortical processing of detail in the visual environment.
4. Often CVI children are more responsive to bright colors (esp. red) or high contrast objects. Color vision is processed more globally in the visual cortex than specific elements of form, and thus may be spared even with significant neuron loss.(12)
5. CVI is not typically accompanied by nystagmus, although random eye movements may appear nystagmoid at times.
Developmental Management
As in amblyopia, CVI children require early intervention when the cortical neurons are primed to produce new dendrites and synapses. With basic visual stimulation activities, many of these children can develop oculomotor and visual perceptual skills. It is difficult even for developmental neurologists to provide prognosis in any given case. CVI children often appear to be completely blind at birth but slowly develop visual responses over the course of the first few years. I have even seen children show significant improvement in middle childhood (6 - 10 years) when a consistent program of visual stimulation was initiated. Teacher's of the visually impaired who routinely work with these children can help integrate appropriate visual activities into the daily routine. The optometrist can provide valuable direction for home therapy with developmentally appropriate suggestions. Therapy should be aimed at increasing visual attention span through fixation and pursuit exercises, and then moving to visual discrimination exercises using tactile and auditory reinforcement. Higher functioning CVI children benefit from figure-ground, visual memory, and visual-spatial activities.(16,17)
CONCLUSION
There are certainly many other conditions of childhood visual impairment that deserve coverage, degenerative myopia for example. However, the sample presented here was chosen not only because of the relative prevalence of the conditions but also to provide adequate representation of the functional vision problems that are present in the population as a whole. In part II of this series, assessment and management strategies will be presented to provide the optometric physician with clinical tools for working with visually impaired children. The developmental impact of childhood visual impairment and the role of the optometric physician in addressing these issues as part of the multidisciplinary team will also be discussed.
REFERENCES
1. Heward, William L., Orlansky, Michael D. Exceptional Children (1992) New York: Macmillan
2. Robinson GC, Jan JE, Kinnis C. Congenital Ocular Blindness in Children. 1945- 1984. Am J Dis Child. 1987: 141: 1321-1324
3. Takeshita, B. Developmental Low Vision for Partially Sighted Preschoolers. J Opt Vis Dev 1996; 27: 224-31
4. Rosenbloom, Alfred A., Morgan, Meredith W. Principles and Practice of Pediatric Optometry (1990) p. 343 Philadelphia: JB Lippincott
5. Lyle WM, Sangster JOS, Williams TD. Albinism: an update and review of the literature. J Am Optom Assoc 1997; 68: 623-45
6. Moore, Bruce D. Success rate in the use of contact lenses for the treatment of pediatric cataracts. Optom and Vis Science 1992; 69:
7. Alward, GP. Pfeiffer, ST. Wright, A. Verlhurst, SJ. Outcome studies of low birth weight infants published in the last decade: A metaanalysis. J of Pediatrics 1989; 115: 515-20
8. Alexander, Larry J. Primary Care of the Posterior Segment (1989) East Norwalk: Appleton and Lange
9. Traboulsi, Elias I. Genetic Diseases of the Eye (1998) New York, New York: Oxford Universtiy Press
10. Dagnelie, G. Zorge, I. McDonald, T. Lutein improves visual function in some patients with retinal degeneration: a pilot study via the internet
11. Cohen, Jay M. An overview of enhancement techniques for peripheral field loss. J Am Opt Assoc 1992; 63:60-70
12. Jan, JE. Wong, P. The child with cortical visual impairment. Seminars in Ophthalmology 1991; Vol. 6, No. 4, pp 914-20
13. Jan, JE. Groenveld, M. Visual behaviors and adaptations associated with cortical and ocular impairment in children. J Vis Impair and Blind, April 1993; pp101-105
14. Williamson, WD. Desmond, MM. Andrew, LP. Hicks, RN. Visually impaired infants in the 1980's. A survey of etiological factors and additional handicapping conditions in a school population. Clin Pediatr (Phila) 1987 May; 26(5): 241-44
15. Jan, JE. Wong, P. Groenveld, M. Flodmark, O. Hoyt, CS. Travel Vision: "collicular visual system"? Ped Neurology. 1986, Vol.2, No.6, pp359-62
16. Bell, J. An approach to the stimulation of vision in the profoundly handicapped, visually handicapped child. British J Vis Imp 1986 (IV:2), 46-48
17. Bortner, S. James, M. Simon S. Goldblatt, S. Sensory Stimulation Kit; A Teacher's Guidebook. American Printing House for the Blind Inc. Louisville, Kentucky, U.S.A. 1982
Contact the Author:
J. P. Lowery, OD, MEd
Pacific University College of Optometry
2043 College Way
Forest Grove OR 97116
loweryj@pacificu.edu
Note:
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