Main Article Content
Background and Objective
To determine the relationships between corneal and scleral elevation topography in subjects with corneal ectasias and normal corneas.
Material and Methods
This is a multi-site retrospective study. Ocular surface topography (sMap3D, Precision Ocular Metrology, US) was collected on 115 eyes with prolate cornea profile (Group A) and 227 eyes showing corneal ectasia (Group B). Sagittal height (SAG 1) was measured in the axis of the highest elevated point of the cornea (apex), defined by the meridian joining this apex to the geometrical center of the cornea at an 16 mm chord diameter (8-mm radius). Another sag value was evaluated 180° away (SAG 2) at the same diameter/radius. The difference in height between SAG 1 and SAG 2 represents a quadrant specific effect (QSE). Conjunctival toricity is estimated by comparing the best fit of the conjunctival/scleral shape data to a toric (Sin2) curve; the root- mean-squared error (RMSE) of this curve, a measure of irregularity, was also calculated.
The ectasia subjects demonstrated greater QSE, (p<0.001), standard toricity (p<0.001) and RMSE (p<0.001) on the sclera compared to normal cornea cases. If the apex of the ectasia was ≥1.25mm from the corneal center, the asymmetry was greater. Within the Group A, standard toricity was significantly higher than QSE (p<0.001) suggesting a more regular conjunctival pattern. As a proof, a significantly greater proportion of cases in Group B vs. Group A (57% vs. 26%, p<0.001) were found with conjunctival irregular shape, as previously defined. In both groups, subjects graded as having spherical/toric scleral shape had significantly lower RMSE values than those graded as having irregular shapes (p<0.001).
Subjects with corneal ectasia have a different scleral shape compared to those with normal corneal profiles, largely presenting as a quadrant specific effect along the same axis. This difference is higher if the apex of the ectasia is ≥1.25 mm from the corneal center. RMSE seems to correlate with scleral shape classification in both groups.
2. Consejo A, Llorens-Quintana C, Bartuzel MM, Iskander DR, Rozema JJ. Rotation asymmetry of the human sclera. Acta Ophthalmol 2019;97(2)e266–e270
3. DeNaeyer G, Sanders D, van der Worp E, et. al. Qualitative assessment of scleral shape patterns using a new wide field ocular surface elevation topographer. J Cont Lens Res Sci 2017;1(1):12–22. http://www.jclrs.org/index.php/JCLRS/article/view/11/4
4. Kinoshita, B, Morrison, S, Caroline, P. Corneal toricity and scleral asymmetry…are they related? Poster GSLS 2016; January 21-24, Las Vegas, USA.
5. Siebert, S, Jedlicka, J. Utilizing corneal topography to aid in predicting scleral topography for the purpose of fitting scleral contact lenses. Poster GSLS 2017; January26-29, Las Vegas, USA.
6. Consejo, A, Rozema, JJ. Scleral Shape and its correlations with corneal astigmatism. Cornea 2018 Aug;37(8):1047–52.
7. Macedo-de-Araújo, RJ, Amorim-de-Sousa, A, Queirós, A, et. al. Relationship of placido corneal topography data with scleral lens fitting parameters. Cont Lens Anterior Eye 2018 Jul 25 [Epub ahead of print].
8. Piñero DP, Martínez-Abad A, Soto-Negro R, et. al. Differences in corneo-scleral topographic profile between healthy and keratoconus corneas. Cont Lens Anterior Eye 2018 May 22 [Epub ahead of print]
9. Visser ES, Visser R, Van Lier HJ. Advantages of toric scleral lenses. Optom Vis Sci.Optom Vis Sci.Optom Vis Sci 2006;Apr;83(4):233–6.
10. Visser ES, Visser R, van Lier HJ, Otten HM. Modern scleral lenses part II: patient satisfaction. Eye Contact Lens 2007;Jan;33(1):21–5.
11. Visser ES1, Van der Linden BJ, Otten HM, Van der Lelij A, et. al.. Medical applications and outcomes of bitangential scleral lenses. Optom Vis Sci 2013 Oct;90(10):1078–85
12. Morrison, S. Schwartz, B, DeNaeyer, G, Sanders, D, Management of corneo-scleral irregularities with virtually designed custom multi-meridian scleral lenses. Poster Am Acad Optom 2017; October 11-14 Chicago, IL
13. Marriott, P.J. An analysis of the global contours and haptic contact lens fitting, Br JPhysiol Opt 1966;23:1–40.