|
The prism cover test (PCT), is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye.〔 It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components.〔 Manifest is defined by the eye deviating constantly or intermittently, where-as latent is where the deviation is normally controlled but becomes present when the eyes are dissociated.〔Ansons, A. M., & Davis, H. (2014). Diagnosis and Management of Ocular Motility Disorders (4th ed.). pp. 97. London: Blackwell.〕 A PCT reveals the total deviation and cannot distinguish between latent and manifest strabismus as you are using an alternate cover test. A number of different instruments are required when performing a PCT. These include: * Horizontal and vertical prism bars (or loose prisms).〔 * An occluder 〔 * Near accommodative target. For example, near fixation stick 〔 * Distance target.〔 For example, most commonly a Snellen chart is utilised, however the LogMAR chart is preferred as it has letters of equal legibility, same numbers of letters on each row and uniform spacing between letters and rows〔Hussain, B., Saleh, G. M., Sivaprasad, S. and Hammond, C. J. (2006). Changing from Snellen to LogMAR: debate or delay?. Clinical & Experimental Ophthalmology, 34(1), 6–8. doi: 10.1111/j.1442-9071.2006.01135.x〕 This compared to the Snellen Chart which has ‘poor reproducibility and reliability’ 〔 In order to perform a PCT, you must first perform a cover test as this gives an estimation of the size of the strabismus, thus an approximate starting point on the prism bar.〔 You can also get an indication of presence and type of strabismus by observing the patients’ eye and observing corneal reflections, also known as Hirschbergs.〔 It also shows whether the patient has a manifest or latent deviation. If a manifest deviation is present, it reveals which eye has the deviation or if it is alternating between both eyes.〔 == Indicated in == * Patients with manifest and latent strabismus 〔Ansons, A. M., & Davis, H. (2014). Diagnosis and Management of Ocular Motility Disorders (4th ed.). pp. 104-105. London: Blackwell.〕 * Patients with concomitant and incomitant deviations.〔 * Horizontal and vertical deviations 〔 * Patients with good fixation, visual acuity and cooperation 〔 * For accurate (within two prism dioptres) numerical recording that will provide a point of reference for future consultations 〔 * Monitoring the efficacy of various noninvasive treatments and also surgery interventions 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Prism cover test」の詳細全文を読む スポンサード リンク
|