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2018, Cilt 57, Sayı 1, Sayfa(lar) 019-025
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Comparison of anterior segment parameters between pediatric and adult keratoconus groups
İbrahim Toprak1, Cem Yıldırım2, Volkan Yaylalı2
1Servergazi State Hospital, Clinic of Ophthalmology, Denizli, Turkey
2Pamukkale University Faculty of Medicine, Department of Ophthalmology, Denizli, Turkey
Keywords: Age, anterior segment, keratoconus, pediatrics, scheimpflug
Abstract
Aim: To determine differences in anterior segment measurements between pediatric and adult keratoconus groups using Scheimpflug imaging system.

Materials and Methods: This retrospective study included 133 patients with keratoconus and 101 healthy controls. Subjects were grouped as pediatric and adult. Differences in anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA), pachymetry, corneal volume (CV) and maximum keratometry (Kmax) were sought between the age-based subgroups.

Results: Right eyes of the 133 keratoconus patients (56 pediatrics and 77 adults) and 101 healthy controls (41 pediatrics and 60 adults) were reviewed. Pediatric subgroups had significantly higher ACD and ACV compared to those of the adult subgroups in both groups (p<0.05). On the other hand, pediatric and adult keratoconus patients had significantly higher ACD than in the age (subgroup) matched controls (p< 0.05). In the pediatric keratoconus subgroup, eyes with stage 3 keratoconus had significantly deeper ACD than in the eyes with stage 2 keratoconus (p<0.05). However, in the adult group, only corneal parameters were significantly lower in eyes with stage 3 keratoconus compared to those of the eyes with stage 2 keratoconus (p<0.05).

Conclusion: Anterior chamber measurements appear to be altered by aging in both keratoconus and control groups, whereas eyes with keratoconus in all age subgroups appear to have a deeper AC than in the age-matched normals. Moreover, an increase in ACD in pediatric keratoconus might be indicative of progression. However, in the adult keratoconus, corneal parameters appear to decrease with keratoconus progression.

  • Top
  • Abstract
  • Introduction
  • Methods
  • Results
  • Disscussion
  • Conclusion
  • References
  • Introduction
    Keratoconus is a non-inflammatory progressive corneal disease characterized by apical protrusion and stromal thinning 1. Environmental and genetic factors play role in the pathogenesis and the disease begins at puberty 1. However, clinical manifestation of keratoconus takes time and diagnosis is generally established in early adulthood. Most of the early cases are detected during the preoperative examinations prior to the refractive surgery over 18 years of age. It is well known that pediatric keratoconus has tendency to progress rapidly and corneal transplantation is generally required in 20% of the patients 1-3. Fortunately, corneal collagen cross-linking (CXL) treatment provides promising visual and topographical improvement in patients with progressive keratoconus 2-5.

    Visual deterioration in pediatric age group should be carefully evaluated and a comprehensive ophthalmological examination is needed. Keratoconus should be kept in mind as an important etiology in pediatric patients with myopia and astigmatism. In moderate to advanced keratoconus, typical clinical signs such as stromal thinning, Fleischer's ring, Munson's sign, Rizzuti's phenomenon and scissoring reflex on dilated retinoscopy help for the accurate diagnosis. However, in early keratoconus, new technology anterior segment imaging devices provide valuable anterior segment data for the diagnosis 6-8.

    The Scheimpflug imaging system has ability of taking high quality slit images of the anterior segment structures from anterior surface of the cornea to the posterior of the lens using a 3600 rotating camera. This technology provides quantitative data for anterior chamber and lens, corneal curvature, anterior and posterior elevation, corneal pachymetry and corneal volume 6-8.

    In the current literature, there are studies comparing Scheimpflug parameters between eyes with keratoconus and healthy controls in adult population, whereas there is limited data regarding anterior segment features of eyes with keratoconus in pediatric age group 9,10. In the current study, we performed an age-based comparison (as pediatrics and adults) in terms of anterior segment measurements obtained from the Scheimpflug imaging system (anterior chamber parameters, corneal thicknesses, corneal volume and maximum keratometry [Kmax]) between patients with keratoconus and healthy subjects.

  • Top
  • Abstract
  • Introduction
  • Methods
  • Results
  • Disscussion
  • Conclusion
  • References
  • Methods
    This study followed the tenets of the Declaration of Helsinki and Local Ethics Committee approved the methodology. We retrospectively reviewed the records of 133 right eyes of 133 patients with a confirmed diagnosis of keratoconus (keratoconus group) and 101 right eyes of 101 healthy controls (control group) aged between 10-40 years. Both keratoconus and control groups were divided into two age subgroups as pediatric (age< 18 years) and adult (age≥ 18 years). In the keratoconus group, age subgroups were matched with each other in terms of gender and keratoconus stage.

