Ocular residual and corneal astigmatism in a clinical population of high school students

Abstract

PurposeTotal refractive astigmatism is usually the first consideration that guides the selection of contact lens type (e.g., spherical or toric), while the ocular source of the astigmatism is a second, but more important consideration, for the final clinical decision. This study was conducted to provide detailed data on this topic by evaluating astigmatic components in Chinese adolescents.MethodsParticipants were recruited from healthy high school students undergoing an annual ocular examination at a local hospital. Total astigmatism (TA), corneal astigmatism (CA), and ocular residual astigmatism (ORA) were determined by a Hartmann-Shack wavefront analyzer system (KR-1W, Topcon) with the natural pupil. The axis relationship between CA and ORA was placed into three categories: on-axis, defined as an axis with a difference of 0 ± 10°; opposite-axis, a difference of 90 ± 10°; and the rest defined as oblique-axis.ResultsThe study consisted of 1,466 students (57.84% girls, age: 16.49 ± 1.05 years). ORA was present in 83.97%, 66.64%, and 45.23% of participants, according to the various criteria for astigmatism (≥ 0.50 D, ≥ 0.75 D, and ≥ 1.00 D, respectively). While with-the-rule was the most common axis orientation for both TA (76.28%) and CA (89.94%), against-the-rule predominated in ORA (93.82%; χ2 = 1688.544, p < 0.001). Opposite-axis was the major type of axis difference (90.96%) of clinical significance (i.e., ≥ 1.00 D) between CA and ORA, which also prevailed in all levels of TA (range: 56.25–82.26%).ConclusionsORA is common in high school students and usually demonstrates a compensation relationship with CA, which should be taken into consideration when determining the design of contact lenses to correct refractive error.

The components of adult astigmatism and their age‐related changes

“…The amplitude of refractive cylinder increases with age and its orientation changes from WTR to ATR ( Figure , Table ). These results are in line with earlier reports …”

“…The peak may be associated with the minimal cylinder value provided by autorefractors, however, (i.e. 0.25D) since the peak was not seen in the aberrometer based refraction data by Chen et al 46 Clinically, the gradual changes in corneal and internal astigmatism could have some minor repercussions for patients that have undergone toric cataract or refractive surgery before the age of 50 as the applied correction may not be suitable in the long term. However, since the effects reported here are relatively small and toric intraocular lens corrections are usually only implanted in eyes with more than 1D of corneal astigmatism, the long-term errors are most likely not clinically significant.…”

“…The peak may be associated with the minimal cylinder value provided by autorefractors, however, (i.e. 0.25D) since the peak was not seen in the aberrometer based refraction data by Chen et al …”

“…These results are in line with earlier reports. 1,2,7,8,[10][11][12][13][14][15]45,46 The power vector 30,31 analysis showed that both refractive vectors follow a highly leptokurtic distribution, 5,47-49 with a sharp central peak at 0D and a broader, secondary distribution at its base. Such distributions were seen before for spherical refraction, albeit that the origins of the observed shape are entirely different.…”

“…These results are in line with earlier reports. 1,2,7,8,[10][11][12][13][14][15]45,46 Figure 3. Interaction between the vector components of the anterior and posterior cornea for J 0 and J 45 (a, b); interaction between the vector components of the entire cornea and the internal optics (i.e.…”