Specialty Contact Lenses for Management of Keratoconus
Title: Specialty Contact Lenses for Management of Keratoconus
Author (s): Joanne Chan OD, David Meyer OD FAAO
Date: 07/18/2023
Keywords/Main Subjects: Contact lenses; Keratoconus; Topography; Scleral contact lens; RGP; Hybrid contact lens
Introduction
Keratoconus is a bilateral eye condition described as a progressive thinning of the cornea. This disorder leads to a protrusion of the cornea in a cone-like fashion resulting in irregularities to its surface and high myopic irregular astigmatism. It appears most frequently within the first three decades of life and is thought to be somewhat hereditary as one in 10 keratoconus patients has a family member with the condition. Several other environmental factors can cause its development, including eye rubbing from chronic ocular inflammation along with seasonal allergies and asthma. Although there is no cure for the condition, preventing further progression and improving visual acuity is the mainstay treatment. Modern technology has improved in its management of keratoconus allowing patients a large array of specialty contact lens options. These lenses can deliver clearer vision to the patient and potentially delay the need for a corneal transplant in certain cases.
Diagnosis of Signs and Symptoms
The best way to detect keratoconus is to have annual examinations with an eye doctor and to be able to recognize the symptomology of the condition. Keratoconus patients may experience blurring of vision that is changing rapidly and more frequently in their early adult years that cannot be fully corrected with glasses or traditional soft contact lenses. They may experience distorted vision, increased light sensitivity, glare, and halos. It is pertinent to ask if the patient frequently rubs their eyes as there is a strong association with eye-rubbing, seasonal allergies, and prevalence of keratoconus.
In office, the doctor will perform a series of tests to detect signs of keratoconus. The primary diagnostic tool utilized is the topographical map of the cornea to look for any areas of ectasia. Topography is performed annually and referred to frequently if there is any suspicion of progression. This is also an important test used in the fitting of contact lenses.
Use of Specialty Contact Lenses
Spectacles or traditional soft contact lenses may be a treatment modality for patients with mild cases of keratoconus, but most patients require specialty contact lenses to give them clear, comfortable vision. Specialty gas-permeable contact lenses provide the best visual success for moderate to severe keratoconus patients, because it reduces higher order aberrations and masks the irregular anterior corneal surface. The combination of the lens acting as a smooth optical surface and the intervening tear layer from the creation of the lens and cornea allows for the best optimal refraction of light. Fortunately, there is a large variety of lens designs that can fit any patient. Options range from corneal rigid gas permeable, scleral, hybrid, to custom soft lenses.
Specialty contact lens fittings regardless of lens design are fairly similar in their examination. In some cases, the optometrist may decide to design the contact lens empirically, but most patients can expect the doctor to perform the examination diagnostically with a series of trial lenses from a fitting set. After choosing the initial lens and allowing it to settle for a few minutes, a measurement of visual acuity, over-refraction, and fitting of the lens behind the slit lamp is performed to achieve the ideal lens. The practitioner will then take these measurements post-examination and design a custom lens that is tailored to fit the patient’s cornea. When the lens arrives, the patient will learn proper care and insertion and removal techniques. The patient will then return for a follow-up visit to ensure that the lens is fitting well and providing comfortable, clear vision. At this visit, additional measurements and changes are often made to ensure the best fitting lens and optimal visual outcome. Typically, patients should expect at least one follow-up visit after the initial fitting, but two visits are more common.
Good compliance with follow-up visits is important for optimal visual success and management of keratoconus. This is a condition that is progressive and may change the vision and shape of the cornea from year to year, ultimately changing its interaction with the power and fit of the contact lens. It is pertinent for the patient to continue with bi-annual examinations with the doctor to ensure the best fitting lens that gives the best vision. Together with corneal crosslinking procedures used to slow down progression, specialty contact lenses can serve as a great asset to patients who may find keratoconus otherwise debilitating to their quality of life.
Types of Specialty Contact Lenses
Corneal Rigid Gas Permeable Lenses (RGP)
This option is one of the most widely used and traditional treatment modalities for patients with keratoconus. Corneal RGPs are defined as lenses that rest solely on the cornea and can vary in size from 7-10mm in diameter. The main advantages of this type of lens is easy maintenance and clear vision that is usually superior to any type of soft lens. The disadvantage of these lenses is they tend to be less comfortable and are prone to allowing foreign objects such as dust to induce significant discomfort. Despite its discomfort, many patients adapt to the lenses and enjoy their ease of use.
