Bitoric rigid gas permeable contact lens fitting for the management of a corneal scar caused by herpes zoster ophthalmicus

Authors


Mrs Victoria de Juan, IOBA Eye Institute, University of Valladolid, Paseo de Belén, 17, 47011, Valladolid, SPAIN. E-mail: victoria@ioba.med.uva.es

Abstract

Empirical fitting of a bitoric rigid gas permeable contact lens for the management of a scarred irregular cornea caused by herpes zoster ophthalmicus is described. Two corneal scars, which affect the pupil axis, caused an irregular cornea and produced low visual acuity and anisometropia. Two contact lenses were necessary to complete the fitting. Visual acuity improved from 0.2 to 1.0. The rigid gas permeable lenses can be a good alternative in the management of patients with irregular corneas caused by herpes zoster ophthalmicus.

Corneal scarring following herpes zoster ophthalmicus (HZO) can frequently cause a significant reduction of vision due to corneal leukomas and irregular astigmatism.1 Small peripheral scars might not affect visual quality, but large mid-peripheral scars can cause severe astigmatism. Many of these patients require photorefractive keratectomy,1 keratoprosthesis2 or keratoplasty1 for recovery of visual acuity. Rigid gas-permeable (RGP) contact lenses can mask significant amounts of irregular astigmatism and can improve visual acuity in some of these patients.3,4

This paper presents a case in which bitoric RGP contact lenses were prescribed to improve the vision of a patient with corneal leukomas and irregular astigmatism secondary to herpes zoster keratitis.

CASE REPORT

A 62-year-old male patient was referred for a contact lens fitting. The patient had been diagnosed with herpes zoster ophthalmicus five years earlier. Painful cutaneous lesions appeared on the right side of his face and these were associated with blurring and severe ocular pain in the right eye. The patient did not wear glasses or contact lenses. His ocular history revealed no other notable findings. He did not have a significant familial ocular history. His general health was excellent and he was not taking any medication on a regular basis.

The uncorrected visual acuities were 0.2 in the right eye and 1.2 in the left eye. Visual acuity in the right eye was 0.6 with a subjective refraction of plano/-4.00 × 175°. Slitlamp examination of the right eye showed two corneal scars in the mid-periphery, involving the pupil axis, at one and six o'clock, respectively (Figure 1A). The left eye was normal.

Figure 1.

A. Slitlamp examination showed two corneal scars along the vertical axis. One of the scars affects the pupil axis. B. Ring segments of the topographical image of the described case. C. The fluorescein pattern with the toric rigid gas-permeable lens shows the central alignment and two apical clearances in the scar zone. D. Orbscan elevation topography shows an irregular corneal surface with high astigmatism (anterior elevation as the best fitting surface).

Modifications of the corneal curvature and pachymetry were caused by these scars along the vertical axis (Figures 2A and 2B), producing corneal astigmatism (Figures 2C and 2D).

Figure 2.

A. Detail of the upper scar. B. Alteration of the corneal surface as shown by optical section. C. Orbscan keratometric map shows high astigmatism with a regular pattern. D. Keratographic keratometric map gives good agreement with the Orbscan keratometric map.

Orbscan II (Bausch & Lomb, Inc, Rochester, NY, USA) revealed an irregular cornea with astigmatism of 13.8 D. The Orbscan-simulated keratometric readings were 43.6 D (7.74 mm) @ 170°× 57.8 D (5.84 mm) @ 80°. Manual keratometry (Ophthalmometer OM-1, Topcon, Japan) was 40.91 D (8.25 mm) @ 180°× 44.41 D (7.60 mm) @ 90°.

Keratographic topography (Oculus Optikgeräte GmbH, Wetzlar, Germany) showed high astigmatism of 10 D. The keratograph-simulated keratometry readings were 44.00 D (7.67 mm) @ 160°× 54.00 D (6.25 mm) @ 70°. The ring segments of the topographical image were distorted (Figure 1B).

A bitoric RGP contact lens was proposed to improve visual acuity in the right eye. An empirical fitting was provided. After the trial fitting of two diagnostic contact lenses in the same visit (Table 1, Figure 3), the definitive contact lens was calculated with a back optic zone radius of 7.70/7.35 mm, total diameter 9.60 mm, power +1.50 D and Boston ES (BIAS-MAC lens design of Hecht Contactlinsen/Conoptica, Barcelona, Spain). The examination revealed good centration, movement and tear exchange. The fluorescein pattern (Figure 1C) showed good central alignment with two paracentral clearances in the two scar zones (vertical meridian), mild peripheral alignment with optimal clearance under the peripheral curve and good edge clearance to facilitate tear exchange. This fluorescein pattern was consistent with the Orbscan anterior surface elevation map (Figure 1D).

Table 1. Trial contact lens parameters used to calculate the definitive contact lens
Trial lensBOZR (mm)Diameter (mm)Power (D)Geometry/ModelOver refractionVAComment
  1. Material for all diagnostic lenses: Boston ES, Hecht Contactlinsen/Conoptica, Barcelona, Spain.

