C L I N I C A L
A N D
E X P E R I M E N T A L
OPTOMETRY RESEARCH PAPER
Chinese and Caucasian ocular topography and soft contact lens fit Clin Exp Optom 2016; 99: 149–156 Sheila Hickson-Curran* MCOptom FAAO Graeme Young† MPhil PhD FCOptom FAAO† Noel Brennan* PhD FAAO Chris Hunt† MSc *Johnson & Johnson Vision Care Inc., Jacksonville, Florida, USA † Visioncare Research Ltd, Farnham, United Kingdom E-mail: [email protected]
Submitted: 21 January 2015 Revised: 13 April 2015 Accepted for publication: 21 June 2015
DOI:10.1111/cxo.12336 Background: The aim was to evaluate the effect of ocular topography on soft contact lens fit in Chinese and Caucasians. Method: This study evaluated 547 subjects from two ethnic groups, Caucasian (n = 250) and Chinese (n = 297), at investigational sites in three locations: Wenzhou, China, Melbourne, Australia and Jacksonville, USA. Subjects underwent measurement of a range of ocular topographic variables using identical equipment and protocols, including: apical corneal radius (CR), corneal shape factor (CSF) in the two principal meridians, horizontal visible iris diameter (HVID), vertical palpebral aperture (PA), upper lid angle (ULA) and inter-canthal angle (ICA). Subjects were fitted with a spherical lens in two base curves (BCs) (1·Day ACUVUE, 8.50, 9.00 mm) and a toric soft lens (Accelerated Stabilization Design). Results: The steeper base curve (8.50 mm) spherical lenses gave an acceptable overall lens fit with 98 per cent or more of subjects in both groups, while the flatter lens (9.00 mm) was acceptable in a significantly higher proportion of the Chinese compared to Caucasian group (96 versus 82 per cent, p < 0.0001) . The main difference in fit between groups was for centration; there was significantly less decentration with the Chinese group (8.50 BC: 39 versus 72 per cent, p < 0.0001; 9.0 BC: 63 versus. 85 per cent, p = 0.02). The 8.5 mm base curve showed good centration (none or slight decentration) for 97 per cent of Caucasian eyes and 96 per cent of Chinese eyes. With both groups, there were some significant correlations between lens fit and ocular topographic variables, most notable between upper lid angle and toric lens orientation with the Chinese subjects. Regression analysis also showed key predictive values relating to lens fit. Conclusions: Detailed ocular measurements suggest anatomical differences between Chinese and Caucasian populations that should be considered in soft lens design. The spherical and toric lenses tested in this study fitted a large proportion of both Chinese and Caucasian eyes and are robust to the ocular differences noted.
Key words: centration, contact lenses, ocular topography, orientation, toric surface The use of contact lenses in Asia is increasing at a fast rate driven by the high prevalence of myopia coupled with increasing affluence.1 The prevalence of myopia in young people in Hong Kong, Singapore, Taiwan and urban China has been estimated at over 80 per cent.2 The usage of contact lenses in more affluent Asian countries, such as Japan and Korea, is already high and comparable with Europe.3 A number of studies of ocular topography have indicated ethnic differences, particularly between East Asian and Caucasian populations. Several reports have confirmed a tendency for smaller palpebral apertures 4–11 and smaller visible iris diameters5,6,11 in East Asians compared with Caucasians. It is believed that a better understanding of ethnic variations in anterior eye topography and its relationship with contact lens fit will allow © 2016 Optometry Australia
the development of optimised contact lenses for the Asian market. The existing literature on corneal topography is not consistent, some studies having noted steeper corneas in East Asian eyes compared to Caucasians,5,12 with others having found the reverse.8,13 In the first phase of this study, the ocular characteristics of three ethnic populations (Chinese, Japanese and Caucasian) were compared.14 On average, the Chinese corneas had similar curvature to the Caucasian but greater asphericity (more prolate shape factor) in the vertical meridian (Table 1). The Chinese also showed smaller vertical palpebral apertures, horizontal fissures and horizontal visible iris diameters (HVIDs). They also showed greater inclination (or obliquity) of the eyelids. With increasing myopia, the Chinese corneas tended to show
