Smartscope refractor5/30/2023 In soft toric or rigid front-surface toric lens fitting, a sphero-cylindrical overrefraction can assist in determining the magnitude and direction of any cylinder mislocation ( Lindsay et al., 1997).Ī repeatable cylindrical overrefraction obtained over a spherical rigid lens suggests lens flexure. If vision is inadequate following a spherical overrefraction, a sphero-cylindrical overrefraction should be performed and a toric lens fit initiated if warranted. In cases of spherical lens fitting, spherical power modifications can be demonstrated to the patient and the resultant visual acuity measured. The duochrome test is especially useful in determining the refractive end-point of an eye wearing a contact lens.Ī useful clinical technique during subjective refraction is to obtain both spherical and sphero-cylindrical end-points independently (rather than merely calculating the best-sphere refraction from the sphero-cylindrical end-point). At any aftercare visit, overrefraction can reveal required power changes due to unanticipated lacrimal lens formations, lens rotation, changes in refractive error, patient-induced lens power changes, lens warpage or lens flexure. Lastly, ocular pathology of new onset since the last visit, such as a posterior subcapsular cataract, can be easily detected by viewing the red reflex.Ī subjective sphero-cylindrical refraction over the contact lenses is an important measure that should be recorded at every visit. Distortions or small visual obstructions induced from lens deposits, scratches, warped lenses or lens lift-off from the corneal surface may also be detected during overretinoscopy. Features such as optical zone edges or bifocal segments within the entrance pupil can be observed and correlated with patient complaints. Retinoscopy can also provide invaluable information when qualitatively viewing the red reflex over the lenses. ![]() Szczotka-Flynn, Nathan Efron, in Contact Lens Practice (Third Edition), 2018 OverrefractionĪs with any subjective refraction, initial objective assessment of refractive status using an autorefractor or retinoscope provides the starting point for the subjective overrefraction. ![]() Finally, they are also more likely to break down than a retinoscope ( Steele et al. early detection of cataracts, keratoconus) provided by retinoscopy and autorefractors are typically non-portable and more expensive than retinoscopes. In addition, autorefraction lacks the assessment of the ocular media (e.g. Results can also be unreliable or unobtainable in patients with poor fixation, high refractive errors, small pupils, cataracts, pseudophakia, nystagmus, and amblyopia and in some cases age-related maculopathy ( Elliott & Wilkes 1989). ![]() However, autorefractors should not be used with young children without cycloplegia because of proximal accommodation errors producing significantly more minus results than subjective refraction ( Elliott & Wilkes 1989, Zhao et al. Finally, the high-tech nature of autorefractors can appeal to some patients. Autorefraction can be performed by clinical assistants and therefore free up a little of the optometrist's time and some autorefractors can be directly linked to an automated phoropter, so that the autorefractor result is dialled into the phoropter if required. When used with cycloplegia in children, it is as accurate, if not more so, than retinoscopy ( Elliott & Wilkes 1989, Walline et al. ELLIOTT, in Clinical Procedures in Primary Eye Care (Third Edition), 2007 4.8.2 Advantages and disadvantagesĪutorefractors provide a reliable alternative to retinoscopy in many ‘standard’ adult patients ( Elliott & Wilkes 1989, McCaghrey & Matthews 1993) and can be particularly accurate at determining astigmatism ( Walline et al.
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