Achieving Success With Soft Lenses
for Patients With Keratoconus

Optometrist specialized in medical contact lens fitting - Oculenti Contactlenzen (the Netherlands)

Introduction

Rigid lenses have been the traditional choice to provide patients who have keratoconus with improved vision when the visual acuity (VA) with spectacles is no longer sufficient [1]. However, rigid lenses can be uncomfortable and challenging to wear for patients with keratoconus due to lens intolerance resulting from irritation to both the eyelid and the anterior surface of the cornea [2]. When keratometric values exceed 52D (6.50mm), the vision-related quality of life with rigid lenses worsens significantly [3]. Patients who become or are intolerant to rigid lenses, with or without a multiple-curve design, can be fitted with alternative options these include piggyback, hybrid, scleral and, maybe undervalued, specialty soft lenses [1].

The only contact lenses that are not considered suitable for individuals with keratoconus are standard soft lenses, because they conform to the cornea's irregular shape due to their thinness and flexibility [1]. In contrast, rigid, hybrid and scleral lenses have a regular front surface that provides superior visual correction [1,2]. However, sometimes there are patients for whom you would prefer to fit a soft lens for various reasons. Fortunately, advancements in specialty soft lenses have made it possible to achieve a VA comparable to that with rigid, hybrid and scleral lenses. This article will briefly explain the design of these specialty soft lenses, will discuss two case reports to illustrate this and will highlight a few considerations when starting to fit these designs.

New Developments

Manufacturers have put significant effort into developing specialty soft lenses that maintain a regular front surface while on the eye. To achieve this, these lenses have increased centre thickness, and an aspheric front curve is typically used to optimise VA while the peripheral zone is thinner to increase oxygen supply and improve comfort [2,4]. This design enables these lenses to provide a vision correction equal to that with rigid corneal lenses when the keratoconus is in an early or moderate stage [1] even in more advanced cases, these lenses can sometimes provide a viable alternative [5], as demonstrated below.

Case 1: Early Keratoconus

A 29-year-old male with autism was referred to our clinic for contact lenses because he was diagnosed with keratoconus OS>OD. He expressed concerns about the comfort of contact lenses and noted that he would not wear lenses if they caused any discomfort.

BCVA with refraction: OD 0.9 / OS 0.6

Refraction: OD S-3.50=C-0.75x75 / OS S-1.75=C-1.50x137

Specialty soft lens:

Kerasoft IC

OD 8.6 / S-3.25=C-1.00x45 / periphery standard / 14.5

OS 8.6 / S-2.25=C-0.75x155 / periphery flat 1 / 14.5

BCVA with lenses: OD 1.0 / OS 1.0 / OU 1.2

With Kerasoft IC, it is possible to adjust the periphery. This is useful when the best-corrected VA is achieved with BCR ‘X’ but the best fit is achieved with BCR ‘Y’. These two curves can then be combined by changing the periphery. The periphery can be made steeper or flatter in 4 steps, each step representing a 0.2mm change. It is also possible to make quadrant-specific changes to the periphery. With Kerasoft IC it is possible to adjust the periphery. The periphery can be made steeper or flatter in 4 steps, each step representing 0.2mm change. It is also possible to make quadrant-specific changes to the periphery. The patient found the contact lenses comfortable and was happy with the improvement of his visual acuity. He made the decision to commence wearing contact lenses.

Case 1: Pentacam images OD (top) and OS

Case 2: Advanced Keratoconus

A 25-year-old male with advanced keratoconus OD and early keratoconus OS was fitted with a scleral lens OD. Because the VA OS is excellent (1.0) without correction, the patient is not using any form of correction for that eye. Due to the advanced keratoconus OD, the patient needed to be fit with a scleral lens with a high total sagittal depth. The apex of the lens pushed “up” the upper eyelid OD, creating a much larger aperture size OD than OS and a suboptimal cosmetic effect. He asked to be fitted with an alternative.

When we refitted him from the scleral lens (see parameters below) to a soft lens with increased centre thickness, the visual acuity remained remarkably the same, while the asymmetric lid aperture problem was resolved.

Old scleral lens:
Production of Oculenti Contactlenzen total sag.7100um, Diam. 18.0 BCVA scleral: 0.45

Specialty soft lens:

Novakone

BCR 5.00, periphery 8.20, IT3, S-21.50=C-2.50x30, Diam. 15.0

BCVA with lenses: 0.45

The design of the Novakone is adjustable in central thickness to ensure that the irregularity of the cornea can be well compensated. The thickness can be increased in 4 steps with the IT factor each step adds 0.1mm of central thickness.

