Keratoconus (KC) is a progressive, localized thinning of the cornea that causes increasing irregular astigmatism resulting in distortion (1) and higher order aberrations, in particular, vertical coma (2). Consequently, visual quality with spectacles is often poor and patients rely on rigid contact lenses (CLs) to provide optical neutralisation of the irregular surface and thus be able to lead a normal life, including the ability to drive and work.
Historically, soft contact lenses (SCLs) have been considered inferior in the management of keratoconus as their tendency to drape the cornea – and therefore only minimally mask the surface irregularity – has given poorer visual performance (3). Studies have shown that RGP corneal lenses give enhanced reduction of higher order aberrations and better high and low contrast visual acuity in keratoconus than soft toric and soft spherical lenses respectively (4,5).
However, in reality visual acuity is only part of the picture and the lenses must be both tolerable and wearable where the dependency on them is so high for normal daily function. In addition, it is not always possible to achieve an acceptable or stable corneal CL fit on surfaces of such irregularity. This dilemma can be applied equally to corneal irregularity arising from corneal transplant or refractive surgery.
Modern speciality SCLs for the irregular cornea incorporate specific design features to neutralise the surface irregularity. Some rely on increased centre thickness of the lens while others employ aspheric optics. There are also design elements to refine and stabilise the lens fitting, such as independently modifiable peripheries including quadrant specific options and yet more to improve the visual quality such as front surface aberration control. As a result the way we perceive the use of SCL in the correction of the irregular cornea is changing and is making them an essential tool for contact lens practitioners.
The need for, and the possible advantages of, SCLs in the management of KC were documented by McTigue as far back as 1971. (6) In comparison to rigid CL they can represent less risk of mechanical damage to the cornea. This is particularly important as corneal scarring influences the suitability and need for other treatment options such as collagen cross linking and corneal transplantation respectively.
Initial adaptation is generally rapid with SCL and overall comfort better which can improve patient motivation to pursue contact lens fitting especially in unilateral cases. In addition, these days SCL are more familiar to patients (and practitioners) and are therefore generally less intimidating than rigid CLs. Patients presenting with KC may well have started out as soft lens wearers prior to diagnosis and so are conversant with the handling and care systems.
A further indication to consider SCL for the correction of KC is those who are experiencing ongoing problems with other lens types. This could include excessive mobility or instability that may be causing frequent displacement of a corneal CL to the extent that it may pop out of the eye. In addition, corneal lens wearers may experience glare/ flare as a result of a restrictive back optic zone diameter and/or limited wear time caused by discomfort from the lens itself or sequelae on the cornea such as 3 and 9 o’clock staining. SCLs also have the major advantage of not being susceptible to foreign bodies getting trapped behind the lens during wear and therefore may be more suitable for some environmental / occupational and recreational situations.
Disadvantages include lower DK values than modern RGP materials, handling difficulty if changing from RGP and residual inferior acuity to rigid CLs.
The fitting process can be straightforward but one must not expect it to be similar to fitting a standard soft CL. Time should be set aside to understand the patient’s requirements, discuss the options available and manage expectations. The fitting process itself requires adequate settling time and time to contemplate modifications possible and necessary on these speciality lenses that may improve the outcome for the patient. The practitioner must be familiar with methods of determining a reliable endpoint in keratoconic refraction and be able to work with a high degree of accuracy with large cylindrical elements.
There are now several specialty SCL designs available on the UK market include: Rose K2 Soft (David Thomas), Kerasoft IC (Ultravision), Novakone (SixSix Optical), Reflex Kera (No7), HydroCone (Swiss Lens), Nissel KII Soft (Cantor and Nissel).
Each lens design is different, so it is essential that the practitioner has a thorough understanding of the lens being used including fitting objectives, methods of assessment, materials and parameter range available (see Table 1).
The following case studies demonstrate some indications for SCL in the management of the irregular cornea and their outcomes.
[CaptionComponent="2191"]CASE 1
59-year-old male
[CaptionComponent="2192"]Diagnosis: left eye keratoconus
Patient presented with the following features:
• Poor tolerance of spectacles due to anisometropia
• Poor tolerance of a corneal RGP lens in the left eye
• Currently wearing a piggyback system in the left eye but was struggling with irritation after a few hours’ wear and limited visual acuity (BCVA 0.34 logMAR)
The topography plot is shown in Figure 1. The mean corneal curvature (from topography) for the left eye was 7.36mm. The fitting sequence with Rose K2 Soft lenses to the left eye is outlined in Table 2.
Final lens fitted: Rose K2 Soft
L 8.40 : 14.80 : +1.00 / -3.00 x 170 (0.00 logMAR) (see Figure 2).
Outcome: there was a significant improvement in visual acuity with the SCL in comparison to the piggyback system. The patient was ‘amazed’ by the comfort and wearability of the lens. He currently has a wear time of 12 hours per day which facilitates his lifestyle, involving a great deal of public speaking. He also much prefers the simplicity of a single lens system.
CASE 2
23-year-old male
Diagnosis: both eyes presented with keratoconus and the patient was highly atopic
Figure 3: Topography plots for case 2, right eye (3a) and left eye (3b)
[CaptionComponent="2193"][CaptionComponent="2194"]Patient presented with the following features:
• No correction worn – spectacles proved difficult to tolerate and patient felt there was no significant visual gain
• Intolerant to corneal rigid CLs which cause excessive tearing
• Worked on a building site and found corneal lenses impractical, even when worn for just a short period
• Lengthy scleral lens fitting process was still in progress due to irregular bearing zone left eye
[CaptionComponent="2195"]The topography plots are shown in Figure 3. Figure 4 shows local)ised irritation of nasal pinguecula caused by coaxial scleral lens bearing zone.
