- Email: [email protected]
Correlation of higher order aberrations in the anterior corneal surface and degree of keratoconus measured with a Scheimpflug camera
ARTICLE IN PRESS a r c h s o c e s p o f t a l m o l . 2 0 1 6;x x x(x x):xxx–xxx
ARCHIVOS DE LA SOCIEDAD ESPAÑOLA DE OFTALMOLOGÍA www.elsevier.es/oftalmologia
Original article
Correlation of higher order aberrations in the anterior corneal surface and degree of keratoconus measured with a Scheimpflug camera夽,夽夽 S. Delgado a,∗ , J. Velazco a , R.M. Delgado Pelayo b , N. Ruiz-Quintero c a b c
Departamento de Córnea, Asociación para Evitar la Ceguera en México D.F., Coyoacán, Mexico Departamento de Córnea, Centro Cardio-Neuro-Oftlamológico y Trasplante, Santo Domingo, Dominican Republic Departamento de Córnea, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objective: To determine the correlation of higher order aberrations in anterior corneal sur-
Received 22 April 2015
face and degree of keratoconus measured with a Scheimpflug camera.
Accepted 4 January 2016
Material and methods: A descriptive, cross-sectional study was conducted on 152 eyes (both
Available online xxx
eyes of each patient) of patients with keratoconus, from January 2009 to April 2014. An
Keywords:
topographic mapping (by Amsler and Muckenhirn classification) was used to determine the
High order aberrations
degree of keratoconus. The correlation between high-order aberrations in anterior corneal
examination was performed on the corneal aberrometry in the anterior corneal surface, and
Scheimpflug
surface and the degree of keratoconus was determined.
Keratoconus
Results: Coma aberration significantly correlated with keratoconus severity (r = .60, p < 0.01),
Coma
as well as with the high order aberration (r = .61, p < 0.01). Trefoil and keratoconus were
Trefoil
weakly correlated (r = .34, p < 0.01). Conclusion: Higher order aberrations in anterior corneal surface were positively correlated with the degree of keratoconus in a similar way to the entire optical system. ˜ © 2016 Sociedad Espanola de Oftalmología. Published by Elsevier España, S.L.U. All rights reserved.
夽 Please cite this article as: Delgado S, Velazco J, Delgado Pelayo RM, Ruiz-Quintero N. Correlación de aberraciones de alto orden en la cara anterior de la córnea y el grado de queratocono medidas con cámara de Scheimpflug. Arch Soc Esp Oftalmol. 2016. http://dx.doi.org/ 10.1016/j.oftal.2016.01.014 夽夽 This work was presented at the National Congress of Ophthalmology Residents, Mexico City from 12 to 14 February and won first prize in the “Dr. Anselmo Fonte” award for free work in clinical sciences at the congress. 2015. ∗ Corresponding author. E-mail addresses: [email protected], sarai696 [email protected] (S. Delgado). ˜ 2173-5794/© 2016 Sociedad Espanola de Oftalmología. Published by Elsevier España, S.L.U. All rights reserved.
OFTALE-963; No. of Pages 4
ARTICLE IN PRESS 2
a r c h s o c e s p o f t a l m o l . 2 0 1 6;x x x(x x):xxx–xxx
Correlación de aberraciones de alto orden en la cara anterior de la córnea y el grado de queratocono medidas con cámara de Scheimpflug r e s u m e n Palabras clave:
Objetivo: Determinar la correlación de las aberraciones de alto orden en la cara anterior de
Aberraciones de alto orden
la córnea y el grado de queratocono medidas con cámara de Scheimpflug.
