Why Phineas Gage is known as the "man who began neuroscience?"

Phineas Gage was a railroad worker born in July 1823 in New Hampshire, U.S. (died in May 1860 in California) who survived a traumatic brain injury caused by an iron rod that penetrated his skull, obliterating the left frontal lobe and causing changes in his personality. His case lead to the recognition of different parts of the brain being used for different purposes. In researchers using neuroimaging techniques, reconstructed Phineas Gage's skull, to determine the injury to both the left and right prefrontal cortices resulting in problems with emotional processing and rational decision-making.

Visual Pathways and Basic Science of Vision:

Sensation occurs in the occipital lobe; integrated functions involve white matter pathways to temporal, parietal, and frontal lobes. Two principal pathways: dorsal stream (spatial orientation) and ventral stream (form perception and visual memory).

Ventral stream (what pathway) to the temporal lobe for object identification.

Dorsal stream (where pathway) terminating in the parietal lobe for spatial locations.

What is Cortical / Cerebral Visual Impairment (CVI)?

Cortical / Cerebral Visual Impairment is vision loss arising from retrogeniculate pathway damage, surpassing expectations for ocular pathology, excluding anterior afferent visual pathways or ocular structures including insults at the cortex and subcortex levels, including geniculostriate and white matter lesions leading to periventricular leukomalacia. Delayed Visual Maturation is considered part of the CVI spectrum, linked to temporary dysfunction of higher cortical centres.

CVI is a leading cause of visual impairment globally, especially prevalent in developed countries, with increasing occurrences worldwide. Children with multiple disabilities may have additional visual impairments due to uncorrected refractive errors, cataracts, nystagmus, retinopathy of prematurity, optic nerve atrophy, and delayed visual maturation. Steady rise in CVI prevalence, from 36 per 100,000 in the late 1980s to 161 per 100,000 in 2003.

Evolution of Terminology

In 1980, adults with bilateral occipital cortex insult was termed cortical blindness. Since 1980, evolved to cortical visual impairment; in Europe, now termed cerebral visual impairment. "Cortical / Cerebral Visual Impairment" is favoured over "Cortical Blindness" due to the plasticity of the central nervous system and the presence of extra-geniculostriate pathways, preventing total sight loss. Some prefer "Cerebral Visual Impairment" due to subcortical optic radiation involvement, particularly in premature infants at risk for periventricular leukomalacia. Regardless of terminology, cortical or subcortical neurological injuries in young children ultimately affect the cerebral cortex. Perinatal or postnatal hypoxic ischemic encephalopathy, particularly among term or preterm infants, is the most common cause of CVI. CVI is the most common cause of visual impairment in patients with cerebral palsy, with around half of children with CVI diagnosed with cerebral palsy. Boys may be more affected by CVI than girls, presenting an interesting aspect of its impact.

What is Delayed Visual Maturation (DVM) and pediatric cortical visual impairment (PCCWI)?

Congenital or acquired brain based visual impairment with onset in childhood unexplained by an ocular disorder and associated with unique and behavioural characteristics constitutes the definition of paediatric cortical visual impairment. Diagnostic approaches and strategies include cases history, visual acuity, refractive error, vision function assessment, ocular health and special tools.

Delayed Visual Maturation (DVM) is part of the spectrum and four types with varying characteristics and improvements over time are broadly seen:

Delayed visual maturation is of four types.

Type 1 visually impaired infants improved visual abilities by age of 6 months often without treatment

Type 2 attention problems associated with neurological or learning disability in which improvement takes longer

Type 3 children have nystagmus, albinism. Vision improves later and can improve to low normal levels

Type 4 is associated with retinal optic nerve and macular anomalies

What are the main Medical Causes of Pediatric Cortical Visual Impairment (CVI)?

Various diseases affecting brain-based visual pathways. PCVI is the end result of multiple brain diseases affecting children before, at, or after birth.

Asphyxia

Periventricular Leukomalacia (PVL)

Cerebral Vascular Accident (CVA)

Trauma, including "Shaken Baby Syndrome"

Hypoglycemia

Congenital Brain Abnormalities

Intrauterine Infections

Acquired Infections

Intra-ventricular Hemorrhage (IVH)

Post-Hemorrhagic Hydrocephalus

Kernicterus

Chromosomal Abnormalities

Infantile Spasm

Mitochondrial Diseases

Distinguishing Ocular vs. Cerebral Visual Impairment.

Ocular deals with refractive state, optics, and eye health.

Cerebral involves neuropathway problems, cortical issues, oculomotor dysfunction, and visual information processing.

Normal Vision:

Normal vision, also referred to as typical or healthy vision, is the ability of the eyes and brain to work together to process visual information accurately. This visual system is characterized by several key features:

Clear and Sharp Vision: Individuals with normal vision typically experience clear and sharp vision, meaning that they can see fine details and objects with precision. Visual acuity is typically in the normal range.

Stable Eye Movements: Normal vision is associated with stable eye movements. Both eyes work together efficiently, allowing for smooth tracking of moving objects and precise focusing.

Healthy Visual Fields: A person with normal vision usually has a healthy visual field, encompassing the entire range of what can be seen without moving the head or eyes. This includes peripheral vision, allowing for awareness of objects in the environment even when not directly focused on.

Colour Perception: Normal vision includes accurate colour perception. People can distinguish between a wide range of colours and shades.

Depth Perception: The visual system in individuals with normal vision provides reliable depth perception. This allows them to gauge distances and perceive the 3D nature of the world.

Visual Processing Efficiency: The brain efficiently processes visual information, making sense of complex scenes, patterns, and shapes without difficulty.

