Pediatric keratoconus is often more challenging to diagnose, resulting in treatment delay and vision loss.
Myopia has long been defined as a dioptric diagnosis of refractive error. Because of the seemingly benign presentation, myopia has yet to be classified as a disease. Growing research, however, has supported and validated that the underlying etiology of myopia predominantly stems from axial elongation of the globe.1,2
The younger the age at which the onset of myopia occurs, the more rapid the progression of myopia. Because of its early onset, the potential odds of developing lifelong ocular complications can be significant in adulthood, which can be detrimental to overall ocular health.1,2 Myopia affected 30% of the global population in 2020. That percentage is estimated to rise to 50% by 2050, when 5 billion individuals
worldwide will likely develop myopia.3
Keratoconus is known as a bilateral, noninflammatory ectatic corneal disorder characterized by progressive stromal thinning, corneal irregularities, and permanent vision loss if left unmanaged. It is associated with progressive myopia. Currently, the estimated global prevalence in the general population is approximately 1 in 375 to 1 in 2000 individuals, depending on the testing used.4-6
Patients with keratoconus are generally younger, with male patients having a higher ratio of advanced keratoconus compared with female patients.6,7 Keratoconus has been reported in children with Down syndrome as young as 4 years.8 Distinct clinical signs, such as corneal steepening or thinning, Vogt striae (Figure 1), Fleischer ring, or Munson sign,9,10 may not manifest in the early stages in the pediatric population. Because of inadequate or inconclusive clinical signs, cases of keratoconus are largely underdiagnosed in pediatric patients.6,11 Corneal topographical analysis provides an earlier indication for which progression can be screened and monitored periodically.
At first glance, the nature of myopia may not seem to share similarities with keratoconus. Research suggests the onset and development of myopia may be implicated by different stages of corneal biomechanical variabilities. Decreased corneal stiffness was found in patients with progressing myopia.12,13 The intricate relationship between myopia and keratoconus may be more common than initially expected. A study investigated the association between keratoconus and axial myopia.14
Biometric parameters were compared between eyes diagnosed with keratoconus and eyes with emmetropia serving as controls. Significantly greater axial length was found in eyes with keratoconus compared with eyes with emmetropia (23.97 vs 23.21 mm; P < .001). A similar pattern was noted for posterior segment length between the 2 groups (16.54 vs 15.99 mm; P < .001). A strong positive association between posterior segment length and spherical equivalent refractive error suggested that keratoconus likely shares some levels of pathophysiological etiology with axial myopia.
Practical considerations may be warranted for patients with keratoconus and myopia undergoing surgical interventions, such as penetrating keratoplasty (PK), because longer axial lengths of eyes with keratoconus may affect postoperative refractive outcomes.15 Nevertheless, the development of axial myopia was shown to continue upon postoperative PK for keratoconus, suggestive of possible independent pathways upon the initial onset.16
Clinicians following young patients with myopia using myopia control programs see patients regularly and are likely to note changes in manifest refraction, contact lens fitting parameters, corneal topography, and best corrected vision that may indicate keratoconus. It is important to keep early signs of keratoconus in mind to identify patients prior to vision loss. Pediatric keratoconus shares many signs and symptoms of adult keratoconus.
However, it is more progressive at a younger age17 and more aggressive than adult keratoconus.6,10 Al Suhaibani et al reported that the severity of keratoconus is inversely associated with the age of onset.18 Léoni-Mesplié et
al assessed 216 patients with keratoconus, including 49 patients 15 years or younger.19 At initial diagnosis, 27.8% of the pediatric group had stage IV keratoconus using the Amsler-Krumeich classification whereas 7.8% in the adult group had stage IV keratoconus.
Findings from a retrospective study by El-Khoury et al found that 541 patients received a diagnosis of keratoconus over a 5-year period. Sixteen were children younger than 14 years who presented for routine care (n=1 patient), allergic conjunctivitis (n=3), reduced vision (n=10), and corneal hydrops (n = 2).20 Olivo-Payne et al suggested that children have a higher risk of acute corneal hydrops, leading to an increased need for corneal transplantation to improve vision.11 Early detection and timely treatments are paramount to halt progression and prevent severe vision impairment for children.