Scheimpflug
Material y métodos: Se realizó un estudio descriptivo y transversal en 152 ojos de pacientes
Queratocono
(ambos ojos de cada paciente) con queratocono, desde enero del 2009 hasta abril del 2014. Se
Coma
analizaron las aberraciones en la cara anterior de la córnea y se utilizó el mapa topográfico
Trefoil
(clasificación de Amsler y Muckenhirn) para determinar el grado de queratocono y encontrar la correlación que existe entre las aberraciones de alto orden en la cara anterior de la córnea y el grado de queratocono. Resultados: La aberración coma se correlacionó significativamente con la severidad del queratocono (r = 0.60; p < 0,01); de la misma forma que la aberraciones de alto orden (r = 0,61; p < 0,01). Trefoil y el grado de queratocono se correlacionaron en menor medida (r = 0,34; p < 0,01). Conclusiones: Las aberraciones de alto orden en la cara anterior de la córnea se correlacionan de forma positiva con el grado de queratocono, por lo que deberían ser consideradas en el abordaje diagnóstico de dicho padecimiento. ˜ de Oftalmología. Publicado por Elsevier España, S.L.U. Todos © 2016 Sociedad Espanola los derechos reservados.
Introduction Keratoconus is a bilateral non-inflammatory corneal ectasia which leads to protrusion, distortion and scarring of the cornea.1 The clinical signs are well defined, but early forms of the disease can go unnoticed unless a topographical study is performed.2 It is an uncommon condition; the annual incidence is estimated to be approximately one in every 2000 inhabitants. It affects all ethnic groups and has no gender predominance. In an assessment of corneal topography of first-degree relatives of patients with keratoconus, an incidence of 11% was found, compared with 0.05% in the general population.3,4 Although there are several hypotheses, the cause remains unknown. Most of the time it is an isolated condition.5 Some studies have identified hereditary factors as risk factors in keratoconus.6 It has also been associated with various syndromes such as Marfan’s and Down’s; between 0.5% and 15% as a possible result of rubbing the eyes, due to the high rate of blepharitis in this population. Other conditions such as atopy, use of contact lenses, eye trauma, connective tissue disorders and mitral valve prolapse have also been involved.7 Proinflammatory cytokine levels have been found to be elevated in keratoconus tears compared to a control group, indicating the development of chronic inflammatory events in the pathogenesis of the disease.8 Recent studies have evaluated the Shack–Hartmann wavefront sensor, which has proven its accuracy for obtaining the refraction value and measuring the eye aberrations without altering the accommodation state.9 In 2009, an article was published in the Revista Mexicana de Oftalmología [Mexican Journal of Ophthalmology] on a study of
55 eyes, which found that vertical coma is the predominant higher-order aberration in eyes with keratoconus and spherical aberration is a significant parameter for distinguishing between the different stages of keratoconus.10 It is now known that aberrations on the anterior surface of the cornea have greater involvement in patients with keratoconus.11 In patients with keratoconus, the anterior corneal surface is the most important source of optical errors. It is reported that in patients diagnosed with keratoconus, there is a greater presence of vertical coma aberrations.12–14 Aberrometry uses wavefront sensors to measure the complete refractive status, including irregular astigmatism in the optical system. In physical optics, light is expressed as a wave and light waves dissipate in all directions, like a spherical wave.15 The wavefront is the form of light waves in the input stage; light from infinity is perceived as a planar wavefront.5 Unlike the topographic analysis, wavefront technology can detect subclinical keratoconus with a sensitivity and specificity of 91% and 94% respectively.13 Other biomechanical factors of the cornea need to be considered.16 When beginning to interpret wavefront maps, the Optical Society of America (OSA, 2000) recommended the expansion of Zernike polynomials as the standard method for representing the error in the wavefront of an optical system. These are considered the basic description or building blocks of any wavefront. Corneal aberrometry can determine corneal optical aberrations, which constitute 80% of all total ocular aberrations.17 Higher-order aberrations (HOA) have been studied many times for refractive surgery. Maeda et al. applied wavefront technology to study aberrations in eyes with keratoconus.18 Wavefront technology is having an increasingly major impact on clinical practice: the correction of ocular aberrations
ARTICLE IN PRESS 3
a r c h s o c e s p o f t a l m o l . 2 0 1 6;x x x(x x):xxx–xxx
40 34 31
Women
30 23
%
Men 20 10
9 3
Women 46%
0
Men 54%
1
2
3
4
5
TKC
