Visual Acuity in Children PDF

Visual Acuity in Children Prepared by: Eway, Gilbero, Hernandez, Lacang Introduction: Visual Acuity - is the measure of the spatial resolution of visual processing. - Also known as resolving power of eye - Ability to differentiate two separate object as separate and appreciate the details...

Visual Acuity in Children Prepared by: Eway, Gilbero, Hernandez, Lacang Introduction: Visual Acuity - is the measure of the spatial resolution of visual processing. - Also known as resolving power of eye - Ability to differentiate two separate object as separate and appreciate the details of visible object. It is normal to find infant acuity to be lower than that if an adult. It is expected and common to find lower acuity values in the absence of any significant clinical findings. Then with growth and maturation, the test results will approach adult levels of acuity, but at different times for different techniques and different individuals. In the pediatric population, any visual acuity measurement must be considered within the context of two pieces of information: 1. What methodology was used to measure the visual acuity? 2. How old is the child?  4 Types of Visual Acuity 1. Minimum visible or detection acuity 2. Minimum separable 3. Vernier acuity (Hyperacuity) 4. Recognition acuity  1. Minimum visible or 2. Minimum separable detection acuity - Being able to tell that a given visual stimulus is - a measure of a person's ability to detect present or not, or what is the smallest stimulus an separation of contours. The smaller the individual can detect. separation of the acuity prototype elements that - Not the best descriptor of VA because of stimulus the person can resolve, the better the resolution bound (changing the strength of the stimulus you acuity. - Teller acuity cards (TAC) present square wave spatial can alter the visual acuity value). frequency gratings on a gray background matched for mean luminance in a forced choice preferential looking (FPL) paradigm. - Infants' natural attraction to striped patterns is based on their ability to distinguish between black and white stripes. If stripes become too thin, they perceive the entire area as uniform gray, indicating difficulty in resolving detail. The narrowest stripe width that still attracts the child's attention is considered their minimal separable visual acuity or spatial acuity.This measurement shows how well they can distinguish fine details. minimum separable acuity starts out poorly and improves over time  3. Vernier acuity 4. Recognition acuity (hyperacuity) - the type of acuity measurement normally used clinically on patients who are old enough to - is a measure of the eye's ability to perceive that subjectively report what they see on the typical a disalignment exists between the elements of Snellen acuity letter chart, pictures, numbers, the stimulus when compared with a stimulus and so forth. without such disalignment. - Children do this varies starts at about 2 to 2.5 - Can be measure via an FPL type paradigm years of age. where the infant will show a preference for the - Picture optotypes have higher acuity values than dis aligned square wave grating stimulus over letter or number optotypes, but recognition acuity the aligned stimulus as long as the is the most commonly used measurement on disalignment can be perceived. patients aged enough to respond. Forced Choice Preferential Looking Infants prefer fixating a patterned surface over a blank surface. Suitability Square Wave Greetings -8 weeks to 12 months -Spatial Frequency = c/deg -Patients with mental & physical disabilities -The narrower stripes -Higher SF Keeler or Teller Acuity Chart -Higher VA threshold -15 cards with black and white stripes on the right or left side. -Range c/deg -1 blank card -4mm hole in center Visually Evoked Potentials Types of VEP Flash VEP - Electrical potentials recorded from scalp in - Response to diffusely flashing light stimulus response to visual stimuli that subtends a visual field of 20 degrees. - It assesses the integrity of the visual - Cruder response than pattern VEP. pathways from the optic nerve to the occipital - Indicates that light has been perceived by cortex. cortex. Pattern Reversal VEP - Response to a patterned stimulus. - Frequency of gratings is described in CPD (cycles per degree) Pattern Onset/Offset VEP - A pattern is abruptly exchanged with an unilluminated - diffuse background. - Useful in detection of px with malingering px with nystagmus Equipment Required Properties of VEP - Visual Stimulus producing device. Amplitude - Scalp electrodes - It is the height of the wave vertical measured - Amplifier in microvolts from preceding through. - Computer and read out systems Latency - Measured in milliseconds, it is the delay Factors influencing VEP between the stimulus presentation and the peak of the wave in question. - size of stimulus - Age Patterns and Wave Form - Attention of patient Initial negative peak (N1 or N75) Large Positive peak (P1 or P100) Negative Peak (N2 or N145) Pattern and Waveform of VEP OPTOKINETIC NYSTAGMUS OKN has historically been used to assess visual acuity in infants and toddlers. By varying the width of the stripes and the distance from which they are viewed, clinicians can estimate a child's visual acuity based on the last stripe width that elicits a response. Involuntary eye movement response to moving stimuli. Used for assessing visual acuity in infants. Limited by factors such as attention and stimulus characteristics. Can be elicited in cortically blind children. 