Differentiating Keratoconus and Corneal Warpage by Analyzing Focal Change Patterns in Corneal Topography, Pachymetry, and Epithelial. Cont Lens Anterior Eye. Sep;26(3) Hydrogel contact lens-induced corneal warpage. Schornack M(1). Author information: (1)Department of. Before the advent of corneal topography, corneal warpage was generally described as a condition that included distorted keratometer mires.
|Published (Last):||25 September 2017|
|PDF File Size:||14.78 Mb|
|ePub File Size:||6.19 Mb|
|Price:||Free* [*Free Regsitration Required]|
To differentiate between keratoconus and contact lens-related corneal warpage by combining focal change patterns in anterior corneal topography, pachymetry, and epithelial thickness maps.
Pachymetry and epithelial thickness maps of normal, keratoconus, and warpage, and forme fruste keratoconus FFK eyes were obtained from a Fourier-domain optical coherence tomography OCT.
Corneall pattern standard deviation PSD was calculated and combined with two novel indices, the Warpage Index and the Anterior Ectasia Index, to differentiate between normal, keratoconus, and warpage eyes.
The values of the three parameters were compared between groups. The study included 22 normal, 31 keratoconic, 11 warpage, and 8 FFK eyes.
The Anterior Ectasia Index of normal eyes 1.
The Warpage Index was positive in all warpage eyes and negative for all keratoconic and FFK eyes except three wearing rigid gas-permeable contact lens.
The epithelial PSD can distinguish normal from keratoconus or warpage, but does not distinguish between these two conditions. The Anterior Ectasia Index is crneal in keratoconus but not warpage. The Warpage Index is positive for warpage and negative for keratoconus, except in cases where keratoconus and warpage coexist.
Together, the three parameters are strong tripartite discriminators of normal, keratoconus, and warpage. Warpag this article with an account. Louie ; Julie M. Schallhorn ; David Huang. You will receive an email whenever this article is corrected, updated, or cited in the cprneal. You can manage this and all other alerts in My Account. This feature is available to authenticated ckrneal only. Placido disc topography is an important tool in the recognition of forme fruste keratoconus FFK12 which is the most important risk factor for post-LASIK ectasia.
Several new tools have been developed to make the detection of FFK more reliable. The mean curvature a. More recent studies have shown that corneal pachymetry 5 — 8 and epithelial thickness maps 9 — 13 can be more sensitive than Placido topography for keratoconus diagnosis. On their own, these maps cannot differentiate keratoconus from other corneal pathologies with similar topographic patterns, such as contact lens-related warpage, dry eye disease, and epithelial basement croneal dystrophy.
Hydrogel contact lens-induced corneal warpage.
Because many LASIK candidates are contact lens wearers, the distinction between warpage and keratoconus is a common clinical challenge. The purpose of this study is to differentiate keratoconus from contact lens-related warpage by combining focal change patterns of several corneal warapge Two novel diagnostic indices were developed to aid in the differential awrpage of corneal conditions that confront the corneal and refractive surgeon.
Warpafe prospective observational study was approved by the institutional review board of the Casey Eye Institute, Portland, Oregon, United States. This work is compliant with the Health Insurance Portability and Accountability Act of and adhered to the tenets of the Declaration of Conreal.
Normal subjects enrolled in this study were LASIK candidates who had no ocular diseases and have not been wearing contact lenses for at least 2 weeks prior to the exams. Keratoconus subjects included in this awrpage were diagnosed clinically with the following inclusion criteria: Eyes with late keratoconic changes such as corneal scars or hydrops were excluded as they did not pose any diagnostic challenge.
Keratoconus participants were subdivided into those who used rigid gas-permeable RGP and those who did not. There were no keratoconus participants who used soft contact lens.
Contact lens warpage was defined as contact lens wearers with topographic abnormality. The topographic abnormality included inferior—superior asymmetry greater than 1.
The FFK cases in the study were the better eyes of asymmetric keratoconus subjects.
Ectasia or permanent corneal warpage?
This system projects 40 optical slits, 20 from the right and 20 from the left, onto the cornea at a degree angle. The resulting slit images were captured by a digital video camera and used to reconstruct the topography of corneal surface. The topography maps were repositioned to be centered on the pupil center. The system works at an nm wavelength and has a scanning speed of 26, axial scans per second.
Hydrogel contact lens-induced corneal warpage.
The pachymetry and epithelial thickness maps were also centered on the pupil center. The pattern deviation PD map was defined as the percent deviation from the normal reference map i. It can be calculated from topography maps, pachymetry, or epithelial thickness maps.
The detailed calculation method of the PD map have been described in a previous study. The Warpage Index was designed based on the insight that anterior focal steepening is accompanied by focal epithelial thickening in cornsal lens-related warpage, but associated with epithelial thinning in keratoconus Table 1.
It is calculated by the dot product of the PD maps of anterior topography and epithelial thickness Equation 1. View Original Download Slide. Contact lens-related warpage top and keratoconus bottom are not distinguishable by anterior topography i.
They can be differentiated by the OCT epithelial map, which shows matching focal thickening in warpage and thinning in keratoconus. The pachymetry map shows focal thinning corneql keratoconus, but not in warpage. The warpage map is the product of the PD maps of anterior topography and epithelial thickness. The ectasia map is the product of fitted Gaussian waveforms for the PD maps of anterior topography and pachymetry.