Fig. 2 – Keratoconus stage. Table 1 – Keratometry readings and average corneal thickness. Average (m)
Materials and methods We conducted a descriptive cross-sectional study in which higher-order aberrations on the anterior surface of the cornea were obtained using a Scheimpflug camera (Pentacam, Oculus Inc., Wetzlar, Germany) in patients diagnosed with keratoconus. Topographic mapping was also obtained to classify keratoconus stage. The study was conducted between January 2009 and April 2014. The procedures for obtaining data were consistent with the ethical standards of the responsible committee on human experimentation (institutional). Corneal aberrations were measured using the Scheimpflug camera, which has a programme that analyses the anterior corneal surface and measures the curvature and elevation, performs Fourier and Zernicke analyses, obtains 8 indices and classifies the morphology of the cornea and the possibility of keratoconus in 4 stages (adapted to Amsler and Muckenhirn), considering only the aberrations of the anterior corneal surface. Topographical and aberrometric maps were analysed for 152 eyes (both eyes of each patient) diagnosed with keratoconus and confirmed clinically and topographically, which had full records, topographical maps and reliable aberrometry. Patients with corneal lesions or scarring or with collagen diseases or previous eye surgery were excluded. All patients previously had a full eye examination. Lastly the coma, trefoil and higher-order aberrations were analysed and correlated with the degree of keratoconus.
Results We studied 152 eyes in 76 patients with keratoconus. The patient group consisted of 41 males (54%) and 35 females (46%) (Fig. 1). Out of the total, 52 eyes were keratoconus stage 3 (34%), 47 were stage 2 (31%), 35 stage 4 (23%), 13 stage 0 (9%) and 5 stage 1 (3%) (Fig. 2). The average keratometry for K1 was 50.37 ± 8.19 dioptres (36.2–76.4) and for K2 was
55.66 ± 8.54 dioptres (43.8–83.1). The average corneal thickness was 413.37 ± 100.41 micrometres (m) (Table 1). The average coma aberration was 4.33 ± 3.53 m and average trefoil aberration was 1.19 ± 1.42 m. There was a positive correlation between the degree of keratoconus and the coma aberration, with a value of 0.606 (Fig. 3); the correlation with the HOA was 0.611 (Fig. 4). Between trefoil and degree of keratoconus, it was 0.339 (Fig. 5). All the results had a p value of 0.01 and a 95% confidence interval.
30,000
Coma
opens up the possibility of an improvement in image optical quality in an individual. This is an objective and non-invasive test.19
50.37 ± 8.19 55.66 ± 8.54 413.37 ± 100.41
K1 K2 Corneal thickness
20,000
10,000
,000 0
1
2
3
4
TKC
Fig. 3 – Correlation between the coma aberration and keratoconus stage. 15,000
RMS HOA
Fig. 1 – Gender of the patients diagnosed with keratoconus.
10,000
5,000
,000 0
1
2
3
4
TKC
Fig. 4 – Correlation between the keratoconus stage and the RMS of the higher-order aberrations. RMS: root mean square.
ARTICLE IN PRESS 4
a r c h s o c e s p o f t a l m o l . 2 0 1 6;x x x(x x):xxx–xxx
references
10,000
Trefoil
8,000 6,000 4,000 2,000 ,000
0
1
2
3
4
TKC
Fig. 5 – Correlation between the trefoil aberration and keratoconus stage.
Discussion The majority of the patients were male, in line with findings reported in the literature. The correlation was higher in the higher-order aberration and coma; it proved to be lower in trefoil. In this study, we found that coma and HOA on the anterior corneal surface increase as the degree of keratoconus increases. This had been reported previously for the aberrations taken from the optical system as a whole. From that, we established that this correlation could be mainly due to the corneal aberrations on the anterior surface, and not the total ocular aberrations. Our findings that the main HOA in eyes with keratoconus is the coma are consistent with the Maeda y Alió studies. The Alió and Shabayek study reports that the coma-type aberration could be used as a guide to distinguish between the different keratoconus stages, as they found a statistically significant correlation between the coma aberration and the average keratometry.18 The clinical relevance of the study is obtaining objective and non-invasive information using wavefront technology in the study of keratoconus and HOA. Most of the published studies focused on studying total aberrations in eyes with keratoconus. However, we propose that the aberrations on the anterior surface of the cornea are representative of the entire optical system and significantly correlated with the degree of keratoconus. Nonetheless, we would advocate conducting further studies to support the data obtained in this analysis. In conclusion, the study of HOA on the anterior surface of the cornea in eyes with keratoconus could be a diagnostic tool for staging and quantifying the degree of keratoconus when this condition is suspected and these HOA should therefore be considered in future classifications.
