FP1149 : Cerebral Visual Impairment [CVI] is a Differential Diagnosis of Recalcitrant Amblyopia.

Dr. Zia Chaudhuri, C07237, Dr. Gunjan Rana

Abstract

A prospective, cross-sectional evaluation of 92 subjects [M:F::51:41] with acquired unilateral and bilateral CVI comprising traumatic brain injury [TBI], dementia, cerebral hypoxia, infections and space-occupying lesions [SOL] across ages between 6-80 years revealed equivocal distribution of decrease in contrast sensitivity values, speed of reading [MN Read Charts], near vision, stereopsis and visually evoked potential [VEP] across different ages and etiologies of CVI. Colour vision and visual field defects were also equivocally distributed. In the absence of any other structural changes in the eye, this cohort, especially bilateral CVI in children simulated amblyopia and is thus an important differential diagnosis of the same. Thus CVI must be considered with high suspicion in subjects with recalcitrant amblyopia non-responsive to treatment. Neuroimaging in these cases may be useful. The findings on neuroimaging in this study were varied but the visual impairment was similar.

Key-words: cortical visual impairment (CVI), dementia, traumatic brain injury (TBI)

Key Messages: Microangiopathy due to previously undiagnosed pre-diabetic status may contribute to self-limiting acute acquired comitant esotropia(AACE)in patients with no other structural or metabolic anomaly other than the mildly raised HbA1C levels. Neuroimaging and metabolic work up is thus of help.

 

Introduction

The visual system is a major perceptual system. Visual impairment can be divided into 2 categories, namely ocular visual impairment and cerebral visual impairment (CVI). Cerebral visual impairment (CVI) is defined as a temporary or permanent visual impairment caused by the disturbance of the visual pathways in the brain. The burden of CVI has always been high in the first-world countries but appears to be increasing globally with a higher extent of child survival rates in the third world countries.¹ It is probably not a true increase but the fact that this group is increasingly being identified in low income and low middle-income countries. CVI is best identified and diagnosed by a normal eye exam or an eye exam that reveals an eye condition that cannot in entirety explain the profound lack of functional vision, a medical history that includes neurological problems and the presence of unique visual and behavioural problems²The unique visual and behavioural characteristics of CVI include distinct colour preferences, attraction to movement, visual latency, visual field preferences, difficulties with visual and environmental complexity, light gazing or non-purposeful gaze, difficulties with distance viewing, absent or atypical visual reflex responses, difficulties with visual novelty and absence of visual guided reach.²Here, it is important to differentiate CVI from autism spectrum disorder (ASD). ASD results in qualitative impairments in social interaction and communication, with restricted, repetitive, stereotyped patterns of behaviour, interests and activities.³ These behaviour manifest along a wide spectrum and commence before 36 months of age.³CVI, on the other hand can be congenital or can be acquired later in life. In autism, comorbidity with mental retardation, epilepsy, disruptive behaviours and learning difficulty is present and associated aggression, hyperactivity, self-mutilation, temper tantrums can be a part of clinical presentation.⁴Recent neuroimaging research studies indicate that autism may be caused by atypical functioning in the central nervous system, particularly in the limbic system: amygdala and hippocampus.⁴ Additional damage may appear as a consequence of an episode of status epilepticus initiated by previous epileptogenic brain lesion.⁴

 

Materials and Methods

This cross-sectional prospective observational study on subjects with CVI was conducted in the Department of of Ophthalmology of Lady Hardinge Medical College and Associated Hospitals from November 2015 to April 2017. In this study, 92 cases of cerebral visual impairment (CVI) were enrolled as per inclusion and exclusion criteria. Out of these, 31 cases were in the age group 6 to 18 years (Group 1), 30 cases were in the age group of >18 to 60 years (Group 2) and 31 cases were in the age group of >60 to 80 years (Group 3). The analysis was repeated in most intances by redistributing the recruited subjects with respect to the etiology of the CVI. These main groups were those with dementia, cerebral ischemic causes of decrease in vision, infective etiology of the CVI, trauma and ICSOL. The functional vision evaluation comprised assessment of contrast sensitivity, speed of reading [MN Read Charts], near vision, stereopsis and visually evoked potential [VEP] across different ages and etiologies of CVI.

Results

The important observations derived from this study were that all functional visual parameters like CS, SOR, CVD and binocularity were equivocally distributed in all cases of CVI irrespective of the age of the subjects as well as the etiology of the CVI. Quantitative valuation of CS and SOR, though equivocally distributed in each group by age or etiology, were lower than standardized population based normative values for these tests. Similarly, the distribution of CVD was equivocal and varied from 10 to 19% in different sub-groups. HRR test was better for assessing blue yellow CVD. While both Ishihara and HRR were equivocal while assessing red-green CVD, neither test could elucidate whether the CVD was congenital or acquired. This becomes a major limitation in assessing the usefulness of these tests. It could be extrapolated that those with unilateral CVD as well as female subjects with CVD could be having acquired CVI. However, the very presence of CVD in cases of acquired CVI, reiterates the recommendation that easily available tests like the Ishihara be performed in these cases routinely. Cases with an infective etiology for CVI were distinctive in not demonstrating CVD. Interestingly, none of these subjects also had disc pallor. The numbers were probably too less to ascertain the significance of this distribution. As regards binocularity, there was an under-performance of binocular tests on the TNO test with respect to other tests that were performed by these subjects, mainly, the Titmus Fly test, the Lang test and the Frisby Davis test. This could be attributed to the fact that out of these, it is only the TNO test that offers no monocular cues for stereopsis testing and is thus indicative of true binocularity. Other structural changes in the eye like the position of the eye (fundus torsion angle), presence of disc pallor and other ophthalmic associations not resulting in significant visual loss that could commensurate as being causal for the visual impairment, were equivocally distributed in all groups, distributed by age or etiology.Near vision anomalies were equivocally distributed in all groups and did not fundamentally appear to be a function of the CVI. VEP latency and amplitudes was usually normal in cases of CVI irrespective of the etiology as well as age groups of the subjects. Visual field changes were non-specific irrespective of the etiology as well as age groups of the subjects

Discussion

Both unilateral and bilateral visual impairment due to CVI may simulate amblyopia. This condition must be considered with high suspicion in cases of recalcitrant amblyopia not responding to standardized protocols of occlusion therapy. Neuro-imaging may be useful in delineating the cause of the CVI.  This may thus be recommended in those cases where there is no improvement in BCVA after refractive correction as well as amblyopia therapy as per SOP. The findings on neuro-imaging may be extremely varied but the visual impairment is usually similar and not directly dependent on these findings seen.

References

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3. Wing L, Gould J. Severe impairments of social interaction and associated abnormalities in children: epidemiology and classification. J Autism Dev Disord 1979;9(1):11-29.
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