Developmental Optometry - evidence-based approach on how we learn to read
How we learn to read with vision
What is Vision?
This question haunts optometry students on the first day of vision science class! Vision, in its simplest form, can be defined as the process of perceiving and interpreting light reflected from our surroundings through the human eye, enabling us to discern objects, colours, distances, and movement. This basic definition of seeing is a fundamental mechanism through which we experience the world. However, the concept of vision extends beyond this narrow definition when we consider how we use our vision every day - an aspect of a broader vision. This pertains to our ability to understand and interact with the environment around us, acknowledging not only the visible stimuli but also our position and orientation within that space.
How does vision help us learn?
Reading to learn is a multi-faceted process that relies heavily on several vision and cognitive skills. Firstly, good fixation stability is key. This involves the ability of both eyes to maintain a steady gaze on a single point, a characteristic of healthy binocular vision. Along with minimal refractive errors, clear vision allows the reader to accurately discern letters and words. Secondly, effective ocular motility skills are needed, including smooth pursuit (following words along a line) and accurate saccades (quickly shifting gaze from one line to the next). These skills facilitate efficient eye movement across the text without loss of place. Thirdly, good visual perception is required. This means the ability to correctly interpret what is seen, such as differentiating similar letters like 'b' and 'd', crucial for understanding and comprehension. Lastly, the reader must have the mental capacity to sustain these visual functions with minimal cognitive effort. This allows more cognitive resources to be allocated to understanding the content, enhancing the learning process.
Developmental Eye Testing: #2 Ocular Motility Skills
Ocular Motility skills primarily focus on Saccades and Pursuit. Saccades are rapid eye movements that shift our line of sight from one point of interest to another, such as when reading a line of text or scanning a room. A good saccade function allows for quick and precise visual fixation, critical for many daily tasks, from reading to driving. Pursuit, or smooth pursuit, on the other hand, enables the eyes to smoothly follow a moving object, maintaining the image of the object of interest on the fovea, the area of the retina where vision is sharpest. This function is vital for activities like tracking a ball in a game or following a moving car on the road. Both saccadic and pursuit eye movements play key roles in delivering a cohesive and consistent visual world. Impairments in these functions can result in difficulties in tasks like reading, playing sports, or even just navigating through the environment, emphasizing the importance of regular vision check-ups to ensure optimal eye movement health. In our clinic, we leverage the capabilities of RightEye, a computer system equipped with a built-in infrared tracker that enables us to record live eye movement during various tasks. This innovative technology delivers repeatable and quantifiable results on both saccadic and pursuit skills, providing a rich and reliable source of data.
Visual Stress Syndrome
Visual stress syndrome (Sometimes known as Irlen Syndrome) is a perceptual processing disorder characterized by difficulties with light sensitivity and visual perception. Symptoms may include eyestrain, headaches, and difficulty reading, often resulting from glare, bright lights, or certain visual patterns. While this condition is more common among neurodivergent individuals, including those with ADHD, autism, or dyslexia, it is crucial to note that it is not a cause of these conditions, but rather an associated symptom. For example, in dyslexia, the primary challenge is with language processing, not vision. Yet, many people with dyslexia also experience visual stress, leading to increased difficulties with reading and other tasks. Addressing visual stress through tailored interventions, such as color overlays or filtered lenses, can alleviate these symptoms and improve overall performance and comfort.
What’s tested in a routine eye examination
Optometrists play a critical role in maintaining ocular health by conducting comprehensive eye exams consisting of various steps. They begin with refraction, a test that helps determine an individual's glasses or contact lenses prescription. This process involves using a phoropter or trial lenses, where a series of lens choices are presented to the patient to ascertain the sharpest, clearest vision. Apart from this, the optometrist also checks ocular health. They evaluate the eye's exterior and interior, using specialized instruments to detect conditions like cataracts, glaucoma, macular degeneration, and other potential vision-threatening diseases. Furthermore, optometrists assess how well the eyes work together and may check for issues related to color vision, depth perception, and peripheral vision. These routine exams are integral in detecting and managing eye conditions that could lead to vision loss.
A developmental eye examination represents an expanded set of assessments comprehensively assessing additional visual skills/perception.
Developmental Eye Testing: #1 Binocular Vision
When testing for binocular visual function, optometrists primarily evaluate how accommodation (focusing of the eye) and vergences (inward or outward rotation of the eyes) interact. The process begins with assessing near phoria, which measures the eye's natural resting position when the binocular focus is briefly interrupted, providing insight into the balance of the eye's muscle forces. Next, the Accommodative Convergence to Accommodation (AC/A) ratio is determined, examining the relationship between accommodation and convergence during near focus. The fusional reserve test then follows, measuring the eyes' ability to maintain single vision despite the stress on the binocular vision system. The accommodation facility test evaluates the eyes' ability to rapidly change focus between near and far objects, indicative of flexibility in focusing. The Monocular Estimation Method (MEM) Retinoscopy checks for accommodative accuracy at near distances, ensuring the eyes provide clear near vision. Relative accommodation measures the maximum amount a person can change their focus while maintaining single, clear binocular vision. Lastly, the near point of convergence is determined through a push-up test, examining the closest point at which a person can maintain binocular vision. By comparing these findings to ideal parameters, optometrists can assess the efficiency of the binocular vision system and identify potential disorders.
Developmental Eye Testing: #3 Visual Perception and Motor Integration
Visual perception and motor integration work together to enable the execution of coordinated movements based on visual inputs, a crucial aspect of many daily activities, from writing and reading to playing sports. Visual-motor integration is the ability to interpret visual information and respond to it with appropriate motor actions. Essentially, it's the brain's capability to process what the eyes see, then use that information to guide the body's movements. A common method of measuring this ability involves tasks where an individual is asked to copy geometric forms or patterns. Performance on these tasks can reveal the efficiency of visual-motor integration; difficulties might present as trouble in activities requiring hand-eye coordination, such as handwriting or catching a ball. Regular assessment of visual-motor integration can help in early identification of challenges, leading to timely intervention and support, thereby ensuring optimal functional performance in daily tasks.
What services do we provide?
Our process for binocular vision testing involves the use of lenses, prisms, and retinoscope measurements. These tools may be simple, but they have been proven to yield reliable information about binocular functionality. For ocular motility measurement, we utilize the advanced RightEye eye-tracking device. This device, which is equipped with an infrared sensor, allows us to capture live eye movement as the patient carries out various tasks. Additionally, our occupational therapist (OT) performs tests for visual perception and motor integration using the Test for Visual Analysis Skills (TVAS) method.
If any issues are identified with binocular focusing or ocular motility skills, we offer vision training to help manage these symptoms. This training incorporates both modern methods, such as virtual reality-based technology, and traditional ones, like lens flippers and Brock strings.