    Inclusion criteria for the keratoconus group were biomicroscopic examination and corneal topography consistent with keratoconus according to the criteria of Collaborative Longitudinal Evaluation of Keratoconus Study Group, 11 inferior–superior (I-S) keratometric asymmetry >1.5, skewing of the steepest radial axes above and below the horizontal meridian, stromal thinning, Fleischer's ring, Munson's sign, Rizzuti's phenomenon and scissoring reflex on dilated retinoscopy.

    The control group consisted of age- and gender- matched healthy subjects with normal ophthalmological examination and corneal topography (except regular astigmatism, if any).

    Eyes with subclinical or form fruste keratoconus, history of prior corneal surgery, trauma or scarring were excluded from the study.

    In the keratoconus group, disease severity was graded according to the Amsler-Krumeich Classification System 12 as follows;

    Stage 1: Eccentric steepening; myopia, induced astigmatism, or both <5.00 D; mean central K < 48 D

    Stage 2: Myopia, induced astigmatism, or both from 5.00 to 8.00 D; mean central K readings < 53.00 D; absence of scarring; corneal thickness >400 microns

    Stage 3: Myopia, induced astigmatism, or both from 8.00 to 10.00 D; mean central K readings >53.00 D, absence of scarring; corneal thickness 300 – 400 microns

    Stage 4: Refraction not measurable; mean central K readings >55.00 D; central corneal scarring, corneal thickness < 200 microns

    All patients underwent detailed ophthalmological examinations included best corrected distance visual acuity (CDVA, including contact lens) measurement with Snellen charts, slit-lamp biomicroscopic examination, applanation tonometry, dilated fundus examination (with +90 D lens) and retinoscopy. Eyes with stage 4 keratoconus were not included into the study to prevent potential effect of corneal scarring on the Scheimpflug measurements.

    Scheimpflug imaging
    A single experienced technician performed the anterior segment measurements using the Oculus Pentacam (Oculus Optikgerate GmbH, Wetzlar, Germany). Images were captured in automatic mode under scotopic conditions with undilated pupils. A single test with the highest quality score (over 95%) was used for the statistical analysis.

    Anterior chamber depth (ACD, distance from the corneal endothelium to the anterior lens surface with undilated pupil along the optical axis), anterior chamber volume (ACV, calculated from the corneal endothelium to the anterior lens surface with undilated pupil in a 12 mm diameter around the corneal apex), anterior chamber angle (ACA), pupil-center pachymetry, apical pachymetry, thinnest pachymetry, corneal volume (CV) and Kmax were obtained for each eye.

    The differences in Scheimpflug measurements between pediatric and adult subgroups were investigated within the keratoconus and control groups separately. Pediatric vs. pediatric and adult vs. adult comparisons were also performed regarding the Scheimpflug parameters between the keratoconus and control groups. Moreover, in each keratoconus subgroup (pediatric and adult), we sought for differences in the Scheimpflug measurements based on the keratoconus stage.

    Statistical analysis
    The sample size in this study was calculated using the PASS software version 11.0.1 (NSCC, LLC, Utah, USA). Statistical analysis was performed with the Statistical Package for Social Sciences software version 16.0 (SPSS Inc, Chicago, IL, USA). Results were expressed as mean ± standard deviation (SD). The differences in gender and keratoconus stage between the two age subgroups were analyzed using the Chi Square test. An independent samples t test was used to analyze the differences regarding quantitative variables (Scheimpflug system measurements) between the pediatric and adult subgroups in the keratoconus and control groups.

    However, a Mann-Whitney U test (nonparametric) or an independent samples t test (parametric) was performed to compare two independent subgroups [Pediatric vs. pediatric and adult vs. adult comparisons (keratoconus vs. control groups), and comparisons between eyes with stage 2 and 3 keratoconus] in terms of quantitative variables (Scheimpflug parameters).

    Pearson correlation coefficients were used to analyze relations between age and Scheimpflug parameters. A p value less than 0.05 was considered statistically significant at 95 % confidence interval.

  • Top
  • Abstract
  • Introduction
  • Methods
  • Results
  • Disscussion
  • Conclusion
  • References
  • Results
    This study involved 133 patients with confirmed keratoconus (keratoconus group, 56 pediatrics and 77 adults) and 101 age-and gender-matched healthy controls (control group, 41 pediatrics and 60 adults). Table-1 presents age, gender distribution and Scheimpflug measurements between the keratoconus and control groups. The keratoconus group consisted of only eyes with stage 2 (n=61) and stage 3 (n=72) keratoconus.


