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Vinod Maseedupally, Daniel Meoli, Bendy Nguyen, Pauline Kang, Helen A Swarbrick; Variability of ocular reference center location in normal eyes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1536.
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To determine the variability in the location of various ocular reference centers.
Ocular reference center data were collected from right eyes of 20 young normal subjects aged between 18 and 27 years. The reference centers included the geometric center (GC), corneal apex (CA), entrance pupil center (EPC) and corneal sighting center (CSC). Corneal topographic maps captured using the Medmont E300 corneal topographer (Melbourne, Australia) were used to locate GC, CA, and EPC relative to the map’s default center which is the vertex normal (VN). The GC was defined as the center of a best-fit ellipse fitted to the limbus. The CA was defined as the centroid of the steepest corneal portion on the tangential power map. The pupil center values as determined by the topographer were considered as the EPC. To determine CSC location, angle lambda was measured along the horizontal meridian only using a synoptophore (Synoptometer, Oculus, Germany) and the angle values were converted to millimeters to give the distance between EPC and CSC at the corneal plane.
The GC was located 0.33 ± 0.13 mm (range 0.12 - 0.64 mm) from the VN. All eyes showed the location of GC temporal to VN, of which the majority (16 eyes - 80%) were also located inferiorly. The CA was located at 0.84 ± 0.64 mm (0.21 - 2.25 mm) from the VN. The majority showed a temporal (15 eyes - 75%) and superior (11 eyes - 55%) location of CA. The EPC was located 0.18 ± 0.12 mm (0 - 0.46 mm) from the VN, of which the majority were located superiorly (17 eyes - 85%), and temporally (13 eyes - 65%). The CSC was located at 0.31 ± 0.15 mm (0 - 0.60 mm) nasal to the EPC.
Among various ocular reference center locations, the EPC was least variable and CA was most variable. Since CA is the reference center that governs the centration of rigid contact lenses, it is likely that lenses may tend to decenter temporally. However, decentration is likely to vary significantly between individuals. The variability in the location of CSC also highlights the importance of centering corneal reshaping procedures such as laser refractive surgery and orthokeratology to optimize visual outcomes and enhance patient satisfaction.
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