Case 2: Pentacam images OD (top) and OS and (bottom) asymmetric lid aperture with scleral lens OD in situ

Fitting Tips & Considerations

When getting started with fitting specialty soft keratoconus lenses, consider focusing on one or two designs, as each design from different manufacturers has different parameters to tweak. Several factors should be considered when choosing a design to start fitting in your practice:

1. Replacement frequency: Options are available in monthly, quarterly, 6-month, and yearly replacement options.

2. Oxygen transmissibility: The thicker lens design for these specialty soft lenses results in a lower oxygen transmissibility than most regular soft lenses, with Dk/t ranging from 18 to 60 at S-3.00D.

3. Modifiable sections: Eyes with advanced keratoconus may require a lens that allows for modifying the periphery in sections, making it possible to steepen one quadrant of the lens.

4. Modifiable centre thickness: Some designs offer the option to choose the center thickness of the lens, which can be helpful when a thinner design does not fully correct the irregularity.

A fitting or trial set of the chosen design is required to determine the correct fit and power of the lens. As the lens design compensates for some or all of the irregular astigmatism, the needed spherical and cylindrical powers in the lens will be lower, sometimes significantly. Hence, an over-refraction over the trial lens is always advised. The fitting guide provides advice for the initial fitting lens based on topography, differentiating between the location of the cone, K-readings, and/or the stage of the cone.

When assessing the fit of the lens, an over-topography can provide insight into how much of the irregular astigmatism has been corrected. Taking a topography image of the eye with the lens in place and checking the Placido rings and map for irregularities can help determine the effect of the lens and whether an increase in centre-thickness may help to increase the VA or decrease the cylindrical power in the lens. This is particularly helpful when attempting to fit an advanced cone.

As mentioned earlier, these specialty soft lenses have some disadvantages that need to be considered. The increased lens thickness decreases the oxygen transmissibility. Lenses with this special design manufactured in silicone hydrogel have a maximum Dk/t at S-3.00D of 60, although the periphery is made to be thinner and therefore has a higher Dk/t. In addition, these lenses often have a replacement schedule of longer than one month, which increases the chances of infection in comparison to a monthly soft lens or a rigid lens.

Closing Remarks

In conclusion, specialty soft lenses can offer an effective alternative to rigid, hybrid and scleral lenses for patients with keratoconus. They can provide similar vision correction with greater comfort, although some disadvantages must be considered regarding oxygen transmissibility and risk of infection. Nevertheless, these lenses are another effective approach to correct keratoconic eyes and help improve vision-related quality of life for various keratoconus patients.

References

1. Jacobs, D. S., Carrasquillo, K. G., Cottrell, P. D., Fernández-Velázquez, F. J., Gil-Cazorla, R., Jalbert, I., Pucker, A. D., Riccobono, K., Robertson, D. M., Szczotka-Flynn, L., Speedwell, L., & Stapleton, F. (2021). CLEAR – Medical use of contact lenses. Contact Lens and Anterior Eye, 44(2), 289–329. https://doi.org/10.1016/j.clae.2021.02.002
   
2. Şengör, T., & Aydın Kurna, S. (2020). Update on Contact Lens Treatment of Keratoconus. Turkish Journal of Ophthalmology, 50(4), 234–244. https://doi.org/10.4274/tjo.galenos.2020.70481
   
3. Wu, Y., Tan, Q., Zhang, W., Wang, J., Yang, B., Ma, W., Wang, X., & Liu, L. (2014). Rigid gas-permeable contact lens related life quality in keratoconic patients with different grades of severity. Clinical and Experimental Optometry, 98(2), 150–154. https://doi.org/10.1111/cxo.12237
   
4. Hiraoka, T., Kiuchi, G., Hiraoka, R., & Oshika, T. (2022). Clinical performance of a custom-designed soft contact lens in patients with keratoconus and intolerance to rigid contact lenses. Japanese Journal of Ophthalmology, 66(4), 350–357. https://doi.org/10.1007/s10384-022-00924-1
   
5. Sultan, P., Dogan, C., & Iskeleli, G. (2016). A retrospective analysis of vision correction and safety in keratoconus patients wearing Toris K soft contact lenses. International Ophthalmology, 36(6), 799–805. https://doi.org/10.1007/s10792-016-0200-0

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