The psychometric prop-erties of Orbscan keratoconus detection indices. OCT combined with videokeratography to diff erentiate mild keratoconus subtypes, J Refract Surg. ![]() Elevating your knowledge of corneal topography. Videokeratographic indices to aid in screening for keratoconus. Automated keratoconus screening with corneal topogra-phy analysis. Eye surface profi ler (ESP), Eaglet Eye b.v., Lange Schaft 7 G-II, 3991 AP Houten, The Netherlands. A new method for tear fi lm stability analysis using videokera-tography Investigative Ophthalmology, Am J Ophthalmol. ![]() New York: Butterworth Heinemann 2004:17-47. Orthokeratology – Principles and Practice. Understanding its functions can greatly aid practitioners both in the characterization of the condition and the selection of a contact lens modality to best suit the patient. Though many cases of keratoconus are character-T hough we cannot rely on just one instrument, corneal topography itself can be sensitive to the earliest presentation of corneal thinning disorders, and can provide us with the ability to categorize the type of condition its severity. 16 Additionally, anomalies of global pachymetry are also highly diagnos-tic for keratoconus. Displaced corneal apices and large deviations of the visual axis (large angle Kappa) are two instances in which Placido topography, or any representations of anterior corneal surface curvature, would suggest keratoconus while elevation-based Scheimpfl ug would suggest an oth-erwise normal cornea. Conversely, some conditions or situations can result in what would appear to suggest keratoconus, when, in fact, the cornea is quite normal. This can result in what would be a false negative for keratoconus detection, if only the anterior corneal surface were ana-lyzed (such as with Placido-based corneal topography). to be normal-both in terms of curvature and elevation-but a posterior corneal elevation anom-aly still exists. Pentacam corneo-scleral profi le software. Software is under de-velopment to enable this data to be used in the virtual design of both corneal and scleral contact lenses Fig. ![]() These measure-ments can be used to detect and quantify asymmetries of scleral shape when performed in 360°. Scheimpfl ug image of a case of advanced corneo-scleral pro-keratoconus along an oblique meridian. 18 One of the newest developments in Scheimpfl ug tomog-raphy is the tech-nology’s ability to image and measure Fig. In fact, the global pachyme-try maps and both the anterior and posterior corneal elevation maps are quite typical of true keratoconus rather than pellucid. Traditionally, the classic “kissing dove” or “crab claw” pat-tern seen on curvature topography maps is considered characteristic of PMD however, because true PMD exhibits localized peripheral cor-neal thinning inferiorly 1mm from the limbus, in the majority of cases the corneal thin point on global pachymetry and corneal elevation maps is actually signifi cantly more central in regular PMD than in true PMD. 17 Scheimpfl ug tomography can also aid in the differential diagnosis of true pellucid marginal corneal de-generation. Ized by the thin point of the cornea being below that normal range of minimum corneal thickness, it is the rate of change of corneal thickness from the thin point out peripherally that is the most sensitively diagnos-tic, even in cases where the thick-ness of all points in the cornea are statistically normal. Reviews Supplements Review of Cornea & Contact Lenses May 2016:
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