Duke-elder Refraction 10th Edition Pdf Free Download
Leon Marcellus
Background: Refractive errors in children should be identified and corrected as early as possible to prevent irreversible vision loss. Therefore, accurate methods of objective refraction should be employed by paediatric eye care providers when examining young children. The purpose of this study was to assess the accuracy of non-cycloplegic and cycloplegic retinoscopy and autorefractometry as objective methods of refraction, and to determine their suitability with subjective acceptance.
Methods: The one-year study included 453 children of 3-15 years. Noncycloplegic autorefraction and streak retinoscopy were done. These were followed by cycloplegic autorefraction and streak retinoscopy. Cycloplegia was attained by using atropine sulphate 1% eye drops and cyclopentolate hydrochloride 1% eyedrops for children of 3-7 years and 8-15 years respectively. Postmydriatic subjective refraction was then done. Results were compared using Analysis of Variance (ANOVA). Calculated p
Results: Noncycloplegic methods showed underestimation of hypermetropia and overestimation of myopia. The spherical and cylindrical measurements of cycloplegic autorefraction were equivalent to cycloplegic retinoscopy. Axis of cycloplegic autorefraction was better than cycloplegic retinoscopy.
Conclusions: The most accurate method of objective refraction is cycloplegic retinoscopy. However, the spherical and cylindrical measurements of cycloplegic autorefraction can be substituted for conventional cycloplegic retinoscopy in young children.
Deepikadevi S, Sundararajan D, Namitha K, Murali K. Comparing the effect of conventional method of retinoscopic refraction with computerized automated refraction in various refractive error patients. Int Arch Integr Med. IJAM. 2017;4(10):104-10.
Rotsos T, Grigoriou D, Kokkolaki A, Manios N. A comparison of manifest refractions, cycloplegic refractions and retinoscopy on the RMA-3000 autorefractometer in children aged 3 to 15 years. Clin Ophthalmol. 2009;2009:429-31.
Background: Uncorrected refractive error is the most common cause of visual impairment globally. Yet, there is paucity of refractionists in rural areas of most developing countries. Thus, there is a need for a cost effective but accurate method of refraction that could be used by rural health workers with minimal training. To compare refractive error measurements of autorefractor with that of focometer with a view to determining the accuracy and reliability of focometer. Methods: This was a comparative cross-sectional study conducted among patients with refractive errors attending the Guinness Eye Centre Clinic, Lagos University Teaching Hospital, Lagos, Nigeria. Consecutively consenting patients who met the eligibility criteria were recruited until the sample size was attained. All participants had a standardized protocol examination including visual acuity assessment and ocular examination. Refractive error was measured using the autorefractor, focometer and subjective refraction in both eyes of each participant. Comparison was done based on the means of variables of autorefractor, subjective refraction and focometer measurements using the paired-sample t-tests, Pearson's correlation and linear regression. Agreement between the measurements was investigated using the Bland-Altman analysis and reliability of the repeated measurements tested with Cronbach's alpha. The analysis was considered statistically significant when the P < 0.05. Results: Four hundred eyes of 200 patients were analyzed in this study. The mean age of respondents was 45.1 [+ or -] 16.3yrs and the male:female ratio was 1: 2.1. There was a statistically significant difference between the mean spherical (P < 0.001) and cylindrical (P < 0.001) readings of the focometer and autorefractor. However, the mean difference between the spherical equivalent of focometer and that of the autorefractor was not statistically significant (P = 0.66). Pearson correlation coefficient was high for the compared methods of refraction as both the bivariate linear regression between the autorefractor and focometer, and that between the subjective refraction and focometer showed good linearity. Bland-Altman plot showed good agreement between the mean focometer measurements with both the autorefractor (mean difference = +0.02 [+ or -] 0.85 DS; mean difference [+ or -] 1.96 standard deviation [SD] = 1.69 to - 1.65 DS) and subjective refractive (mean difference = +0.06 [+ or -] 0.72 DS; mean difference [+ or -] 1.96 SD = 1.49 to - 1.36 DS) measurements. Cronbach's alpha showed good reliability of focometer and autorefractor repeated measurements. Conclusion: This study showed a good correlation and agreement between focometer and autorefractor. Hence, focometer could be used for refraction in low resource settings where locals could be trained in its use.
Given that the patient's blood glucose and A1c were noted to be recently elevated at 163 and 12.6% respectively, and increased from his prior measurements of 128 and 8.0%, the most likely diagnosis was hyperopic shift due to diabetic induced lenticular changes. As mentioned above, no abnormalities of the cornea, lens, or retina were found on exam or during diagnostic work-up. He denied an inciting traumatic event, and while certain medications, such as antihistamines, can cause hyperopic shift, this patient denied use of these medications. Given the lack of concerning features on exam and his markedly elevated A1c, we elected to proceed with close observation with frequent monitoring of visual acuity, manifest refractions, and A1c (Figure 3). We encouraged better blood glucose control and agreed with the recent addition of long acting insulin. Over the course of the next 2 months his A1c dropped to 7.2% and his manifest refraction returned to his baseline. (Figure 4).
Of note, the refractive power of the lens is dependent upon many factors including it's thickness, curvature, and refractive index [3]. Additionally, the refractive power is affected by the osmotic gradient across the lens capsule, which determines the distribution of water within different parts of the lens. In regards to index of refraction, one should refer to Snell's law for further understanding of the concept. Snell's law states that if light passes from a medium with a lower index of refraction to one of higher index of refraction, it will be bent towards the normal. If light passes from a medium with a higher index of refraction to one of lower index of refraction, it will be bent away from the normal. This relationship is described using the equation:
where n1 is the refractive index of the first medium the light passes through, with Θ1 representing the angle of incidence of the light ray, and n2 is the refractive index of the second medium with Θ2 being the angle of refraction of the light.
In the human eye, the average index of refraction of the crystalline lens is 1.386, which is higher than the index of refraction of the aqueous 1.336. This difference helps drive the refractive power of the crystalline lens. If the refractive index of the lens increases, light undergoes more refraction; thus, a myopic shift will occur. If the refractive index of the lens decreases, light undergoes less refraction; thus, a hyperopic shift will occur (Figure 6).
Tham, Mathilda and Jones, Hannah. 2008. 'Metadesign Tools: Designing the seeds for shared processes of change'. In: Changing the Change: Design, Visions, Proposals and Tools. Proceedings. Turin, Italy 10th - 12th July 2008.[Conference or Workshop Item]
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