  2. BOZR: back optic zone radius; VA: visual acuity with over correction in trail frame

17.709.60-3.00Aspheric/BIAS S+4.500.8Visual fluctuation
27.70/7.359.60-3.00Bitoric/BIAS MAC+4.501.0Good alignment
Figure 3.

A. The fluorescein pattern with the first trial lens. The sloping corneal surface causes excessive movement and edge lift in the vertical meridian. B. The fluorescein pattern with the second trial lens shows good alignment.

At the three-month after-care visit, the patient indicated that he was wearing the lens approximately eight hours per day, six to seven days per week without discomfort. No visual acuity changes were found. Slitlamp examination did not reveal corneal or conjunctival staining or any other ocular complications associated with contact lens wear.

DISCUSSION

Contact lens fitting might be required after herpes zoster ophthalmicus for optical reasons, such as the correction of irregular astigmatism, high regular astigmatism, anisometropia and secondary aniseikonia, as well as ametropia, and in cases where the patient wants to wear contact lenses in preference to spectacles. In the present case, the contact lenses were fitted to improve visual acuity and maintain some degree of binocular function. Additionally, the lenses permitted the resumption of some leisure activities, such as shooting and hunting.

The RGP contact lenses essentially create a new spherical refraction surface, which allows the tear film beneath the contact lens to neutralise the corneal astigmatism. In many cases, an irregular cornea can be fitted with spherical or aspheric RGP designs. Although spherical designs often fail due to poor fitting, specialty lens designs might provide a stable, comfortable lens that offers visual improvement.5 Back surface toric and bitoric designs are most useful when the corneal topography consists of large amounts of astigmatism. A spherical back surface has difficulty centring on the eye and the sloping corneal surface causes excessive movement and edge lift in the vertical meridian. This excessive movement results in discomfort and visual fluctuations (Table 1). For this reason, a bitoric contact lens was fitted to lessen the edge lift in the vertical meridian and decrease movement. In this type of lens, the anterior surface has two different radii to compensate for the residual astigmatism. This residual astigmatism is created by the lack of parallelism between the corneal astigmatism and the back surface of the contact lens. It may also be caused by the difference between the refractive index of the lens material and the tears. The final refractive effect is spherical and this is called a compensated bitoric lens. The back toric surface corrects the refractive cylinder created by the corneal toricity and the front surface incorporates the correction for the induced astigmatism.6 The lens is called BIAS MAC and will always have two back meridians with a constant difference of 0.35 mm. The practitioner chooses the flattest back radius of the contact lens according to the flattest meridian of the cornea and the other back radius is selected by the manufacturer (0.35 mm steeper).

In irregular corneas, traditional fitting nomograms might not be appropriate. Therefore, computerised corneal topography has been invaluable in assisting the practitioner to select the most appropriate RGP lens design. The quality of the captured image is a crucial factor for accurate topographic results.7

In this case, empirical fitting was proposed, aiming for the proper fluorescein image with a contact lens and corneal alignment.3 This type of fitting might be challenging and time consuming, although specialty lens designs (for example, toric and reverse-geometry) could take less fitting time than standard or aspheric RGP lenses due to better centration and stabilisation.8 For these reasons, these contact lenses have been proposed after corneal graft surgery9 or following laser refractive surgery.8 In the patient in the present study, a bitoric compensated RGP contact lens was fitted after only two diagnostic lenses and we obtained good centration with no superior dislocation (Figure 1C).

Visual acuity with RGP contact lens was significantly improved (from 0.2 to 1.0) because the tear film underneath the contact lens neutralises the corneal surface irregularities, similar to previous reports.4 The visual acuity with the contact lens (1.0 in the right eye) was similar to the previous visual acuity (subject not wearing glasses before herpes zoster ophthalmicus). Visual acuity could be similar in both eyes (left eye visual acuity was 1.2).

Acceptance of the contact lens was high with approximately eight hours per day of wear; however, some authors conclude that the long-term success for these patients wearing contact lenses is poor.10 An alternative to contact lens fitting for optimal visual gain is eye surgery with different techniques (for example, keratoplasty, topographic-linked corneal excimer laser ablation and wave-front guided aberration-controlled laser-assisted in situ keratomileusis). Eye surgery is difficult and of limited use in cases of very high astigmatism and insufficient corneal thickness, and limited by the availability of donor tissue, the difficulty of the technique and post-operative complications. Contact lenses are the first choice and sometimes the best solution for optical rehabilitation in eyes with irregular corneal surfaces.3

CONCLUSION

The fitting of contact lenses in a patient who has corneal scars caused by herpes zoster ophthalmicus is generally difficult. Toric geometry contact lens fitting can be a good alternative in these cases. Analysis of fluorescein patterns could be useful when fitting RGP contact lenses and could take less time and fewer visits than standard or aspheric RGP contact lenses in these patients.

Ancillary