Leigh Syndrome: A mitochondrial disorder that can present with progressive rigidity, bulbar symptoms, and visual loss, often with a history of normal development followed by decline. It's a consideration given the combination of neurological symptoms.

Multiple Sclerosis (MS): Although less common in children, MS can present with a wide range of neurological symptoms including visual loss, bulbar symptoms, and progressive rigidity. The diagnosis would depend on MRI findings and oligoclonal bands in the cerebrospinal fluid.
Acute Disseminated Encephalomyelitis (ADEM): A rare autoimmune disease that can occur after a viral infection or vaccination, presenting with multifocal neurological symptoms, which could include rigidity, bulbar symptoms, and visual disturbances.
Neuromyelitis Optica Spectrum Disorder (NMOSD): An autoimmune condition that primarily affects the optic nerve and spinal cord, leading to visual loss and other neurological symptoms. It's less common in children but should be considered.

Brainstem Tumor: Tumors in the brainstem can cause progressive neurological deficits, including rigidity, bulbar symptoms, and visual loss. Early diagnosis is crucial for treatment and prognosis.
Wernicke's Encephalopathy: Although rare in children, this condition, caused by thiamine deficiency, can lead to severe neurological symptoms including ophthalmoplegia, ataxia, and altered mental status. Prompt treatment can reverse symptoms.
Subacute Sclerosing Panencephalitis (SSPE): A rare but fatal condition caused by a persistent measles virus infection, presenting with progressive neurological deterioration, including rigidity and visual loss.

Krabbe Disease: A lysosomal storage disorder that affects the myelin sheath, leading to severe neurological symptoms, including rigidity and visual loss, typically presenting in the first year of life but can be considered in older children with atypical presentations.
Mitochondrial Myopathies: A group of disorders affecting the mitochondria, which can present with a wide range of neurological symptoms, including progressive external ophthalmoplegia, which could contribute to visual loss.
Batten Disease (Neuronal Ceroid Lipofuscinosis): A group of rare, inherited disorders that can cause progressive neurological deterioration, including visual loss, seizures, and loss of motor skills, typically presenting in early childhood.