Key clinical indicators of developing keratoconus in children include higher average central corneal keratometry (vs periphery), increased posterior corneal elevation, and thinner corneal thickness.10 Keratoconus in children may manifest differently than in adults. The cornea ectasia location was reported to be located more centrally among pediatric patients.21 In these cases, the extent of irregular astigmatism is generally less pronounced, so visual acuity is not significantly affected and should not be used as an indicator. Young patients tend to show few symptoms until the keratoconus deteriorates bilaterally.
Keratoconus is generally more prevalent in those with atopic eye disorders, including vernal keratoconjunctivitis (VKC) and seasonal allergic conjunctivitis (SAC).22 Gupta et al evaluated patients with keratoconus younger than 18 years using visual acuity, corneal topography, aberrometry, and biomechanical and confocal microscopy.23One hundred sixteen eyes of 62 consecutive patients (mean age ± SD, 14.7 ± 2.77 years; range, 8-18 years) were studied; 88% of patients were male, and 92% demonstrated bilateral disease. Although systemic associations were identified in 9.7%
of patients, ocular associations were identified in 66.3%, including VKC in 58.6%. Among eyes with VKC, 29 of 68 eyes (46%) were in stage IV of the disease vs 25% of eyes with no VKC (P=.004).
Naderan et al prospectively investigated allergic diseases among patients with keratoconus.24 They evaluated 885 patients with keratoconus, comparing them with 1526 control patients and looking for various allergic diseases. They found significantly thinner and steeper corneas in patients with keratoconus and VKC or SAC compared with nonallergic patients with KC. They recommended this subpopulation be followed more closely.
Five hundred thirty cases of VKC were studied in Pakistan.25Corneal complications occurred in 259 patients, including 48 patients with keratoconus (41 male, 7 female). Thirty-seven of 48 patients were aged between 10 and 30 years. Six patients developed acute hydrops, with 1 bilateral case.
Results from other studies found that patients with VKC or SAC displayed significantly distinct corneal and biomechanical features, notably steeper and thinner corneas compared with the nonallergic group with keratoconus.26 This suggests that this subpopulation experiencing atopic disease is particularly susceptible to severe keratoconus.
Not surprisingly, younger patients with VKC or SAC tend to show higher behavioral dependency of eye rubbing to alleviate the symptoms. Meta-analyses and reviews revealed consistent associations with the progression of keratoconus.27,28
Chronic corneal epithelial degradation from matrix metalloproteinases (MMPs) have been blamed for keratoconus progression.29,30 MMP levels are often elevated because of allergic and vernal conjunctivitis. As a result, chronic corneal epithelial degradation secondary to MMP level elevation has been considered an etiology of rapid progression of keratoconusin children.
In addition, corneal ectasia is likely associated with IgE-driven cascade events that trigger extracellular matrix remodeling and chronic inflammatory reaction on the cornea. Patients experiencing VKC or SAC need to be monitored using corneal topography to identify keratoconus in early stages.
Pediatric keratoconus is often more challenging to diagnose, resulting in treatment delay and vision loss. For mild to moderate ectasia, corneal cross-linking is recommended to halt progression. Scleral lenses are a great tool for visual rehabilitation and may be used for pediatric patients as young as 7 months with remarkable outcomes.31,32 For severe cases in which keratoconus and corneal scarring is involved, corneal keratoplasty is likely warranted to aid visual rehabilitation and preserve vision.
Kevin Chan, OD, MS, FAAO, is the senior clinical director of Treehouse Eyes and currently serves as a professional affairs consultant for Johnson & Johnson Vision and Essilor’s Myopia Taskforce. Notably, Chan has starred in the renowned TEDx talk titled, “Myopia - Global Epidemic.” firstname.lastname@example.org
Tracy L. Schroeder Swartz, OD, MS, FAAO, Dipl ABO is in group optometric practice in Madison, AL. email@example.com