infants va

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  • 1. PresentedBy ,SONU A.S

2. The ability of a refractivity corrected eyeto discriminate fine details. Its the is the resolving power of the eye. Primary measurement tool chartintroduced in 1862 by Donders andSnellen. Visual acuity is represented by VisualAngle. Visual Angle angle made by the objectwith the nodal point of the eye. 3. Most eye problems can be treated if detectedearly. Useful in decision making. To know if visual development is normal. Helps to decide eligibility for low vision andrehabilitation services. 4. Chart illumination:luminance level of minimum 12-20 footcandles(130-215 lux). Testing Distance:generally 6 meters. 5. Response to lightAn infant will blink in response to a bright light. Pupil responseMeasuring the response of the pupil (the blackcenter part of the eye)by shining a penlight inthe eye is one way to test an infants vision. Ability to follow a targetThe most common vision acuity test in infants isa test to check their ability to look at andfollow an object or toy. 6. 1. Very soon after birth Can fix and follow a light source.2. 1 months Fixation is central, steady and maintained. Can follow a slow target.3. 3 months Binocular vision and eye coordination.4. 6months Reaches out accurately for toys.5. 9months looks for hidden toys. 7. Visual Evoked Potential (VEP) Testing. Preferential Looking Test (PLT). OptoKinetic Nystagmus (OKN) Testing. Central Steady Maintain (CSM) Method. Cat ford Drum Test. 8. Parents or caretakers are asked routinelywhether the child responds to silent smile orfollows objects around etc. 9. For those who are unable to read the letterchart, the visual evoked potential (VEP) canbe used. It measures acuity by assessing the responseof the brain to alternating black and whitestripes or checks. 10. To do the test, three small metal discs are placed on thechilds head. The discs are connected by wires to a computer. The child is then positioned in front of a TV screendisplaying alternating black and white stripes thatprogressively get narrower. As the child views the stripes, a signal is relayed fromthe eyes to the brain (the visual cortex). This signal is detected by the electrodes. The test is designed to find the finest black and whitestripes that reliably produce a response. 11. Often the vision of each eye is tested separately; apatch is used to cover the non-tested eye. The test typically takes less than an hour,depending on the childs ability to cooperate. 12. 1. Patterns reversal VEPs.2. Sweep VEPs.3. Flash VEPs. 13. The Preferential Looking test is used to assess visualacuity in infants. who are unable to identify pictures or letters. The child is presented with two stimulus fields, onewith stripes and the other with a homogeneous grayarea of the same average luminance as the stripedfield. The location of the stripes is randomly alternated. Typically, infants and children will look at the moreinteresting stripes (if they can detect them) ratherthan at the blank field. 14. Inthediagram,thebabyisshowninaninfantseat;alternatively,thechildmaysitonanadultslaporbeheldovertheshoulder.Asmall peepholeiscenteredbetweenthetwofields.Anobserverviewsthechildthroughthepeepholeandjudgesthelocationofthestripesbasedonthechildsheadandeyemovements. 15. If the child can see the stripes, he/she will prefer tolook at them. If the child cannot see them, the striped field willlook the same as the blank gray field, and the childwill not show a preference. The smallest stripe width for which the observer canconsistently identify the location of the stripes isconsidered to be the childs resolution threshold(visual acuity). 16. It is done with one eye fixation on anaccommodative target held at 40cm. C refers to the location and corneal lightreflex as the patient fixates the examinerslight under monocular conditions. S refers to steadiness of fixation onexaminers light as it is held motionless andalso as it slowly moves up. 17. M refers to the ability of the path tomaintain alignment first with one eye thenwith the other eye, as the opposite eye isuncovered. 18. OPTOKINETIC NYSTAGMUS(OKN) TESTING Nystagmus can be elicited using this test The only cooperation required in this test is that theinfant be awake and should hold both eyes open. Procedure: passing a succession of black and whitestripes through the patients field of vision. The visualangle subtended by the smallest strip width that stillelicits an eye movement is a measure of visual acuity. Its reported that OKN acuity is at least 6/120 in thenewborns and improves fairly rapidly during the first 19. CATFORD DRUM TEST It is a detection acuity test, useful in infants andpreschool children.In this test, the child is made to observe anoscillating drum with black dots of varyingsizes. The smallest dot that evokes pendular eyemovements denotes the level of visual acuity. This test is unreliable since it overestimates the 20. THANKS