Visually impaired patient tend to have high prevalence of uncorrected refractive error. A good refraction is likely to yield a substantial improvement in visual acuity. Objective refraction either by retinoscopy or by autorefractometer may not be possible in many cases of media opacity, optical irregularities, pupil size and location. Therefore subjective refraction is more important in such cases. Use hand held trial frame and trial lenses rather than phoropter as it will allow eccentric head and eye position, most patient would like to acquire. Also try larger changes of lenses, allow time to read the chart.
Don’t even hesitate to change the distance between the patient and the chart. Keratometer may help to get the baseline astigmatic correction. Repeated presentation to certain patient may be necessary to yield satisfactory results. Significant refractive error may be associated with certain ocular condition like albinism, retinitis pigmentosa, corneal scarring. The high astigmatic error that occurs nearly in all cases of albinism is usually accompanied by myopia or hyperopia. Patient with retinitis pigmentosa may have normal or near to normal central vision until cataract or macular changes occur.
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| Fig:- Retinitis Pigmentosa |
Pathological myopia is generally assumed to be caused by the developmental failure of one of the ocular components. High astigmatism greater than 5.00 D is most often a form of irregular astigmatism.
High hyperopia is generally associated with refractive amblyopia with no subjective complains. The practitioner must be alert for these deviations from the routine norms in order to diagnose and manage the high ametropic patient.
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