The review found there was "limited" communication between health professionals about Child H's condition
A child went partially blind in one eye after "repeated failings" by health and social workers in Stockton-on-Tees, a serious case review found.
The report, external said the boy - known only as Child H - had an arthritic condition and developed a cataract in his left eye after missed hospital appointments.
His parents were jailed last year after admitting two counts of child neglect.
South Tees Hospitals NHS Foundation Trust admitted the harm he suffered could have been avoided.
The boy, who cannot be named for legal reasons, was diagnosed with juvenile idiopathic arthritis (JIA) at a young age. If left untreated, the condition can lead to scarring and permanent vision problems.
In 2013, when a social worker visited him, it was noted his left eye was "extremely cloudy" and his vision impaired, the review found.
A subsequent investigation involving the police revealed "extremely poor" home conditions, including rotting food and faeces smeared on his bedroom wall.
'Deeply saddened'
The boy and his sibling were later placed in local authority care.
The review found hospital and community health services "failed to communicate well or work together effectively".
Independent chair of the Stockton Local Safeguarding Children Board, Colin Morris, said: "Had they done so, the outcomes would certainly have been far more positive and this has been acknowledged by the key agencies involved."
The review concluded the boy's eye condition could have been avoided if more had been done.
South Tees Hospitals NHS Foundation Trust said it was "deeply saddened and shocked" by what had happened.
It admitted the boy had "clearly suffered harm which could have been avoided" and was working to improve systems and practices.
He is now described as a "happy and settled child" living within a family, with his vision expected to improve.