Ethics This protocol was designed based on ethical principles for medical research involving human beings adopted by the 18th World Medical Assembly in Helsinki.
Conflicts of interest No conflicts of interest declared.
1. Masters BR. David Maurice’s contribution to ophthalmic instrumentation: roots of the scanning slit confocal microscope. Exp Eye Res. 2004;78:315–26. 2. Bayhan HA. Repeatability of aberrometric measurements in normal and keratoconus eyes using a new Scheimpflug-Placido topographer. J Cataract Refract Surg. 2014;40:269–75. 3. Laing RA, Oak, Leibowitz HM. Specialized microscopy of the cornea. In: Leibowitz HM, Waring GO, editors. Corneal disorders. Philadelphia: W.B. Saunders; 1998. p. 83–122. 4. Koester CJ. Scanning mirror microscope with optical sectioning characteristics: applications in ophthalmology. Appl Opt. 1980;19:1749–57. 5. Maeda N. Clinical applications of wave front aberrometry – a review. Clin Exp Ophthalmol. 2009;37:118–29. 6. Wang GY, Rabinowitz YS, Rotter JI, Yang H. Genetic epidemiological study of keratoconus: evidence for major gene determination. Am J Med Genet. 2000;93: 403–9. 7. Romero-J, Santodomingo R. Keratoconus: a review contact lens and anterior eye. J Br Contact Lens Assoc. 2010;33: 157–66. 8. Lema I, Sobrino T. Subclinical keratoconus and inflammatory molecules from tears. Br J Ophthalmol. 2009;93: 820–4. 9. Ochoa-Tabares JC, Hernández-Quintela E, Ruiz-Quintero N, Naranjo-Tackman R. Accuracy of a Hartmann Shack aberrometer system to assess the ocular aberrations. Rev Mex Oftalmol. 2012;86:25–32. 10. Torres-Soriano KE, Ruiz-Quintero N, Naranjo-Tackman R. Aberraciones de alto orden en ojos con queratocono, medidas mediante análisis de frente de onda Hartmann–Shack. Rev Mex Oftalmol. 2009;83:100–5. 11. Bühren J, Daniel Kook. Detection of subclinical keratoconus by using corneal anterior and posterior surface aberrations and thickness spatial profiles. Invest Ophthalmol Vis Sci. 2010;51:3424–32. 12. Barbero S, Marcos S, Merayo-Lloves J, Moreno-Barriuso E. Validation of the estimation of corneal aberrations from videokeratography in keratoconus. J Refract Surg. 2002;18:263–70. 13. Buhren J, Kuhne C, Kohnen T. Defining subclinical keratoconus using corneal first-surface higher-order aberrations. Am J Ophthalmol. 2007;143:381–9. 14. Gobbe M, Guillon M. Corneal wavefront aberration measurements to detect keratoconus patients. Cont Lens Anterior Eye. 2005;28:57–66. 15. Goebels S, Eppig T. Detection of early forms of keratoconus: current screening methods. Klin Monbl Augenheilkd. 2013;230:998–1004. ˜ 16. Alió JL, Pinero DP, Alesón A, Teus MA, Barraquer RI, Murta J, et al. Keratoconus-integrated characterization considering anterior corneal aberrations, internal astigmatism, and corneal biomechanics. J Cataract Refract Surg. 2011;37: 552–68. 17. Smolek MK. Method for expressing clinical and statistical significance of ocular and corneal wave front error aberrations. Cornea. 2012;31:212–21. 18. Alió J. Corneal higher order aberrations. J Refract Surg. 2006;22:539–45. 19. Maeda N. Wavefront aberrations measured with Hartmann-Shack sensor in patients with keratoconus. Ophthalmology. 2002;11:1996–2003.