It shows clear cone-like pattern in keratoconus, which is absent in warpage. Although a negative Warpage Index was consistent with keratoconus, we wanted to incorporate the pachymetry map information to further confirm the classification. We used the Gaussian waveform, which was cone shaped, to fit the focal ectasia.
A generalized estimation equation model 16 was used to account for the correlation between the eyes of cornral same subject. Kruskal-Wallis nonparametric tests were used to compare different groups. The study included 31 keratoconic eyes 19 of which had recent RGP wear of 20 subjects, 22 normal cornela of 11 subjects, 11 eyes six eyes wearing RGP, five eyes wearing soft toric contact lenses of eight subjects with contact lens-related corneal warpage and eight FFK eyes four of which had recent RGP wear of eight subjects.
There was no difference in age between groups Table 2. The minimum epithelial thickness in the keratoconus group was significantly lower than that in the normal group but was not different from that in the warpage or the FFK group.
Ectasia or permanent corneal warpage? | Defeat Keratoconus
The epithelial PSD was normal 0. There was no difference in mean epithelial PSD values between eyes with RGP contact lens-induced warpage and eyes with soft toric contact lens-induced warpage. The Anterior Ectasia Index for the normal group 1. Using Anterior Ectasia Index of 6.
The pink area denotes keratoconus, while the blue area denotes warpage. The purple area indicates both conditions coexist. The Warpage Index was positive in all warpage coneal 3. A keratoconus case that also shows signs of contact-lens related warpage. Given that contact lenses are often used for vision correction in keratoconus, an overall diagnostic scheme is needed to account for this overlap.
We propose the use of a decision tree Fig. Those with negative Warpage Index values are diagnosed with keratoconus, while those with positive Warpage Index are diagnosed with warpage. The warpage cases are then tested with the Anterior Ectasia Index, with the result that the subthreshold cases has pure warpage, while the supra-threshold are diagnosed with both keratoconus and warpage.
Nine of the contact lens-related warpage cases were correctly classified One of the 19 RGP-corrected keratoconus eyes had mixed keratoconus plus warpage pattern, while in the other 18 the coreal pattern predominated. Five out of 8 FFK eyes Proposed approach for comprehensive keratoconus and warpage diagnosis in a clinical setting.
However, topography is not sensitive to very early stages of keratoconus when the topographic steepening is masked by focal epithelial thinning. We previously developed diagnostic parameters based on OCT corneal pachymetry and epithelial thickness maps to detect early keratoconus.
To specifically diagnose keratoconus, combining pattern analysis of focal changes in different maps is needed, as has been pointed out in the global consensus definition of keratoconus and ectasia. In this study, we developed the two novel indices, Anterior Ectasia Index and Warpage Index, to differentiate keratoconus from warpage by combining the focal changes in anterior corneal topography, pachymetry, and epithelial thickness maps. To date, all keratoconus diagnostic algorithms only attempt to distinguish keratoconus from normal eyes.
Our new approach is more closely tailored to the real-world application where a surgeon must distinguish between several different conditions warpaeg require different treatment decisions. An abnormally high Anterior Ectasia Index is the result warpaeg the coincident focal topographic steepening and pachymetric thinning, cornewl is typical in keratoconus and other ectasia i.
On the other hand, an abnormal i. It is interesting to note that most warpagd eyes have a small positive Warpage Index. We speculate that it might be caused by upper lid pressure molding the epithelial thickness, causing a normal pattern of slightly thinner superior epithelium and warpae flatter awrpage topography.
All warpage cases in our study were induced by RGP or soft toric contact lenses instead of regular soft spherical lenses, probably because RGP and soft toric contact lenses had more effect in changing the corneal epithelium. Using just one of the two new indices is not sufficient to distinguish between keratoconus and warpage. Though the Anterior Ectasia Index can separate the keratoconus and normal group perfectly, it does not differentiate between the warpage and normal group.
Similarly, though Warpage index is positive in all warpage eyes and normal in most keratoconus eyes, it fails in cases where keratoconus and warpage coexist. Tripartite classification between normal, warpage, and ectasia requires using both new indices together with the epithelial PSD. This is contrary to the positive Warpage Index we see in nonkeratoconic contact lens warpage. This is probably because epithelium at the cone peak comes into contact with the RGP contact lenses, resulting in epithelial thinning at a location of topography steepening—opposite of the usual warpage pattern where epithelial thinning is associated with focal topographic flattening.
Overall, in RGP-wearing keratoconus eyes, there is a paradoxical negative shift of the Warpage Index due to cone-apex RGP touch, except in the unusual case where the RGP-corneal contact is not at the cone apex. The main limitation of this study is that the number of cases is relatively small, which can be addressed in a future study with more cases. Another limitation is that if keratoconic distortion is extremely subtle e. If so, contact lens cessation will remain necessary for our classification scheme to accurately distinguish between keratoconus and warpage.
Additionally, the OCT scans used in this study only covered central 6-mm diameter corneal area. This limited its ability to detect peripheral corneal abnormalities. In summary, this study confirms that OCT-based epithelial PSD can detect corneal distortions with high sensitivity and specificity.