increasing prolate asphericity and steeper curvature. Most contact lenses from manufacturers based in the United States have been specifically designed to work across worldwide populations, although some reports have suggested that this leads to poorer fitting success rates with some ethnicities. One study involving a toric soft lens found a high proportion of loose fittings in a population of Hong Kong Chinese subjects;9 however, other studies10,15–17 of spherical soft lenses have found high levels of fitting success, including one from the same group.17 Therefore, there is some uncertainty as to whether there are clinically relevant differences in the way that soft lenses fit an Asian versus Caucasian population. The aim of this second phase of the study was to gain a better understanding of any differences in soft lens fitting characteristics between Clinical and Experimental Optometry 99.2 March 2016
149
Ocular topography and soft contact lens fit Hickson-Curran, Young, Brennan and Hunt
Caucasian
Chinese
Number of subjects
250
297
Number of eyes
500
594
31.9 (7.4)
28.0 (5.5)
18 to 45
18 to 40
Subject age (years)
Mean (SD) Range
Sex number of subjects (%)
Male Female
91 (36%)
149 (50%)
159 (64%)
148 (50%)
Sphere refraction (D)
Mean
-3.12 (2.4)
-4.97 (2.9)
Range
+7.37 to -10.87
+5.75 to -26.25
Myopic subjects
Number (%)
Cylinder refraction (D)
Mean
Cylinder axis Number of eyes (%)
236 (94%)
289 (97%)
-0.50 (0.57)
-0.44 (0.57)
Min
0.0 to -4.37
0.0 to -3.75
WTR (180° ± 20°)
125 (34%)
219 (71%)
ATR (90° ± 20°)
116 (31%)
36 (12%)
10.60 (1.44)
9.72 (1.29)
Palpebral aperture (mm)
Mean (SD)
6.6 to 14.6
6.1 to 13.4
Horizontal visible iris diameter (mm)
Mean (SD)
11.76 (0.50)
11.26 (0.43)
Range
10.6 to 13.1
10.0 to 12.6
7.78 (0.27)
7.86 (0.23)
Range
Horizontal K (mm)
Mean (SD) Range
6.92 to 8.60
7.18 to 8.49
Vertical K (mm)
Mean (SD)
7.65 (0.27)
7.67 (0.25)
Range
6.44 to 8.44
7.01 to 8.41
Mean (SD)
0.40 (0.20)
0.41 (0.19)
Horizontal corneal shape factor
Range Vertical corneal shape factor
Mean (SD) Range
Inter-canthal angle (°)
Mean (SD) Range
Upper lid angle (°)
Mean (SD) Range
Lower lid angle (°)
Mean (SD)
0.02 to 0.97
0.23 (0.16)
0.34 (0.16)
-0.84 to 0.90
0.00 to 0.81
6.32 (3.22)
7.56 (3.06)
-7.1 to 15.0
-2.2 to 15.7
3.06 (4.52)
5.96 (3.51)
-9.7 to 14.9
-5.8 to 15.5
-0.77 (3.83)
0.98 (3.35)
-10.6 to 10.4
-9.4 to 11.4
Mean (SD)
26.61 (1.50)
24.74 (1.60)
Range
22.4 to 31.5
19.0 to 28.9
Range Horizontal eyelid fissure (mm)
-0.96 to 0.94
Missing
122 (24%)
p-value
A N D
E X P E R I M E N T A L
OPTOMETRY RESEARCH PAPER
Chinese and Caucasian ocular topography and soft contact lens fit Clin Exp Optom 2016; 99: 149–156 Sheila Hickson-Curran* MCOptom FAAO Graeme Young† MPhil PhD FCOptom FAAO† Noel Brennan* PhD FAAO Chris Hunt† MSc *Johnson & Johnson Vision Care Inc., Jacksonville, Florida, USA † Visioncare Research Ltd, Farnham, United Kingdom E-mail: [email protected]
Submitted: 21 January 2015 Revised: 13 April 2015 Accepted for publication: 21 June 2015
DOI:10.1111/cxo.12336 Background: The aim was to evaluate the effect of ocular topography on soft contact lens fit in Chinese and Caucasians. Method: This study evaluated 547 subjects from two ethnic groups, Caucasian (n = 250) and Chinese (n = 297), at investigational sites in three locations: Wenzhou, China, Melbourne, Australia and Jacksonville, USA. Subjects underwent measurement of a range of ocular topographic variables using identical equipment and protocols, including: apical corneal radius (CR), corneal shape factor (CSF) in the two principal meridians, horizontal visible iris diameter (HVID), vertical palpebral aperture (PA), upper lid angle (ULA) and inter-canthal angle (ICA). Subjects were fitted with a spherical lens in two base curves (BCs) (1·Day ACUVUE, 8.50, 9.00 mm) and a toric soft lens (Accelerated Stabilization Design). Results: The steeper base curve (8.50 mm) spherical lenses gave an acceptable overall lens fit with 98 per cent or more of subjects in both groups, while the flatter lens (9.00 mm) was acceptable in a significantly higher proportion of the Chinese compared to Caucasian group (96 versus 82 per cent, p < 0.0001) . The main difference in fit between groups was for centration; there was significantly less decentration with the Chinese group (8.50 BC: 39 versus 72 per cent, p < 0.0001; 9.0 BC: 63 versus. 85 per cent, p = 0.02). The 8.5 mm base curve showed good centration (none or slight decentration) for 97 per cent of Caucasian eyes and 96 per cent of Chinese eyes. With both groups, there were some significant correlations between lens fit and ocular topographic variables, most notable between upper lid angle and toric lens orientation with the Chinese subjects. Regression analysis also showed key predictive values relating to lens fit. Conclusions: Detailed ocular measurements suggest anatomical differences between Chinese and Caucasian populations that should be considered in soft lens design. The spherical and toric lenses tested in this study fitted a large proportion of both Chinese and Caucasian eyes and are robust to the ocular differences noted.