Cerebral Visual Impairment (CVI):

Cerebral Visual Impairment (CVI) is a neurological disorder that results from damage or dysfunction in the brain's visual processing areas. It affects the way the brain interprets visual information received from the eyes. CVI presents a set of distinctive characteristics that contrast with normal vision:

Visual Acuity Variability: In CVI, visual acuity can vary, with individuals experiencing fluctuations in their ability to see fine details. Some may have moments of clarity while others experience blurry or distorted vision.

Unstable Eye Movements: People with CVI often exhibit unstable eye movements, including nystagmus (rapid, involuntary eye movements) and strabismus (misalignment of the eyes). These eye movement abnormalities can affect their ability to focus on and track objects.

Visual Field Deficits: CVI frequently results in visual field deficits, such as hemianopia (loss of vision in one-half of the visual field) or scotomas (blind spots). These visual field abnormalities can hinder the person's awareness of objects in their environment.

Impaired Colour Perception: Individuals with CVI may struggle with colour perception. They may have difficulty distinguishing between colours or may perceive them differently

Limited Depth Perception: CVI can lead to difficulties in depth perception, making it challenging to gauge distances accurately. This can affect activities that require depth perception, such as reaching for objects or navigating the environment

Visual Processing Challenges: People with CVI often experience difficulties in processing complex visual scenes, recognizing faces, and understanding spatial relationships. They may have trouble with visual memory and visual-spatial tasks.

Variable Response to Visual Stimuli: CVI can lead to variable responses to visual stimuli. Some individuals may be hypersensitive to light or certain patterns, while others may show hyposensitivity, appearing indifferent to visual stimuli.

How is the assessment of normal vision done and how is it different from cerebral visual impairment assessment?

Assessment of Normal Vision vs. Cerebral Visual Impairment (CVI):

Assessment of Normal Vision:

Assessing normal vision typically involves a series of evaluations by eye care professionals, including ophthalmologists and optometrists. The assessment process for normal vision includes the following components:

Visual Acuity Test: This test measures the sharpness and clarity of vision. It often involves reading an eye chart from a standardized distance. Visual acuity is expressed as a fraction (e.g., 20/20) with 20/20 indicating normal vision.

Eye Health Examination: An ophthalmologist or optometrist examines the health of the eyes, checking for conditions such as cataracts, glaucoma, or retinal issues. They use various instruments and may dilate the pupils for a thorough examination.

Refraction Test: This test determines if the individual has refractive errors such as myopia (near-sightedness), hyperopia (farsightedness), or astigmatism. Based on the results, corrective lenses may be prescribed.

Colour Vision Test: To assess colour perception, tests like the Ishihara test (plates with coloured dots and numbers) or the Farnsworth-Munsell 100 hue test may be used to identify colour deficiencies like red-green colour blindness.

Visual Field Test: A visual field test, such as perimetry, checks the full extent of the visual field, identifying any blind spots or visual field deficits.

Eye Movement and Alignment Assessment: Ocular motility tests evaluate the coordination and alignment of eye movements, assessing for conditions like strabismus or nystagmus.

Assessment of Cerebral Visual Impairment (CVI):

Assessing CVI is a complex process that requires a multidisciplinary approach, often involving neurologists, ophthalmologists, and developmental specialists. The assessment of CVI differs from that of normal vision in several ways:

Functional Vision Assessment: CVI assessment focuses on functional vision, including how well an individual uses their remaining vision in daily activities. It involves observing how the person interacts with their environment and reacts to visual stimuli.

Response to Visual Stimuli: CVI assessment considers how individuals respond to various visual stimuli, including light, colours, and patterns. It assesses their reactions to different visual environments and the effectiveness of visual aids, if used.

Gaze Behaviour Assessment: Eye tracking and gaze behaviour studies may be employed to evaluate how well an individual can fixate on objects, track moving objects, and shift their gaze.

Visual Function Profile: CVI assessment often results in a visual function profile that details the individual's strengths and challenges, including specific characteristics related to visual acuity, visual field, colour perception, and visual attention.

Functional Vision Goals: The assessment may lead to the development of functional vision goals that guide interventions and support strategies to optimize the individual's use of their residual vision in daily life.

Collaborative Approach: Unlike the relatively straightforward assessments for normal vision, CVI assessment requires a collaborative approach involving various specialists to create a comprehensive understanding of the individual's visual abilities and challenges.

Challenges in Treatment:

Despite advances in understanding CVI, several challenges remain in its treatment:

Heterogeneity of Symptoms: CVI presents with a wide range of symptoms and severity levels, making it difficult to develop standardized treatment approaches.

Limited Awareness: Many healthcare professionals, educators, and even parents may lack awareness and understanding of CVI, leading to delays in diagnosis and intervention.

Individual Variability: Each person with CVI may have unique visual difficulties and strengths, requiring personalized interventions tailored to their specific needs.

Co-occurring Conditions: CVI often coexists with other neurological conditions, which can complicate the treatment process and require a comprehensive, multidisciplinary approach.

Conclusion:

Cerebral Visual Impairment is a complex condition that affects the brain's ability to process visual information. While it poses challenges in assessment and treatment, a collaborative and individualized approach involving healthcare professionals, educators, and families can make a significant difference in improving the visual functioning and quality of life for individuals with CVI. Continued research and increased awareness about CVI are vital to developing effective interventions and support systems for those affected by this condition Interdisciplinary Collaboration is encouraged for effective management of CVI and more specifically PCVI as diverse fields contribute unique perspectives.