Views: 1,514 | Downloads:
28
| Responses: 0
| XML | Respond to this article | Alert & updates | Request permissions | Email to a friend |
Original ArticleOpen Access
Internal Astigmatism and its Correlation to Corneal and Refractive Astigmatism
S 
Objective : To evaluate the internal astigmatism and its relationship to corneal and refrac-
tive astigmatism in a refractive surgery patient population.
Method : Patients who underwent pre-operative evaluation for Laser in situ Keratomileusis
(LASlK) at Excimer Laser Clinic, Siriraj Hospital, Mahidol University were included. Pre-operative
data including age, manifest refraction and corneal topography obtained by Orbscan Corneal Topo-
graphy were performed. Regression Analysis was done to find the correlation between refractive and
corneal astigmatism.
Results : 110 patients (220 eyes : 110 right eyes and 110 left eyes) were included. The
mean age was 31.14 เธ‘ 7.00 year (range 19 to 48 years). The mean astigmatism measured by manifest
refraction (refractive astigmatism) was 0.76 เธ‘ 0.72 diopters (range 0 to 3.50 diopters). The mean
astigmatism measured by Orbscan Corneal Topographer (corneal astigmatism) was 1.38 เธ‘ 0.72 diopters
(range 0.20 to 5.30 diopters). The mean difference in magnitude of refractive and corneal astigmatism
(internal astigmatism) was 0.62 เธ‘ 0.67 diopters (range 0 to 3.00 diopters) and 74 per cent were within
เธ‘ 1.00 diopters difference. The mean difference in axis of astigmatism was 0.95 เธ‘ 23 degree (range
0 to 85 degree) and 79.6 per cent were withinเธ‘ 15 degree difference. There was low correlation be-
tween corneal and internal astigmatism (R
2
=
0.12, p
<
0.05), also low correlation between refractive
and internal astigmatism (R2
=
0.27, p
<
0.05). There was a statistically significant difference between
magnitude of corneal and refractive astigmatism (p
<
0.05) but no difference in the axis of astigma-
tism (p
=
0.55).
Conclusion : This study demonstrated non-mutual agreement between refractive and corneal
astigmatism (presence of internal astigmatism). High value (> 1.00 diopter) of internal astigmatism
was demonstrated in 113 of the cases. Kerato-refractive surgery that attempts to correct refractive
astigmatism at corneal plane may effect long-term evaluation of the astigmatism.
Key word : Astigmatism, Cornea, Refraction
tive astigmatism in a refractive surgery patient population.
Method : Patients who underwent pre-operative evaluation for Laser in situ Keratomileusis
(LASlK) at Excimer Laser Clinic, Siriraj Hospital, Mahidol University were included. Pre-operative
data including age, manifest refraction and corneal topography obtained by Orbscan Corneal Topo-
graphy were performed. Regression Analysis was done to find the correlation between refractive and
corneal astigmatism.
Results : 110 patients (220 eyes : 110 right eyes and 110 left eyes) were included. The
mean age was 31.14 เธ‘ 7.00 year (range 19 to 48 years). The mean astigmatism measured by manifest
refraction (refractive astigmatism) was 0.76 เธ‘ 0.72 diopters (range 0 to 3.50 diopters). The mean
astigmatism measured by Orbscan Corneal Topographer (corneal astigmatism) was 1.38 เธ‘ 0.72 diopters
(range 0.20 to 5.30 diopters). The mean difference in magnitude of refractive and corneal astigmatism
(internal astigmatism) was 0.62 เธ‘ 0.67 diopters (range 0 to 3.00 diopters) and 74 per cent were within
เธ‘ 1.00 diopters difference. The mean difference in axis of astigmatism was 0.95 เธ‘ 23 degree (range
0 to 85 degree) and 79.6 per cent were withinเธ‘ 15 degree difference. There was low correlation be-
tween corneal and internal astigmatism (R
2
=
0.12, p
<
0.05), also low correlation between refractive
and internal astigmatism (R2
=
0.27, p
<
0.05). There was a statistically significant difference between
magnitude of corneal and refractive astigmatism (p
<
0.05) but no difference in the axis of astigma-
tism (p
=
0.55).
Conclusion : This study demonstrated non-mutual agreement between refractive and corneal
astigmatism (presence of internal astigmatism). High value (> 1.00 diopter) of internal astigmatism
was demonstrated in 113 of the cases. Kerato-refractive surgery that attempts to correct refractive
astigmatism at corneal plane may effect long-term evaluation of the astigmatism.
Key word : Astigmatism, Cornea, Refraction
Download:
PDF