Keratoconus induced High Order Aberrations and Contact Lenses: S. Barry Eiden, OD, FAAO, FSLS
President and Co-founder – International Keratoconus Academy of Eye Care Professionals
Acknowledgement: The GP Lens Institute would like to acknowledge the assistance of the International Keratoconus Academy of Eye Care Professionals for assistance in the keratoconus section
A 63-year-old male presented for contact lens management of his previously diagnosed keratoconus. He was initially diagnosed at age 35 and had been fit in various designs of gas permeable corneal contact lenses with variable success. The patient felt that he has only tolerated his contact lenses over the years and has reported relative discomfort without fitting success. He presented with relatively flat fitting lenses that demonstrated limited movement with the blink. The patient also reported that vision, although stable with contact lenses for many years, had become noticeably poorer over the past 2 to 3 years. There were symptoms of glare and halos around light sources which were more pronounced in dark environments. Findings and outcomes from the right eye are presented; however, findings and management were quite symmetric between the right and left eyes.
The results of a comprehensive diagnostic consultation found a manifest refraction of -6.50 – 5.00 x 015 with visual acuity of 20/30-3. Biomicroscopy showed +1 Vogt’s striae, an obvious Fleischer’s ring, and very subtle apical anterior stromal corneal scar formation. There was no significant corneal staining noted. There were involutional lens changes which were graded subjectively as +1 nuclear sclerosis and anterior cortical.
Scheimpflug corneal tomography (Pentacam, Oculus) was performed that indicated a classic keratoconic profile of anterior corneal curvature, anterior and posterior corneal elevation anomalies and global pachymetry that was apically thin with significant pachymetric progression abnormality (i.e. a rapid rate of relative thickening from the thin point out to the periphery). The pattern was typical of a fairly well-centered cone apex.
Key Pentacam Metrics:
- K-Max: 55 diopters
- Anterior corneal apical elevation: 26 microns anterior to the reference sphere (normal up to approximately 8 microns
- Posterior corneal apical elevation: 64 microns anterior to the reference sphere (normal up to approximately 14 microns)
- Corneal thinnest point: 434 microns
Integrated aberrometry was performed (OPD-3 Marco) without the presence of contact lenses. Expected elevation of anterior, internal, and total high order aberrations (HOAs) was discovered.
Key OPD-3 Metrics with no lens in place:
- Total RMS at 3mm zone: 1.43 (normal up to 0.35)
- Total RMS at 6mm zone: 1. 39 (normal up 0.60)
- Elevation of BOTH anterior and internal HOAs (primarily trefoil and oblique coma)
Contact Lens Management
A refitting of corneal GP lenses was performed with the expressed goal of lens clearance above the anterior apex of the cone. This was accomplished with the use of a bi-aspheric GP design obtained via diagnostic lens fitting according to the manufacturers fitting guide. The lens-to-cornea fitting relationship showed good centration, mild apical clearance, peripheral alignment, and adequate edge lift and movement with the blink. A sphero-cylinder over-refraction resulted in visual acuities of 20/20-3. The patient felt his vision was superior to his habitual contact lens; however, there was still some degree of blur and some distortion.
Aberrometry was again performed, but this time with the contact lens in place. There was a dramatic reduction of anterior HOAs based on the masking influence of the contact lens; however, there was still some residual elevation of internal HOAs due to both the posterior corneal surface irregularity and the age-related lenticular changes. These internal HOAs were the primary contributors to the elevation of total HOAs and likely also related to the subjective symptoms experienced through the new contact lens.
Patient Consultation and Education
There were a number of key points here that were reviewed and discussed with the patient in advance of moving forward with the contact lens refitting. First was a review of the disease state. We clearly advised the patient that based on his age that progression of his keratoconic disease was highly unlikely. That being said, we did review family history and found out that the patient had a brother with keratoconus. The patient also had three children ages 29, 27 and 21. It was impressed upon the patient that all of his children should be screened for keratoconus with advanced diagnostic technologies that could detect keratoconic corneal changes prior to subjective vision loss. It was made clear that today with the advent of technologies such as corneal cross linking, early diagnosis and treatment of keratoconus can preserve normal visual function. Second, we discussed the impact of ill-fitting corneal contact lenses on the health of a keratoconic cornea. We informed the patient that flat-fitting corneal gas permeable contact lenses likely increase the risk of developing progressive corneal scarring which could result in loss of vision and increase the likelihood of needing a corneal transplant. Third, we utilized images from both Scheimpflug corneal tomography (Pentacam) and integrated aberrometry (OPD-3) to educate the patient on the expected visual outcomes of the most properly prescribed contact lens. By showing the patient images of posterior corneal shape irregularity as well as lenticular translucencies and linking them to images of point spread functions we were able to explain why there still will be some visual dysfunction after an optimal contact lens fitting. Following this extensive patient educational effort, the patient stated that he understood his situation and agreed to moving forward with refitting of his corneal gas permeable contact lenses.
Follow-Up Care/Final Outcomes
As expected from the results of the initial cornea and contact lens diagnostic consultation and contact lens refitting, the patient’s new contact lenses provided improved – but not perfect -visual outcomes. Physical comfort and wearability with the new contact lenses were significantly improved as well. Follow-up care was conducted one week, one month, three months and six months following initial dispensing of lenses. Ongoing follow-up will be conducted on an annual basis until progressive cataract formation will result in the need for surgery. This will open up a totally new “can of worms”!
This case demonstrates the importance of understanding the natural history and course of keratoconus, its genetic impact, and the impact of contact lenses both on the visual performance as well as physiological outcomes in the disease. It further demonstrates the clear understanding of visual impact of both the posterior cornea and other optical elements internal to the anterior corneal irregularity well known in keratoconus.
A comprehensive approach to keratoconus management is key to providing optimal patient care. This approach must address the following:
- Understanding pathophysiology of the disease
- Understanding the natural course of the disease and its variability
- Understanding the relative risk of progression in keratoconus and the importance of early detection via advanced diagnostic technologies
- Understanding of technologies that can slow or often halt progression of the disease and when these technologies should be implemented (and when they should not)
- Understanding the visual impact of keratoconus and the various methods to improve visual function (optical correction alternatives, medical therapeutic alternatives, and surgical alternatives)
- Understanding the importance of looking beyond the patient based on hereditary aspects of the disease
- Jinabhai A, Radhakrishnan H, O’Donnell C. Higher-Order Aberrations in Keratoconus: A Review. Optometry in Practice 2009;10:141–160.
- Saad A, Gatinel D. Evaluation of Total and Corneal Wavefront High Order Aberrations for the Detection of Forme Fruste Keratoconus. Invest Ophthalmol Vis Sci 2012;53(5):2978-2992.
- Shi Y. Strategies for improving the early diagnosis of keratoconus. Clinical Optometry 2016;8: 13-21.
Back to Table of Contents