A recent study published in the Journal of Ophthalmology evaluated the applicability of an algorithm developed for keratoconus (KC) detection in adolescents that uses anterior segment optical coherence tomography (ASOCT) to assess changes in corneal pachymetry and epithelial thickness.
Give me some background.
KC is a progressive corneal ectasia that usually begins during adolescence and has a faster rate of progression in children that can lead to poorer visual outcomes.
As such, it is critical that pediatric patients receive an early diagnosis of KC with reliable clinical tests.
Now bring in ASOCT.
Scheimpflug imaging is the most commonly used approach to diagnose KC because it can evaluate the anterior surface curvature and posterior corneal elevation as well as measure corneal pachymetry.
Recent studies have shown that identifying coincident thinning of the cornea and epithelium alongside concentric epithelial thinning can improve the specificity and sensitivity of the detection of KC.
ASOCT can be used to detect KC with corneal pachymetric and epithelial thickness maps—though so far this has only been verified in adult patients.
Now the study.
In this retrospective review, researchers included 19 patients under the age of 18 diagnosed with KC in the analysis.
Participants were organized into four subgroups according to the Belin-Ambrosio display (Pentacam):
- Normal
- Manifest
- Subclinical KC
- Very asymmetric eye with normal topography and tomography (VAE-NTT)
The Belin-Ambrosio Enhanced Ectasia display measures corneal topography and has in the past been used to determine the level of corneal ectasia.
Of note: Investigators also analyzed 22 eyes from 11 normal adolescents; the corneal and epithelial thickness maps were evaluated by human graders.
How did the algorithm work?
In the first step, if at least one of the four parameters below exceeded its cut-off value, the eye was considered suspect:
- Pachymetry minimum (pachy min) <513μm
- Pachy minimum-median (min-med) < -24μm
- Pachy superonasal-inferotemporal (SN-IT) >32μm
- Epithelial SN-IT (epi SN-IT) >1μm
Note: Epi SN-IT measures epithelial thinning; it is the average epithelial thickness of the superonasal octant minus the average epithelial thickness of the inferotemporal octant between the 2 mm and 5 mm diameter rings.
And in the next step?
The combined presence of coincident thinning of the total cornea and epithelium as well as concentric epithelial thinning led to a diagnosis of KC.
Investigators determined the area under the receiver operating characteristic curve (AUROC) to assess the parameters' sensitivity and specificity.
Meaning: AUROC is a metric for measuring a model’s ability to discriminate between cases and non-cases; the closer to 1.00 the AUROC is, the better the model is at discerning between cases and non-cases.
Findings?
The research team classified the cohort of 19 pediatric patients with KC as follows:
- 29 eyes with manifest KC
- 3 eyes subclinical KC
- 5 VAE-NTT eyes
Note: The AUROC values of the parameters from step 1 were as follows:
- 0.889 pachy min
- 0.997 pachy min-med
- 0.893 pachy SN-IT
- 0.998 epi SN-IT
Anything else?
When both steps of the algorithm were performed, it captured all manifest and subclinical pediatric keratoconic eyes.
Further, when all eyes of the KC patients were combined, step 1 had 97.3% sensitivity and step 2 had 100% specificity.
Limitations?
Key limitations included the study’s retrospective design and lack of follow-up.
The study authors also noted that if VAE-NTT had been followed up, it may have developed to manifest KC and the small sample size may have prevented the study from developing more robust findings.
Take home.
Using an algorithm that features corneal pachymetry and epithelial thickness changes measured with ASOCT in adolescents resulted in a high level of agreement with tomography.
The conclusion: Using this algorithm with other examinations may improve the diagnostic accuracy of KC in pediatric patients.