Subjective refraction

Subjective Refraction is a technique to determine the combination of lenses that will provide the best corrected visual acuity (BCVA). It is a clinical examination used by orthoptists, optometrists and ophthalmologists to determine a patient's need for refractive correction, in the form of glasses or contact lenses. The aim is to improve current unaided vision or vision with current glasses. Glasses must also be comfortable visually. The sharpest final refraction is not always the final script the patient wears comfortably. The following equipment is used to complete a Subjective Refraction: Trial frames Trial lens box & confirmation set: Including the pinhole and occluder Jackson Cross Cylinder: a combination of two cylinders whose powers are numerically equal and of opposite sign (+/-) and whose axis are perpendicular to one another. This is used to search for astigmatism. Snellen chart Duochrome test: used to check the spherical component of the refraction Before commencing a Subjective Refraction, ensure that: The patient is seated at a 6-metre distance from the Snellen Chart. The illumination in the testing room is at a comfortable level of brightness for an indoor setting Comfortably fit the trial frames onto the patient, by adjusting the nose piece, Inter-Pupillary Distance (IPD) and vertex distance to ensure that they are properly centered. The examination begins by testing the patient's BCVA in both eyes separately, without correction. Conventionally, the right eye is tested first. An occluder is placed over the eye that is not being tested (e.g.: over the left eye, to test the right eye's vision). A pinhole occluder is then placed before the patient's eye, and their vision is then tested again (each eye separately) to determine if the patient's poor visual acuity is a result of optical irregularities, or pathological issues. If the patient is able to read more lines on the Snellen chart with the use of the pinhole, this indicates the presence of refractive error.