A method of controlling a visual therapy video game in response to user eye movements, the method comprising: rendering a video game on a head mounted display by a computing system , the head mounted display including a first display for the left eye and a second display for the right eye; tracking a user's eye movements in response to rendering of the video game on the head mounted display, said tracking comprising (i) capturing images of a left eye of the user by a first image capturing device disposed proximate to the first display, (ii) capturing images of a right eye of the user by a second image capturing device disposed proximate to the second display, and (iii) outputting the positions of the left and right eyes to the computing system; controlling, via the computing system, a response of the video game based on accommodative and proximal vergence of the user's eyes; determining peak velocity differences between a left eye and a right eye of the user, characterised by rending stimuli of the video game to asymmetrical stimulate the left eye or the right eye of the user via the video game based on peak velocity differences between the left and right eyes dynamically adjusting a magnitude of asymmetrical stimulation advancement in the visual therapy video game to limit visual suppression; advancing the visual therapy game based on a detection that the left and right eyes of the user have fused on visual stimuli in the visual therapy video game based on the images captured by the first and second capturing devices and the head mounted display output of the positions of the right and left eyes; progressing the visual therapy video game from a first level of difficulty to a second level of difficulty based on a detected gain in vergence based on the images captured by the first and second capturing devices and the head mounted display output of the positions of the right and left eyes, wherein the second level of difficulty is more challenging than the first level of difficulty. rendering a video game on a head mounted display by a computing system , the head mounted display including a first display for the left eye and a second display for the right eye; tracking a user's eye movements in response to rendering of the video game on the head mounted display, said tracking comprising (i) capturing images of a left eye of the user by a first image capturing device disposed proximate to the first display, (ii) capturing images of a right eye of the user by a second image capturing device disposed proximate to the second display, and (iii) outputting the positions of the left and right eyes to the computing system; controlling, via the computing system, a response of the video game based on accommodative and proximal vergence of the user's eyes; determining peak velocity differences between a left eye and a right eye of the user, characterised by rending stimuli of the video game to asymmetrical stimulate the left eye or the right eye of the user via the video game based on peak velocity differences between the left and right eyes dynamically adjusting a magnitude of asymmetrical stimulation advancement in the visual therapy video game to limit visual suppression; advancing the visual therapy game based on a detection that the left and right eyes of the user have fused on visual stimuli in the visual therapy video game based on the images captured by the first and second capturing devices and the head mounted display output of the positions of the right and left eyes; <EOS>