EyeWitness

Spring 2017

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16 CLSA EyeWitness Spring 2017 impact the opportunity to fully de- velop normal vision in a young child. The smaller image size that is due to the vertex distance of spectacles may be better managed with a contact lens that has a vertex distance of zero thus providing a larger image. This larger image size may increase best-corrected vision. Nystagmus Nystagmus is a condition in which the eyes make repetitive, uncontrolled movements, often resulting in reduced vision. These involuntary eye move- ments can occur from side to side, up and down, or in a circular pattern. As a result, both eyes are unable to hold steady on objects being viewed. Un- usual head positions and head nod- ding in an attempt to compensate for the condition may accompany nystag- mus. Most individuals with nystagmus can reduce the severity of their uncon- nea is best managed with a contact lens. This condition is to be considered ur- gent if the patient is of a young age. The eye may forever lose the opportunity to be corrected as the resultant amblyopia develops over a short period of time. By neutralizing the corneal irregularities with a contact lens, the eye of a young child will possibly gain enough visual improvement to avoid the potential per- manent loss. lens wear found in the CLIP study, over the three-year study period, there were only 13 adverse events among 9 sub- jects. In addition, the ACHIEVE study found very similar rates of myopic pro- gression in both groups of patients over the three-year period (1.08D spectacle group and 1.27D contact lens group). Fitting pediatric patients is not usu- ally about routine visits and patients who "want to" wear contact lenses. It is about critical and often urgent situa- tions and patients who "have to" wear contact lenses. The more common medical indications for contact lenses can be categorized into three groups – anisometropia, irregular corneal astig- matism and "large" refractive errors. Anisometropia One of the more common condi- tions potentially leading to a perma- nent loss of vision in a young patient is anisometropia. This difference in the refractive errors of the two eyes can lead to suppression of the less clear image. As a result of the non-focused eye, the brain of a young patient simply turns off the blurred eye. Early detection is key to successful treatment. Following the diagnosis of this problem being present, simply correcting the refrac- tive error may be enough. However, it has been reported that small differences between the refractive errors of the two eyes corrected with spectacles and the resultant anisokonia can lead to foveal suppression impacting stereopsis and depth perception. The use of a contact lens or con- tact lenses alters the effective image size due to the vertex distance being zero compared to either the magnification or minification of the image size due to the vertex distance with spectacles. One of the most severe examples of this condition would be a child with a unilat- eral congenital cataract corrected with spectacles postoperatively. Irregular Corneal Astigmatism Whether acquired or congenital, the presence of irregular corneal astig- matism of the anterior curve of the cor- Obviously, patching the better eye may also be necessary if the treat- ed eye's vision is not as correctable as the unaffected eye. The length of time the child is to be patched is to be deter- mined by the pediatric ophthalmologist or optometrist, as this area of treatment is sometimes controversial. The factors that are considered include the level of vision obtained, age of the child and the condition of the fellow eye. Large Refractive Errors The optics of spectacle correction in high powers have inherent properties that include distortion, prismatic ef- fect and minification / magnification. For instance, the decrease in image size when one views an object through high minus spectacles may result in less vi- sion. This decrease in image size may trolled eye movements and improve vision by positioning their eyes to look to one side. This is called the "null point" where the least amount of nys- tagmus is evident. To accomplish this, they may need to adopt a specific head posture to make the best use of their vi- sion. The direction of nystagmus is de- fined by the direction of its quick phase (e.g., a right-beating nystagmus is char- acterized by a rightward-moving quick phase, and a left-beating nystagmus by a leftward-moving quick phase). The oscillations may occur in the ver- tical, horizontal or torsional planes, or in any combination. The resulting nystagmus is often named as a gross description of the movement, e.g., downbeat nystagmus, upbeat nystag- mus, seesaw nystagmus, periodic alter- nating nystagmus. Having nystagmus Fitting pediatric patients is not usually about routine visits and patients who "want to" wear contact lenses. It is about critical and often urgent situations and patients who "have to" wear contact lenses.

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