근시성 굴절교정수술안의 각막 중심부 및 주변부의 비구면도 = Asphericity of the Central and Peripheral Cornea in Myopic Laser Refractive Surgery Patients

국문 초록 (Abstract)

목 적: 근시성 각막굴절교정 수술안에서 각막 중심부 및 주변부의 비구면도를 정시안과 비교하고 수술전 등가구면굴절력과의 상관성을 관찰하고자 하였다.
방 법: 근시성 각막굴절교정수술을 받고 정시상태가 된 135안(평균 23.49±2.5세, 범위 20~29세)과 정시안 40안(평균 22.50±1.7세, 범위 20~25세)을 대상으로 Pentacam (Oculus Inc., Germany) 각막형태 검사기기를 사용하여 각막 6mm, 7mm, 8mm, 9mm, 10mm 영역의 비구면계수 Q값을 측정하였고, 수술안은 수술 전 등가구면굴절력이 -6.00D 미만은 수술안 그룹 1(평균 -4.41±1.09D, 범위 -1.25~-5.58D)과 -6.00D 이상은 수술안 그룹 2(평균 -7.12±0.95D, 범위 -6.00~-9.00D)로 분류하여 비교 분석하였다.
결 과: 정시안의 비구면계수 Q값은 모든 각막 영역에서 negative 값으로 영역에 따라 -0.34±0.12(6mm 영역)에서 -0.52±0.09(10mm 영역)로 주변부 영역으로 갈수록 negative 값은 더 커졌고, 수직경선이 수평경선보다 더 큰 negative 값을 보였다. 그러나, 근시성 각막굴절교정 수술안의 비구면계수 Q값은 모든 각막 영역에서 positive 값으로 영역에 따라 0.84±0.43(6mm 영역)에서 0.09±0.30(10mm 영역)으로 주변부로 갈수록 positive 값이 감소하였으며, 각막의 8mm 영역까지는 수직경선이 수평경선보다 positive 값이 더 컸지만, 9mm와 10mm 영역에서는 수평경선이 수직경선보다 positive 값이 더 크게 나타났다. 비구면계수 Q값은 각막의 6mm, 7mm, 8mm 영역에서 수술 전 등가구면굴절력과 높은 상관성을 보였다(각각, R=-0.725, R=-0.744, R=-0.713, p=0.000).
결 론: 근시성 굴절교정 수술안의 각막형상은 prolate 형태에서 oblate 형태로 변화되며 비구면계수 Q값은 negative 값에서 positive 값으로 변하고, 각막의 경선에 따른 비구면 계수도 정시안과 다른 양상을 보였다. 이와 같은 각막형상의 변화는 안광학적 시기능 변화의 예측과 근시성 각막굴절교정 수술안을 위한 시력교정용 콘택트렌즈 설계 및 피팅에 필요한 기초자료를 제공할 것으로 사료된다.

다국어 초록 (Multilingual Abstract)

Purpose: To evaluate changes in asphericity (Q-value) of the central and peripheral cornea in myopic corneal refractive surgery group compared with emmetropes and correlation between pre-operative refractive error (spherical equivalent) and Q-value of post-operation.
Methods: One hundred thirty five eyes of 68 subjects (23.49±2.5 years, range 20 to 29) who underwent myopic refractive surgery and 40 eyes of 20 emmetropes (22.50±1.7 years, range 20 to 25) were enrolled. Q-value was measured using a Pentacam Oculyzer topography (Oculus Inc., Germany) for 6mm to 10mm zones. For analysis of post-op group, the group was classified by pre-op spherical equivalents of < -6.00 D(-4.41±1.09D, range -1.25 to -5.58) and ≥-6.00D (-7.12±0.95D, range -6.00 to -9.00) as two post-op groups.
Results: The mean Q-values in the emmetropes ranged between -0.34±0.12 (6mm zone) to -0.52±0.09 (10mm zone). There was a tendency to become more negative Q-values toward the peripheral zone. The negative Q-values with vertical meridian were greater than those with horizontal meridian in all diameters measured along the corneal meridian. However, the mean Q-values in post-op group ranged between 0.84±0.43 (6mm zone) to 0.09±0.30 (10mm zone). There was a tendency for Q-values to become less positive Q-values toward the peripheral zone. The positive Q-values with vertical meridian in the post-op group were more than those with horizontal meridian in 6mm, 7mm and 8mm zones measured along the corneal meridian. Whereas, the positive Q-values with vertical meridian in the post-op group were lower than those with horizontal meridian in 9mm and 10mm zones. There was a tendency for Q-values to become more positive with increased pre-op spherical equivalent (P=0.000) and significant correlation between Q-value and pre-op refractive error in 6mm, 7mm and 8mm zones (R=-0.725, R=-0.744 and R=-0.731, respectively).
Conclusions: Q-value was changed from prolate cornea (negative Q-value) to oblate cornea (positive Q-value) in myopic corneal refractive surgery group compared with emmetropes and Q-value according to corneal meridian in post-op group found to be different patterns compared with emmetropes. These changes in Q-value would be provided basic data for outcome of visual performance and for contact lens design and fitting in eyes with a new anatomical configuration induced by corneal refractive surgery.