Key words: centration, contact lenses, ocular topography, orientation, toric surface The use of contact lenses in Asia is increasing at a fast rate driven by the high prevalence of myopia coupled with increasing affluence.1 The prevalence of myopia in young people in Hong Kong, Singapore, Taiwan and urban China has been estimated at over 80 per cent.2 The usage of contact lenses in more affluent Asian countries, such as Japan and Korea, is already high and comparable with Europe.3 A number of studies of ocular topography have indicated ethnic differences, particularly between East Asian and Caucasian populations. Several reports have confirmed a tendency for smaller palpebral apertures 4–11 and smaller visible iris diameters5,6,11 in East Asians compared with Caucasians. It is believed that a better understanding of ethnic variations in anterior eye topography and its relationship with contact lens fit will allow © 2016 Optometry Australia
the development of optimised contact lenses for the Asian market. The existing literature on corneal topography is not consistent, some studies having noted steeper corneas in East Asian eyes compared to Caucasians,5,12 with others having found the reverse.8,13 In the first phase of this study, the ocular characteristics of three ethnic populations (Chinese, Japanese and Caucasian) were compared.14 On average, the Chinese corneas had similar curvature to the Caucasian but greater asphericity (more prolate shape factor) in the vertical meridian (Table 1). The Chinese also showed smaller vertical palpebral apertures, horizontal fissures and horizontal visible iris diameters (HVIDs). They also showed greater inclination (or obliquity) of the eyelids. With increasing myopia, the Chinese corneas tended to show
increasing prolate asphericity and steeper curvature. Most contact lenses from manufacturers based in the United States have been specifically designed to work across worldwide populations, although some reports have suggested that this leads to poorer fitting success rates with some ethnicities. One study involving a toric soft lens found a high proportion of loose fittings in a population of Hong Kong Chinese subjects;9 however, other studies10,15–17 of spherical soft lenses have found high levels of fitting success, including one from the same group.17 Therefore, there is some uncertainty as to whether there are clinically relevant differences in the way that soft lenses fit an Asian versus Caucasian population. The aim of this second phase of the study was to gain a better understanding of any differences in soft lens fitting characteristics between Clinical and Experimental Optometry 99.2 March 2016
149
Ocular topography and soft contact lens fit Hickson-Curran, Young, Brennan and Hunt
Caucasian
Chinese
Number of subjects
250
297
Number of eyes
500
594
31.9 (7.4)
28.0 (5.5)
18 to 45
18 to 40
Subject age (years)
Mean (SD) Range
Sex number of subjects (%)
Male Female
91 (36%)
149 (50%)
159 (64%)
148 (50%)
Sphere refraction (D)
Mean
-3.12 (2.4)
-4.97 (2.9)
Range
+7.37 to -10.87
+5.75 to -26.25
Myopic subjects
Number (%)
Cylinder refraction (D)
Mean
Cylinder axis Number of eyes (%)
236 (94%)
289 (97%)
-0.50 (0.57)
-0.44 (0.57)
Min
0.0 to -4.37
0.0 to -3.75
WTR (180° ± 20°)
125 (34%)
219 (71%)
ATR (90° ± 20°)
116 (31%)
36 (12%)
10.60 (1.44)
9.72 (1.29)
Palpebral aperture (mm)
Mean (SD)
6.6 to 14.6
6.1 to 13.4
Horizontal visible iris diameter (mm)
Mean (SD)
11.76 (0.50)
11.26 (0.43)
Range
10.6 to 13.1
10.0 to 12.6
7.78 (0.27)
7.86 (0.23)
Range
Horizontal K (mm)
Mean (SD) Range
6.92 to 8.60
7.18 to 8.49
Vertical K (mm)
Mean (SD)
7.65 (0.27)
7.67 (0.25)
Range
6.44 to 8.44
7.01 to 8.41
Mean (SD)
0.40 (0.20)
0.41 (0.19)
Horizontal corneal shape factor
Range Vertical corneal shape factor
Mean (SD) Range
Inter-canthal angle (°)
Mean (SD) Range
Upper lid angle (°)
Mean (SD) Range
Lower lid angle (°)
Mean (SD)
0.02 to 0.97
0.23 (0.16)
0.34 (0.16)
-0.84 to 0.90
0.00 to 0.81
6.32 (3.22)
7.56 (3.06)
-7.1 to 15.0
-2.2 to 15.7
3.06 (4.52)
5.96 (3.51)
-9.7 to 14.9
-5.8 to 15.5
-0.77 (3.83)
0.98 (3.35)
-10.6 to 10.4
-9.4 to 11.4
Mean (SD)
26.61 (1.50)
24.74 (1.60)
Range
22.4 to 31.5
19.0 to 28.9
Range Horizontal eyelid fissure (mm)
-0.96 to 0.94
Missing
122 (24%)
p-value