ARCHIVOS DE LA SOCIEDAD ESPAÑOLA DE OFTALMOLOGÍA www.elsevier.es/oftalmologia
Original article
Correlation of higher order aberrations in the anterior corneal surface and degree of keratoconus measured with a Scheimpflug camera夽,夽夽 S. Delgado a,∗ , J. Velazco a , R.M. Delgado Pelayo b , N. Ruiz-Quintero c a b c
Departamento de Córnea, Asociación para Evitar la Ceguera en México D.F., Coyoacán, Mexico Departamento de Córnea, Centro Cardio-Neuro-Oftlamológico y Trasplante, Santo Domingo, Dominican Republic Departamento de Córnea, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objective: To determine the correlation of higher order aberrations in anterior corneal sur-
Received 22 April 2015
face and degree of keratoconus measured with a Scheimpflug camera.
Accepted 4 January 2016
Material and methods: A descriptive, cross-sectional study was conducted on 152 eyes (both
Available online xxx
eyes of each patient) of patients with keratoconus, from January 2009 to April 2014. An
Keywords:
topographic mapping (by Amsler and Muckenhirn classification) was used to determine the
High order aberrations
degree of keratoconus. The correlation between high-order aberrations in anterior corneal
examination was performed on the corneal aberrometry in the anterior corneal surface, and
Scheimpflug
surface and the degree of keratoconus was determined.
Keratoconus
Results: Coma aberration significantly correlated with keratoconus severity (r = .60, p < 0.01),
Coma
as well as with the high order aberration (r = .61, p < 0.01). Trefoil and keratoconus were
Trefoil
weakly correlated (r = .34, p < 0.01). Conclusion: Higher order aberrations in anterior corneal surface were positively correlated with the degree of keratoconus in a similar way to the entire optical system. ˜ © 2016 Sociedad Espanola de Oftalmología. Published by Elsevier España, S.L.U. All rights reserved.
夽 Please cite this article as: Delgado S, Velazco J, Delgado Pelayo RM, Ruiz-Quintero N. Correlación de aberraciones de alto orden en la cara anterior de la córnea y el grado de queratocono medidas con cámara de Scheimpflug. Arch Soc Esp Oftalmol. 2016. http://dx.doi.org/ 10.1016/j.oftal.2016.01.014 夽夽 This work was presented at the National Congress of Ophthalmology Residents, Mexico City from 12 to 14 February and won first prize in the “Dr. Anselmo Fonte” award for free work in clinical sciences at the congress. 2015. ∗ Corresponding author. E-mail addresses: [email protected], sarai696 [email protected] (S. Delgado). ˜ 2173-5794/© 2016 Sociedad Espanola de Oftalmología. Published by Elsevier España, S.L.U. All rights reserved.
OFTALE-963; No. of Pages 4
ARTICLE IN PRESS 2
a r c h s o c e s p o f t a l m o l . 2 0 1 6;x x x(x x):xxx–xxx
Correlación de aberraciones de alto orden en la cara anterior de la córnea y el grado de queratocono medidas con cámara de Scheimpflug r e s u m e n Palabras clave:
Objetivo: Determinar la correlación de las aberraciones de alto orden en la cara anterior de
Aberraciones de alto orden
la córnea y el grado de queratocono medidas con cámara de Scheimpflug.
Scheimpflug
Material y métodos: Se realizó un estudio descriptivo y transversal en 152 ojos de pacientes
Queratocono
(ambos ojos de cada paciente) con queratocono, desde enero del 2009 hasta abril del 2014. Se
Coma
analizaron las aberraciones en la cara anterior de la córnea y se utilizó el mapa topográfico
Trefoil
(clasificación de Amsler y Muckenhirn) para determinar el grado de queratocono y encontrar la correlación que existe entre las aberraciones de alto orden en la cara anterior de la córnea y el grado de queratocono. Resultados: La aberración coma se correlacionó significativamente con la severidad del queratocono (r = 0.60; p < 0,01); de la misma forma que la aberraciones de alto orden (r = 0,61; p < 0,01). Trefoil y el grado de queratocono se correlacionaron en menor medida (r = 0,34; p < 0,01). Conclusiones: Las aberraciones de alto orden en la cara anterior de la córnea se correlacionan de forma positiva con el grado de queratocono, por lo que deberían ser consideradas en el abordaje diagnóstico de dicho padecimiento. ˜ de Oftalmología. Publicado por Elsevier España, S.L.U. Todos © 2016 Sociedad Espanola los derechos reservados.