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    Table 1: Age, Gender Distribution and Scheimpflug Measurements Between The Keratoconus and Control Groups.

    In the keratoconus group, age-based analysis showed that the pediatric subgroup had significantly higher ACD and ACV values when compared to those of the adult subgroup (Table-2, p<0.001, p=0.011, respectively). Similarly, in the control group, ACD and ACV values were significantly higher in the pediatric subgroup than in the adults (Table-2, p=0.002, p<0.001, respectively). Table-2 shows comparisons for the Scheimpflug parameters within the keratoconus and control groups based on the age subgroups.


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    Table 2: Comparison of the Scheimpflug Measurements Based on Age Subgroups Within the Keratoconus and Control Groups.

    Furthermore, pediatric patients with keratoconus had higher ACD than in the healthy pediatrics (3.60±0.33 vs. 3.43±0.36 mm, respectively, p=0.020). Similarly, adult patients with keratoconus had higher ACD (3.39±0.30 vs. 3.22±0.28 mm, respectively, p=0.001), and lower ACA (37.9±6.2 vs. 40.1±5.2 degrees, respectively, p=0.031) values than in the healthy adults.

    As expected, all keratoconus subgroups had significantly higher Kmax, and lower corneal pachymetry and corneal volume compared to those of the healthy age-based subgroups (p<0.001).

    In the keratoconus group, there were no statistically significant differences in terms of gender, keratoconus severity (based on the Amsler-Krumeich Classification System), corneal thicknesses, corneal volume and Kmax between the pediatric and adult subgroups (p>0.05).

    The Scheimpflug measurements were also compared according to the keratoconus stage within the each age-based subgroup (pediatric and adult). In the pediatric subgroup, ACD was significantly higher in eyes with stage 3 keratoconus (n=30) than in the eyes with stage 2 keratoconus (n=26) (p=0.045). In the adult subgroup, AC parameters did not change between the eyes with stage 2 (n=35) and stage 3 (n=42) keratoconus, whereas eyes with stage 3 keratoconus had lower corneal thicknesses (p<0.001) and CV (p=0.006) than in the eyes with stage 2 keratoconus. Figure 1, Figure 2 and Figure 3 present the comparisons of the Scheimpflug AC parameters based on the keratoconus stage in each age subgroup.


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    Figure 1: Comparison of anterior chamber depth (ACD) between eyes with stage 2 and stage 3 keratoconus in the pediatric and adult keratoconus subgroups (*statistically significant difference, p<0.05).


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    Figure 2: Comparison of anterior chamber volume (ACV) between eyes with stage 2 and stage 3 keratoconus in the pediatric and adult keratoconus subgroups (p>0.05).


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    Figure 3: Comparison of anterior chamber angle (ACA) between eyes with stage 2 and stage 3 keratoconus in the pediatric and adult keratoconus subgroups (p>0.05).

    In the keratoconus group, correlation analysis revealed a significant negative relation between age and AC parameters (ACD, p<0.001 r=-0.349; ACV, p=0.001 r=0.295). In the control group, ACD and ACV were negatively correlated with age (p= 0.001, r=-0.317; p<0.001, r=-0.346, respectively). However, in both groups, age was not significantly correlated with corneal thicknesses, CV and Kmax (p>0.05).

  • Top
  • Abstract
  • Introduction
  • Methods
  • Results
  • Disscussion
  • Conclusion
  • References
  • Discussion
    Keratoconus is a bilateral and asymmetric corneal disease. Although underlying mechanisms begin at puberty, the disease generally manifests at early adulthood and typical findings make the diagnosis easy 1-3. However, a complete anterior segment imaging is crucial for establishing the diagnosis. A relatively new anterior segment imaging device, the Scheimpflug system, provides reliable and reproducible quantitative data for anterior segment structures 13-16.

    In the current literature, several researchers evaluated anterior chamber parameters of eyes with keratoconus using the Scheimpflug system and it was suggested that keratoconic eyes had a higher ACD compared to that of the healthy eyes 17-19. A further analysis by Emre et al. 9 showed statistically significant differences in ACA and CV measurements between the mild and severe keratoconus groups and ACV was higher in the severe keratoconus group than in the control group. In terms of corneal parameters, previous studies reported reduced corneal volume and corneal thickness in eyes with keratoconus compared to those of the healthy controls 17-19.