Using the K-readings from the topography, the doctor will choose a lens about 0.75D flatter than the average-K and place it on the eye. Fluorescein dye and a cobalt blue filter is used to assess the lens fit. The fit shouldn’t be excessively touching or clearing over the cornea; instead, there should be a feathery touch-like appearance. They should be well aligned to the cornea and have good movement upon blink.
Scleral Lenses
Scleral lenses have been gaining popularity in recent years because of their ability to center better on the eye and provide improved comfort while maintaining clear visual acuity. Scleral lenses are contact lenses that vault over the entirety of the corneal surface and limbus and rest on the sclera. These lenses are more comfortable because the conjunctiva is less sensitive than the cornea, and the large diameter reduces the effect of lens edge and lid interaction. Additionally, the lens is filled with preservative free saline solution that bathes the eye when it is worn, improving any ocular surface disease symptomology. The large vault can easily mask irregularities of a steep cornea and its large diameter allows for better stability.
The ideal lens fit should be clearing the corneal surface but not vaulting over the eye excessively. The edges should align seamlessly with the sclera, careful to not be too tight or loose which may cause discomfort to the patient.
However, with any lens, there are potential disadvantages. This lens can be burdensome to wear because of the steep learning curve that comes with inserting and removing the large-diameter lens. Prior to considering fitting patients into scleral lenses, it is important to consider the patient’s lid anatomy and their dexterity as that may be a barrier to success. However, if the patient is highly motivated, most patients of any age have the ability to wear scleral lenses.
Despite these disadvantages, scleral lenses play a pivotal role in current keratoconus management. In many instances, scleral lenses can reduce the need for a corneal transplant in severe keratoconus patients. Patients who would otherwise fail out of corneal RGPs because of discomfort or poor fit can now be presented with the option of scleral lenses to help improve their vision and comfort.
Hybrid Lenses
Hybrid lenses are an alternative solution to both of the lenses stated above. These lenses consist of a rigid center with a surrounding soft “skirt” and are designed to have minimal vault over the cornea. They tend to center better because of the skirt resting on the sclera, which makes them more comfortable than most RGPs. They are primarily used when the patient prefers the optics of an RGP but cannot adapt to the discomfort of the lens. Other indications would be if the patient has irregularities on the sclera such as a large pinguecula or a bleb.
Custom Soft Lenses
Patients who are experiencing unacceptable vision or discomfort from gas-permeable lenses can utilize custom soft lenses. Most “traditional” soft lenses are mass produced and have a limited number of parameters that may not fit every patient, especially a keratoconus patient. Custom soft lenses are made to order and can vary in different powers and base curves to fit the patient’s specific needs and corneal anatomy. The additional benefit is that they are similar to traditional soft lenses in the way of insertion, removal, care and comfort. The main disadvantage of soft lenses is often the inability to achieve acceptable vision, as the soft lens tends to “drape” over the irregular cornea. However, if the patient has mild keratoconus and their corneal surface isn’t extremely irregular or steep, then this would be a great option to consider.
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References
- Koppen, C., Kreps, E. O., Anthonissen, L., Van Hoey, M., Dhubhghaill, S. N., & Vermeulen, L. (2018). Scleral Lenses Reduce the Need for Corneal Transplants in Severe Keratoconus. American Journal of Ophthalmology, 185, 43–47. https://doi.org/10.1016/j.ajo.2017.10.022
- Ortiz-Toquero, S., Rodriguez, G., & Martin, R. (2021). Clinical guidelines for the management of keratoconus patients with gas permeable contact lenses based on expert consensus and available evidence. Current Opinion in Ophthalmology, 32(2), S1–S11. https://doi.org/10.1097/icu.0000000000000728
- Santodomingo-Rubido, J., Carracedo, G., Suzaki, A., Villa-Collar, C., Vincent, S. J., & Wolffsohn, J. S. (2022). Keratoconus: An updated review. Contact Lens and Anterior Eye, 45(3), 101559. https://doi.org/10.1016/j.clae.2021.101559
- Zhang, X. (2020). Effect of rigid gas permeable contact lens on keratoconus progression: a review. International Journal of Ophthalmology, 13(7), 1124–1131. https://doi.org/10.18240/ijo.2020.07.17
Faculty Approval by: Dr. Griffin Jardine
Copyright Joanne Chan, OD, David Meyer, OD, FAAO, ©2023. For further information regarding the rights to this collection, please visit: http://morancore.utah.edu/terms-of-use/