Introduction Keratoconus is a bilateral non-inflammatory corneal ectasia which leads to protrusion, distortion and scarring of the cornea.1 The clinical signs are well defined, but early forms of the disease can go unnoticed unless a topographical study is performed.2 It is an uncommon condition; the annual incidence is estimated to be approximately one in every 2000 inhabitants. It affects all ethnic groups and has no gender predominance. In an assessment of corneal topography of first-degree relatives of patients with keratoconus, an incidence of 11% was found, compared with 0.05% in the general population.3,4 Although there are several hypotheses, the cause remains unknown. Most of the time it is an isolated condition.5 Some studies have identified hereditary factors as risk factors in keratoconus.6 It has also been associated with various syndromes such as Marfan’s and Down’s; between 0.5% and 15% as a possible result of rubbing the eyes, due to the high rate of blepharitis in this population. Other conditions such as atopy, use of contact lenses, eye trauma, connective tissue disorders and mitral valve prolapse have also been involved.7 Proinflammatory cytokine levels have been found to be elevated in keratoconus tears compared to a control group, indicating the development of chronic inflammatory events in the pathogenesis of the disease.8 Recent studies have evaluated the Shack–Hartmann wavefront sensor, which has proven its accuracy for obtaining the refraction value and measuring the eye aberrations without altering the accommodation state.9 In 2009, an article was published in the Revista Mexicana de Oftalmología [Mexican Journal of Ophthalmology] on a study of
55 eyes, which found that vertical coma is the predominant higher-order aberration in eyes with keratoconus and spherical aberration is a significant parameter for distinguishing between the different stages of keratoconus.10 It is now known that aberrations on the anterior surface of the cornea have greater involvement in patients with keratoconus.11 In patients with keratoconus, the anterior corneal surface is the most important source of optical errors. It is reported that in patients diagnosed with keratoconus, there is a greater presence of vertical coma aberrations.12–14 Aberrometry uses wavefront sensors to measure the complete refractive status, including irregular astigmatism in the optical system. In physical optics, light is expressed as a wave and light waves dissipate in all directions, like a spherical wave.15 The wavefront is the form of light waves in the input stage; light from infinity is perceived as a planar wavefront.5 Unlike the topographic analysis, wavefront technology can detect subclinical keratoconus with a sensitivity and specificity of 91% and 94% respectively.13 Other biomechanical factors of the cornea need to be considered.16 When beginning to interpret wavefront maps, the Optical Society of America (OSA, 2000) recommended the expansion of Zernike polynomials as the standard method for representing the error in the wavefront of an optical system. These are considered the basic description or building blocks of any wavefront. Corneal aberrometry can determine corneal optical aberrations, which constitute 80% of all total ocular aberrations.17 Higher-order aberrations (HOA) have been studied many times for refractive surgery. Maeda et al. applied wavefront technology to study aberrations in eyes with keratoconus.18 Wavefront technology is having an increasingly major impact on clinical practice: the correction of ocular aberrations
ARTICLE IN PRESS 3
a r c h s o c e s p o f t a l m o l . 2 0 1 6;x x x(x x):xxx–xxx
40 34 31
Women
30 23
%
Men 20 10
9 3
Women 46%
0
Men 54%
1
2
3
4
5
TKC
Fig. 2 – Keratoconus stage. Table 1 – Keratometry readings and average corneal thickness. Average (m)
Materials and methods We conducted a descriptive cross-sectional study in which higher-order aberrations on the anterior surface of the cornea were obtained using a Scheimpflug camera (Pentacam, Oculus Inc., Wetzlar, Germany) in patients diagnosed with keratoconus. Topographic mapping was also obtained to classify keratoconus stage. The study was conducted between January 2009 and April 2014. The procedures for obtaining data were consistent with the ethical standards of the responsible committee on human experimentation (institutional). Corneal aberrations were measured using the Scheimpflug camera, which has a programme that analyses the anterior corneal surface and measures the curvature and elevation, performs Fourier and Zernicke analyses, obtains 8 indices and classifies the morphology of the cornea and the possibility of keratoconus in 4 stages (adapted to Amsler and Muckenhirn), considering only the aberrations of the anterior corneal surface. Topographical and aberrometric maps were analysed for 152 eyes (both eyes of each patient) diagnosed with keratoconus and confirmed clinically and topographically, which had full records, topographical maps and reliable aberrometry. Patients with corneal lesions or scarring or with collagen diseases or previous eye surgery were excluded. All patients previously had a full eye examination. Lastly the coma, trefoil and higher-order aberrations were analysed and correlated with the degree of keratoconus.