    Although above-mentioned studies investigated differences in anterior chamber measurements, CV and pachymetry in adult keratoconus, current literature has limited data comparing anterior segment parameters between the pediatric and adult patients with keratoconus. In the present study, we sought for differences in ACD, ACV, ACA, corneal pachymetry, CV and Kmax obtained from the Scheimpflug imaging system between pediatrics and adults within/between the keratoconus and control groups. Statistical analysis revealed that, in both keratoconus and control groups, pediatric subjects (<18 years of age) had a deeper AC and larger ACV when compared to those of the adults (≥ 18 years of age). This result might be associated with the role of aging on AC shallowing as stated by previous studies 10,20.

    It was suggested that age, gender, refractive error, body type and cataract formation are related with ACD measurement 10,20. A study by Edmonds et al. 10 showed that ACD was decreased by an average of 0.012 mm/year in a normal eye and by 0.014 mm in eyes with keratoconus. Similarly, in the current study, correlation analysis revealed a negative relation between age and AC measurements in the keratoconus and control groups. Moreover, the results of our study demonstrated a similar decrease in ACD and ACV values between the pediatric and adult groups in patients with keratoconus and healthy subjects. Hence, it can be suggested that shallowing of AC in the pediatric keratoconus subgroup over time was due to physiological process as in normal population. On the other hand, we did not have lens thickness measurements (which could be a valuable parameter) for all subjects so this parameter was not included into the statistical comparisons. This point can be considered as a limitation of the present study. Although both keratoconus patients and healthy subjects seem to show similar trend in AC measurements with aging, our study showed that pediatrics and adults with keratoconus had deeper AC than in the age-matched corresponding healthy subgroups.

    In our study, corneal thicknesses, CV and Kmax showed no significant differences between the pediatric and adult keratoconus subgroups. In the current study, age subgroups were matched with each other in terms of gender and keratoconus severity. Therefore, we were able to perform a reliable analysis to evaluate the effect of age on differences in anterior segment parameters between the keratoconus subgroups, whereas this condition might have led similar Kmax values between the subgroups.

    In the current literature, there are few number of studies comparing Scheimpflug parameters between pediatric and adult patients with keratoconus, whereas Emre et al. 9 evaluated the Scheimpflug anterior segment parameters with a severity-based comparison in keratoconus patients, and their study group included patients with an age between 12 to 63 years. In our study, we performed a similar comparison in terms of Scheimpflug parameters between the eyes with stage 2 and stage 3 keratoconus in the pediatric and adult keratoconus subgroups separately (our study group consisted of only eyes with stage 2 and 3 keratoconus). In the pediatric subgroup, ACD was significantly higher in eyes with more severe keratoconus, whereas there were no significant differences in AC parameters between the stage 2 and stage 3 keratoconus in the adult subgroup. When corneal parameters were evaluated, in the pediatric subgroup, there were no differences in terms of corneal thicknesses and volume between the stage 2 and stage 3 keratoconus, whereas in the adult subgroup, eyes with stage 3 keratoconus had lower corneal thicknesses than in the eyes with stage 2 keratoconus. Moreover, Kmax was significantly higher in stage 3 keratoconus than in the stage 2 keratoconus in all age subgroups as expected. In summary, in pediatric keratoconus, ACD seems to increase with disease severity, whereas in adult patients with keratoconus, corneal parameters appear to worsen with progression. A similar report from Sahebjada et al. 19 demonstrated reduced corneal thicknesses (pupil center, apical and thinnest location) in the severe keratoconus group than in the mild keratoconus group.

  • Top
  • Abstract
  • Introduction
  • Methods
  • Results
  • Discussion
  • Conclusion
  • References
  • Conclusion
    In conclusion, shallowing in AC over time appears to affect both patients with keratoconus and normals; however, it can be suggested that patients with keratoconus in all age subgroups have deeper AC than in the healthy controls. Furthermore, an increase in ACD value might be indicative of progression in pediatric patients with keratoconus. Although corneal parameters seem not to differ between age-based keratoconus subgroups, in adult patients with keratoconus corneal thicknesses and volume can be monitored to detect disease progression. However, long-term prospective clinical trials are needed to demonstrate the changes in anterior segment measurements from a pediatric age to the adulthood.

    Acknowledgments
    No author has a financial or proprietary interest in any product, material, or method mentioned. No financial support was received for this study. The abstract of this study was presented at the XXXIII. Congress of the European Society of Cataract & Refractive Surgeons – ESCRS 2015 (5-9 September, Barcelona, Spain) as poster.