2 Phases: Smooth Pursuit Eye Movements & Contralateral Direction VERNIER ACUITY (HYPERACUITY) Vernier acuity is a form of hyperacuity that allows individuals to detect slight misalignments between two lines. This ability relies on higher-level cortical processing and is significantly more precise than standard grating acuity. In adults, Vernier acuity is about ten times better than grating acuity. Detects small misalignments; superior to grating acuity. Develops rapidly post-birth; surpasses grating acuity by three months. Indicates cortical processing capabilities. Shares developmental pathways with stereoacuity. DEVELOPMENTAL ASPECTS OF VISUAL ACUITY ➤The normal development of visual acuity follows the "Law of Improvement." ➤Early visual acuity is poor whether tested with electrophysiologic or behavioral methodologies. Gradual improvement in VISUAL ACUITY ➤Adult levels between 6 and 12 months, when VEP are used to measure the acuity, or about 3 to 5 years. DEVELOPMENTAL ASPECTS OF VISUAL ACUITY The early decreased visual acuity in the infant; 1. Foveal cone immaturities: at birth, cones are very short and stumpy with small optical apertures. 2. Cortical immaturities. 3. Incomplete myelination of the optic pathways. DEVELOPMENTAL ASPECTS OF VISUAL ACUITY At birth- foveal cones are immature and sparsely populated as compared with the adult fovea. At 15 months- the cones are only half the length of an adult cone. Approximately 4 years- The foveal cones are adult length. About 45 months - the cone density does not reach adult levels. According to Magoon and Robb That myelination progresses from central peripheral to loci. Takes more than 2 years,that the complete myelination of the optic nerve and the optic pathway. Age 3 months- Myelination of the subcortical pathways is complete. Approximately 3 years of age or later- visual acuity starts out at about 0.8 cycles per degree and gradually and steadily improves to 30 cycles per degree. According to VEP DATA- show that infant acuity reaches adult levels by 6 to 12 months. BEHAVIORAL DATA- show that FPL infant acuity reaches adult levels between 3 and 5 years of age. NATURE OR NURTURE Is the development of vision controlled by environment or genetics? NATURE OR NURTURE Nature was the school of nativism. Nurture was the school of empiricism. They studied three groups of children: 1. Healthy full term infants 2. Healthy pre-term infants 3. Full-term infants with some health abnormality which was not ophthalmologic. In other words, a child born 2 months prematurely, by chronological age 3 months will be a corrected age of 1 month, but will have 3 months of visual experience. So, this corrected aged 1-month-old child would see better than a healthy infant born at term at the age of 1 month. (This did not happen) Rather, the visual acuity development followed PCA and not chronological age. NATURE OR NURTURE ➤This clearly downplays the role of environment in the progression of visual acuity development under normal conditions. ➤ However, it is likely that environment would have a significant impact on visual acuity development. SUMMARY ➤ Visual acuity starts out poorly in the newborn infant and gradually improves over time. ➤Measurement of the acuity indicates a steady increase in function over time until the infant reaches adult acuity. ➤ This development occurs much more rapidly when assessed with electrophysiologic methodologies (VEP) than when tested with behavioral methodologies. Behavioral results, however, are probably a more accurate reflection of what the infant is actually seeing.  Infant, Toddler and Children’s Visual Acuity-Practical Aspects Teller VA Cards - Used to test visual acuity in young children and those with disabilities who can not be tested with standard letter or symbol acuity test. - Infants from 1 month to 1 year of age. - Modification of Preferential Looking Test. - Early Assessment - Amblyopia Screening - Monitoring Treatment Procedure: Types of Teller VA Cards 1. Set Up the Testing Environment Full Set (16 Cards) 2. Establish a baseline - Ideal for comprehensive visual acuity 3. Present the Teller Visual Acuity Cards assessments in infants and young children. 4. Observe the Child's Gaze Half Set (8 Cards) 5. Increase the Difficulty - used to quickly assess visual acuity and 6. Determine the finest grating detected identify potential vision problems. Teller Acuity Cards II Considerations: - widely used in clinical and research settings. Modified Teller Acuity Cards Test Distance - used for specific research purposes or for Lighting testing individuals with particular visual needs, such as those with low contrast sensitivity. Test Distance: Infants to 6 months :38 cm 7 months to 3 Years : 55 cm Older than 3 Years: 84 cm CHildren with very Poor Acuity may require an unusual close test distance between 19cm and 9.5 cm. Forced Choice Preferential Looking Procedure: Teller Acuity Card 1. Preparation - These cards utilize FPL to assess grating 2. Baseline Assessment acuity. 3. Force choices Trial Broken Wheel Test 4. Analysis 5. Interpretation - The child's preference for the broken wheel indicates their ability to detect the missing Types of FPL Tehniques: section. 1. Teller Acuity Cards Richman Paddles 2. Broken wheel Test 3. Richman Paddles - The child's preference for the smiling face indicates their ability to detect the pattern. TELLER VA CARD BROKEN WHEEL CHART RICHMAN PADDLES Looking Paddle Acuity The paddles are used in a preferential looking test, where the tester observes an infant's eye movements in response to black and white gratings. The gratings have different levels printed on the handles of the paddles, ranging from 0.25 to 8.0 cycles per centimeter of surface. Example: Lea Gratings Paddles Recommended - Children