Results We studied 152 eyes in 76 patients with keratoconus. The patient group consisted of 41 males (54%) and 35 females (46%) (Fig. 1). Out of the total, 52 eyes were keratoconus stage 3 (34%), 47 were stage 2 (31%), 35 stage 4 (23%), 13 stage 0 (9%) and 5 stage 1 (3%) (Fig. 2). The average keratometry for K1 was 50.37 ± 8.19 dioptres (36.2–76.4) and for K2 was
55.66 ± 8.54 dioptres (43.8–83.1). The average corneal thickness was 413.37 ± 100.41 micrometres (m) (Table 1). The average coma aberration was 4.33 ± 3.53 m and average trefoil aberration was 1.19 ± 1.42 m. There was a positive correlation between the degree of keratoconus and the coma aberration, with a value of 0.606 (Fig. 3); the correlation with the HOA was 0.611 (Fig. 4). Between trefoil and degree of keratoconus, it was 0.339 (Fig. 5). All the results had a p value of 0.01 and a 95% confidence interval.
30,000
Coma
opens up the possibility of an improvement in image optical quality in an individual. This is an objective and non-invasive test.19
50.37 ± 8.19 55.66 ± 8.54 413.37 ± 100.41
K1 K2 Corneal thickness
20,000
10,000
,000 0
1
2
3
4
TKC
Fig. 3 – Correlation between the coma aberration and keratoconus stage. 15,000
RMS HOA
Fig. 1 – Gender of the patients diagnosed with keratoconus.
10,000
5,000
,000 0
1
2
3
4
TKC
Fig. 4 – Correlation between the keratoconus stage and the RMS of the higher-order aberrations. RMS: root mean square.
ARTICLE IN PRESS 4
a r c h s o c e s p o f t a l m o l . 2 0 1 6;x x x(x x):xxx–xxx
references
10,000
Trefoil
8,000 6,000 4,000 2,000 ,000
0
1
2
3
4
TKC
Fig. 5 – Correlation between the trefoil aberration and keratoconus stage.
Discussion The majority of the patients were male, in line with findings reported in the literature. The correlation was higher in the higher-order aberration and coma; it proved to be lower in trefoil. In this study, we found that coma and HOA on the anterior corneal surface increase as the degree of keratoconus increases. This had been reported previously for the aberrations taken from the optical system as a whole. From that, we established that this correlation could be mainly due to the corneal aberrations on the anterior surface, and not the total ocular aberrations. Our findings that the main HOA in eyes with keratoconus is the coma are consistent with the Maeda y Alió studies. The Alió and Shabayek study reports that the coma-type aberration could be used as a guide to distinguish between the different keratoconus stages, as they found a statistically significant correlation between the coma aberration and the average keratometry.18 The clinical relevance of the study is obtaining objective and non-invasive information using wavefront technology in the study of keratoconus and HOA. Most of the published studies focused on studying total aberrations in eyes with keratoconus. However, we propose that the aberrations on the anterior surface of the cornea are representative of the entire optical system and significantly correlated with the degree of keratoconus. Nonetheless, we would advocate conducting further studies to support the data obtained in this analysis. In conclusion, the study of HOA on the anterior surface of the cornea in eyes with keratoconus could be a diagnostic tool for staging and quantifying the degree of keratoconus when this condition is suspected and these HOA should therefore be considered in future classifications.