  • Top
  • Abstract
  • Introduction
  • Methods
  • Results
  • Discussion
  • Conclusion
  • References
  • References

    1) Rabinowitz YS. Keratoconus. Surv Ophthalmol 1998;42(4):297-319.

    2) Kankariya VP, Kymionis GD, Diakonis VF, et al. Management of pediatric keratoconus - evolving role of corneal collagen cross-linking: An update. Indian J Ophthalmol 2013;61(8):435-40.

    3) Toprak I, Yaylalı V, Yildirim C. Factors affecting outcomes of corneal collagen crosslinking treatment. Eye 2014;28(1):41-6.

    4) Vinciguerra P, Albé E, Frueh BE, Trazza S, Epstein D. Two-year corneal cross-linking results in patients younger than 18 years with documented progressive keratoconus. Am J Ophthalmol 2012;154(3):520-6.

    5) Caporossi A, Mazzotta C, Baiocchi S, Caporossi T, Denaro R, Balestrazzi A. Riboflavin-UVA-induced corneal collagen cross-linking in pediatric patients. Cornea 2012;31(3):227-31.

    6) Rabsilber TM, Khoramnia R, Auffarth GU. Anterior chamber measurements using Pentacam rotating Scheimpflug camera. J Cataract Refract Surg 2006;32(3):456-9.

    7) Belin MW, Ambrósio R. Scheimpflug imaging for keratoconus and ectatic disease. Indian J Ophthalmol 2013;61(8):401-6.

    8) Bühren J, Kook D, Yoon G, Kohnen T. Detection of subclinical keratoconus by using corneal anterior and posterior surface aberrations and thickness spatial profiles. Invest. Ophthalmol Vis Sci 2010;51(7):3424-32.

    9) Emre S, Doganay S, Yologlu S. Evaluation of anterior segment parameters in keratoconic eyes measured with the Pentacam system. J Cataract Refract Surg 2007;33(10):1708-12.

    10) Edmonds CR, Wung SF, Pemberton B, Surrett S. Comparison of anterior chamber depth of normal and keratoconus eyes using Scheimpflug photography. Eye Contact Lens 2009;35(3):120-2.

    11) Zadnik K, Barr JT, Gordon MO, Edrington TB. Biomicroscopic signs and disease severity in keratoconus. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Cornea 1996;15(2):139-46.

    12) Kamiya K, Ishii R, Shimizu K, Igarashi A. Evaluation of corneal elevation, pachymetry and keratometry in keratoconic eyes with respect to the stage of Amsler-Krumeich classification. Br J Ophthalmol 2014;98(4):459-63.

    13) Buehl W, Stojanac D, Sacu S, Drexler W, Findl O. Comparison of three methods of measuring corneal thickness and anterior chamber depth. Am J Ophthalmol 2006;141(1):7-12.

    14) Meinhardt B, Stachs O, Stave J, Beck R, Guthoff R. Evaluation of biometric methods for measuring the anterior chamber depth in the non-contact mode. Graefes Arch Clin Exp Ophthalmol 2006;244(5):559-64.

    15) Barkana Y, Gerber Y, Elbaz U, Schwartz S, Ken-Dror G, Avni I, et al. Central corneal thickness measurement with the Pentacam Scheimpflug system, optical low-coherence reflectometry pachymeter, and ultrasound pachymetry. J Cataract Refract Surg 2005;31(9):1729-35.

    16) Lackner B, Schmidinger G, Skorpik C. Validity and repeatability of anterior chamber depth measurements with Pentacam and Orbscan. Optom Vis Sci 2005;82(9):858-61.

    17) Kovacs I, Mihaltz K, Nemeth J, Nagy ZZ. Anterior chamber characteristics of keratoconus assessed by rotating Scheimpflug imaging. J Cataract Refract Surg 2010;36(7):1101-06.

    18) Fontes BM, Ambrosio R Jr, Jardim D, Velarde GC, Nosé W. Corneal biomechanical metrics and anterior segment parameters in mild keratoconus. Ophthalmology 2010;117(4):673-9.

    19) Sahebjada S, Xie J, Chan E, Snibson G, Daniel M, Baird PN. Assessment of anterior segment parameters of keratoconus eyes in an Australian population. Optom Vis Sci 2014;91(7):803-9.

    20) Xu L, Cao WF, Wang YX, Chen CX, Jonas JB. Anterior chamber depth and chamber angle and their associations with ocular and general parameters: the Beijing Eye Study. Am J Ophthalmol 2008;145(5):929-36.

  • Top
  • Abstract
  • Introduction
  • Methods
  • Results
  • Discussion
  • Conclusion
  • References
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