Unaided visions were R: 0.40 logMAR and L: 1.20 logMAR.
The mean simulated Ks from topography were: R: 6.7 L: 6.10
Final lenses fitted:
RE: Rose K2 Soft 8.00: 14.80: -1.50 / -1.00 x 30 (0.10 logMAR)
LE: Rose K2 Soft 7.60: 14.80: plano / -5.00 x 105 (0.30 logMAR)
Outcome: the patient did not tear at all with the SCLs and adaptation was immediate. He was extremely happy with the improvement in visual acuity and visual quality compared with that of his spectacles and is now able to wear the lenses 10 hours per day. The lenses are suitable for his working environment as there is little problem of foreign bodies lodging behind the lens. There has been no complications related to the atopic eyelids or the cornea to date.
CASE 3
29-year-old male
Diagnosis: right eye corneal graft for keratoconus, left eye early keratoconus.
Patient presented with the following features:
• Poor tolerance of spectacles due to anisometropia
• Frequent loss of corneal rigid CLs due to occupational demands requiring sustained gaze in unusual positions causing the lens to dislodge
• Longstanding neovascularisation into the superior region of the graft (Figure 5).
[CaptionComponent="2196"][CaptionComponent="2197"]Refraction:
R: +1.50 / -10.50 x 172.5 (0.20 logMAR)
L: -0.50 / -1.00 x 95 (0.00 logMAR)
Final lens fitted:
R: Kerasoft IC 8.60: 15.00: +2.00 / -7.50 x 172
Steep 2 periphery (0.10 logMAR) (see Figure 6).
Outcome: the patient was delighted with the comfort of the SCL which allowed him a wearing time of 12 hours per day, five days per week. It was appropriate for his working environment as the lens maintained adequate centration with a sufficient optic zone diameter to give good vision in all positions of gaze and with no issues of the lens dislodging. The neovascularisation has not progressed in four years whilst wearing this lens.
CASE 4
15-year-old male
Diagnosis: right eye keratoconus
Patient presented with the following features:
• Struggling to tolerate spectacle correction of rapidly increasing astigmatic correction
• Struggling to wear current rigid CL in the right eye due to excessive lacrimation and lens mobility
Refraction: RE: -0.25 / -9.50 x 30 (0.30 logMAR)
The fitting sequence with Reflex Kera for the right eye is outlined in Table 3
Final lens fitted: R Reflex Kera
7.90: 14.20: -1.00 / -6.00 x 35 (0.00 logMAR) (see Figure 7)
Outcome: the patient did not tear at all with the SCL and adaptation was rapid. The lens was stable in situ and he was able to play rugby without fear of the lens falling out.
CASE 5
68-year-old female
Diagnosis: right eye corneal grafted twice due to Fuchs’ endothelial dystrophy, phacoemulsification and toric intraocular lens (IOL).
[CaptionComponent="2199"]Patient presented with the following features:
• Unable to tolerate her spectacle correction
• Unable to achieve a stable rigid CL corneal fit
• Left eye also showing Fuchs’ endothelial dystrophy and awaiting corneal graft
Topography of the right eye revealed the irregular graft profile (see Figure 8). Unaided vision in the right eye was 1.00 logMAR.
Refraction: R: +2.50 / -9.00 x 175 (0.20 logMAR)
Final lens fitted: R: Kerasoft IC
8.60: 14.50: +4.50 / -8.00 x 180 (0.20 logMAR)
Outcome: an optimally fitting mini-scleral lens provided only limited visual acuity (0.80 logMAR). Although the anterior corneal surface irregularity was neutralised by the scleral lens liquid layer, there remained residual astigmatic error as a consequence of a poorly aligned toric IOL. At the time of fitting a toric font surface was not available for scleral lenses; therefore a specialty SCL provided the valuable solution in this case.
Conclusion
SCLs are now a viable option for the correction of mild, moderate and advanced irregular corneas and can prove particularly valuable in uniocular fittings, challenging environmental or occupational conditions, when tolerance of corneal lenses is a known issue or when a satisfactory result cannot be achieved with other lens types. In the author’s experience, modern speciality SCL designs definitely achieve more surprise than compromise.
Jennifer MacMahon is currently optometry lead at Great Western Hospitals NHS Foundation Trust. She has no financial interest in any of the products described above.
References
1 Krachmer JH, Feder RS, Belin MW. Keratconus and related non-inflammatory corneal thinning disorders. Surv Ophtlamol 1984; 28: 293-322
2 Jinabhai A, Radhakrishnan H, O’Donnell C. Higher-Order Aberrations in Keratoconus: A Review. Optometry in Practice Vol 10 (2009) 141-160
3 Jinabhai A, Radhakrishnan H, Tromans C, O'Donnell C. Visual performance and optical quality with soft lenses in keratoconus patients. Ophthalmic Physiol Opt 2012; 32: 100–116
4 Koliopoulous J, Tragakis M. Visual correction of keratoconus with soft contact lenses. Ann Ophthalmol 1981; 13: 835–837
5 Griffiths M, Zahner K, Collins M, Carney L. Masking of irregular corneal topography with contact lenses. CLAO J 1998; 24: 76–81
6 McTigue J and Townsend W. The use of a new soft lens in irregular ectatic corneas: a preliminary report. Am. Ophth. Soc., vol. 69,1971.