참고문헌 (Reference)

1 전인철, "측정 범위에 따른 각막비구면계수의 비교" 한국안광학회 17 (17): 469-476, 2012

2 Alió JL, "Topography-guided laser in situ keratomileusis (TOPOLINK) to correct irregular astigmatism after previous refractive surgery" 19 (19): 516-527, 2003

3 Eghbali F, "Topographic determination of corneal asphericity and its lack of effect on the relative outcome of radial keratotomy" 119 (119): 275-280, 1995

4 Holladay JT, "Topographic changes in corneal asphericity and effective optical zone after laser in situ keratomileusis" 28 (28): 942-947, 2002

5 Dubbelman M, "The shape of the anterior and posterior surface of the aging human cornea" 46 (46): 993-1001, 2006

6 Holladay JT, "The relationship of visual acuity, refractive error, and pupil size after radial keratotomy" 109 (109): 70-76, 1991

7 Kiely PM, "The mean shape of the human cornea" 29 (29): 1027-1040, 1982

8 Mandell RB, "The enigma of corneal contour: Everett Kinsey Lecture" 18 (18): 267-273, 1992

9 Spadea L, "Role of the corneal epithelium in refractive changes following laser in situ keratomileusis for high myopia" 16 (16): 133-139, 2000

10 Chayet AS, "Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia" 105 (105): 1194-1199, 1998

11 Marcos S, "Optical response to LASIK surgery for myopia from total and corneal aberration measurements" 42 (42): 3349-3356, 2001

12 Atchison DA, "Optical design of intraocular lenses. I. On-axis performance" 66 (66): 492-506, 1989

13 Yamane N, "Ocular higher-order aberrations and contrast sensitivity after conventional laser in situ keratomileusis" 45 (45): 3986-3990, 2004

14 Moreno-Barriuso E, "Ocular aberrations before and after myopic corneal refractive surgery: LASIKinduced changes measured with laser ray tracing" 42 (42): 1396-1403, 2001

15 Townsley MG, "New knowledge of the corneal contour" 13 (13): 38-43, 1970

16 Mandell RB, "Methods to measure the peripheral corneal curvature. Part two: geometric construction and “computers”" 33 : 585-589, 1962

17 Pallikaris IG, "Induced optical aberrations following formation of a laser in situ keratomileusis flap" 28 (28): 1737-1741, 2002

18 Oshika T, "Higher order wavefront aberrations of cornea and magnitude of refractive correction in laser in situ keratomileusis" 109 (109): 1154-1158, 2002

19 Miller JM, "Higher order aberrations in normal, dilated, intraocular lens, and laser in situ keratomileusis corneas" 18 (18): S579-S583, 2002

20 Holladay JT, "Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography" 25 (25): 663-669, 1999

21 Jiménez JR, "Equation for corneal asphericity after corneal refractive surgery" 19 (19): 65-69, 2003

22 Lindsay R, "Descriptors of corneal shape" 75 (75): 156-158, 1998

23 Read SA, "Corneal topography with Scheimpflug imaging and videokeratography: comparative study of normal eyes" 35 (35): 1072-1081, 2009

24 Carney LG, "Corneal topography and myopia: A crosssectional study" 38 (38): 311-320, 1997

25 Fleming JF, "Corneal asphericity and visual function after radial keratotomy" 12 (12): 233-240, 1993

26 Bottos KM, "Corneal asphericity and spherical aberration after refractive surgery" 37 (37): 1109-1115, 2011

27 Sheridan M, "Corneal asphericity and refractive error" 9 (9): 235-238, 1989

28 Schwiegerling J, "Corneal ablation patterns to correct for spherical aberration in photorefractive keratectomy" 26 (26): 214-221, 2000

29 Alió JL, "Contact lens fitting to correct irregular astigmatism after corneal refractive surgery" 28 (28): 1750-1757, 2002

30 Holmes-Higgin DK, "Characterization of the aspheric corneal surface with intrastromal corneal ring segments" 15 (15): 520-528, 1999

31 González-Méijome JM, "Asphericity of the anterior human cornea with different corneal diameters" 33 (33): 465-473, 2007

32 Liou HL, "Anatomically accurate, finite model eye for optical modeling" 14 (14): 1684-1695, 1997

33 Marcos S, "Aberrations and visual performance following standard laser vision correction" 17 (17): S596-S601, 2001