Ethics This protocol was designed based on ethical principles for medical research involving human beings adopted by the 18th World Medical Assembly in Helsinki.
Conflicts of interest No conflicts of interest declared.
1. Masters BR. David Maurice’s contribution to ophthalmic instrumentation: roots of the scanning slit confocal microscope. Exp Eye Res. 2004;78:315–26. 2. Bayhan HA. Repeatability of aberrometric measurements in normal and keratoconus eyes using a new Scheimpflug-Placido topographer. J Cataract Refract Surg. 2014;40:269–75. 3. Laing RA, Oak, Leibowitz HM. Specialized microscopy of the cornea. In: Leibowitz HM, Waring GO, editors. Corneal disorders. Philadelphia: W.B. Saunders; 1998. p. 83–122. 4. Koester CJ. Scanning mirror microscope with optical sectioning characteristics: applications in ophthalmology. Appl Opt. 1980;19:1749–57. 5. Maeda N. Clinical applications of wave front aberrometry – a review. Clin Exp Ophthalmol. 2009;37:118–29. 6. Wang GY, Rabinowitz YS, Rotter JI, Yang H. Genetic epidemiological study of keratoconus: evidence for major gene determination. Am J Med Genet. 2000;93: 403–9. 7. Romero-J, Santodomingo R. Keratoconus: a review contact lens and anterior eye. J Br Contact Lens Assoc. 2010;33: 157–66. 8. Lema I, Sobrino T. Subclinical keratoconus and inflammatory molecules from tears. Br J Ophthalmol. 2009;93: 820–4. 9. Ochoa-Tabares JC, Hernández-Quintela E, Ruiz-Quintero N, Naranjo-Tackman R. Accuracy of a Hartmann Shack aberrometer system to assess the ocular aberrations. Rev Mex Oftalmol. 2012;86:25–32. 10. Torres-Soriano KE, Ruiz-Quintero N, Naranjo-Tackman R. Aberraciones de alto orden en ojos con queratocono, medidas mediante análisis de frente de onda Hartmann–Shack. Rev Mex Oftalmol. 2009;83:100–5. 11. Bühren J, Daniel Kook. Detection of subclinical keratoconus by using corneal anterior and posterior surface aberrations and thickness spatial profiles. Invest Ophthalmol Vis Sci. 2010;51:3424–32. 12. Barbero S, Marcos S, Merayo-Lloves J, Moreno-Barriuso E. Validation of the estimation of corneal aberrations from videokeratography in keratoconus. J Refract Surg. 2002;18:263–70. 13. Buhren J, Kuhne C, Kohnen T. Defining subclinical keratoconus using corneal first-surface higher-order aberrations. Am J Ophthalmol. 2007;143:381–9. 14. Gobbe M, Guillon M. Corneal wavefront aberration measurements to detect keratoconus patients. Cont Lens Anterior Eye. 2005;28:57–66. 15. Goebels S, Eppig T. Detection of early forms of keratoconus: current screening methods. Klin Monbl Augenheilkd. 2013;230:998–1004. ˜ 16. Alió JL, Pinero DP, Alesón A, Teus MA, Barraquer RI, Murta J, et al. Keratoconus-integrated characterization considering anterior corneal aberrations, internal astigmatism, and corneal biomechanics. J Cataract Refract Surg. 2011;37: 552–68. 17. Smolek MK. Method for expressing clinical and statistical significance of ocular and corneal wave front error aberrations. Cornea. 2012;31:212–21. 18. Alió J. Corneal higher order aberrations. J Refract Surg. 2006;22:539–45. 19. Maeda N. Wavefront aberrations measured with Hartmann-Shack sensor in patients with keratoconus. Ophthalmology. 2002;11:1996–2003.