Contact Lens Correction of a
Herpes Simplex-Damaged Cornea
BY TERRY SCHEID, O.D., F.A.A.O.; LEONID ABRAMOV, O.D.;
& MICHAEL GEORGESCU, O.D.
Despite some potential risks, there are times when prescribing a rigid gas permeable lens for a herpes-damaged cornea is a viable treatment option.Rigid gas permeable lens therapy for a patient after resolved stromal herpetic keratitis and induced irregular astigmatism presented a unique challenge. Here we describe the pathology and fitting considerations that led to our decision to pursue this treatment plan despite some potential risks.
The patient, a 48-year-old tractor trailer driver with a 20-year history of herpes simplex keratitis, was having difficulty driving due to blurred left eye vision and halos, especially in dim light. He was unable to wear spectacles due to anisometropia complications and best left eye acuity of 20/200. He was referred to us for a contact lens evaluation.
THE INITIAL VISIT
Uncorrected distance visual acuity was: OD 20/20; OS 20/400 ph20/200. Uncorrected near visual acuity was: OD 20/80; OS 20/200 @ 16 in. Corrected distance visual acuity was: OD +0.50 -0.25 x 35 20/20; OS +0.75 -4.50 x 100 20/200; +1.75 add 20/20 @ 16 in. OU.
Slit lamp examination revealed mild blepharitis in both eyes. The right cornea and conjunctiva were clear and quiet with a grade 4 angle. The left cornea revealed deep stromal scarring and approximately five millimeters superior neovascularization (Fig. 1). The anterior chamber angle was grade 4.
Corneal topography revealed left eye corneal curvature of 51.35 @ 50/47.42 @ 150 and irregular astigmatism with the steepest area corresponding to the stromal scarring areas (Fig. 2). Conventional keratometry gave a measurement of OS 44.50 @ 140/49.75 @ 50, slightly irregular and distorted. Applanation tonometry was 16mm Hg. OD and 14mm Hg. OS.
Herpetic corneal scarring and neovascularization led to astigmatism and poor spectacle corrected acuity of the left eye.
EXPLORING THE OPTIONS
Due to the astigmatism and the presence of active neovascular vessels, a rigid lens was deemed more appropriate than a soft lens. After observing several diagnostic rigid lenses of various designs and materials, we obtained the best initial fit with the Envision design by Polymer Technology. This biaspheric design, made of Boston RXD material (45 Dk), has a 7.0mm, low eccentricity optic area with a hyperbolic eccentricity peripheral curve, specific gravity of 1.27, available base curves of 7.3 to 8.3 (in 0.1mm increments) and diameters from 9.3 to 10.3mm. According to the literature, this lens has been used successfully with astigmatic, irregular and post-keratoplasty corneas.
A base curve of 7.4mm, total diameter of 9.6mm, center thickness of 0.16mm, and total power of -1.50D resulted in 20/20 distance visual acuity, good vertical and horizontal corneal positioning, and a mild apical touch, with-the-rule pattern (Fig. 3).
The patient adapted well to this design. We changed the base curve to 7.3mm to move the center of gravity of the lens posteriorly to stabilize movement, but the patient still lost several lenses while glancing quickly to the side. He also stated that the lens displaced inferiorly at times. A drawback to the Boston RXD material is the high specific gravity (1.27) creating more lens mass for some designs. Other options were to increase the lens diameter and/or lenticularize the lens to decrease center thickness. [Author's Note: The Boston Envision is now available in the Boston 7 material (Dk 73) with base curves from 7.0 to 8.3mm in 0.1mm steps. This material may also have proved helpful in this case.]
We decided to try a Fluorocon design (FluoroPerm 60 material) from Paragon Vision Sciences. This lens has a specific gravity of 1.15, a Dk of 60 and minus lenticular design with powers of -3.00D and less. We dispensed a lens with the following parameters: 7.30mm base curve; 9.5mm T.D.; -1.50D; 8.4mm o.z.; 9.1/0.35mm wide secondary curve; third curve of 10.5/0.2mm width; and 0.12mm center thickness. The lens positioned well and stabilized due to the thinner design and lower specific gravity. The cornea has remained stable for the past seven months. Contact lens corrected distance visual acuity remains at 20/20 and a +1.75D reading prescription for each eye gave 20.20 @ 16 in.
ETIOLOGY OF HERPES SIMPLEX KERATITIS
Herpes simplex is the most common cause of corneal blindness in developed countries. In the United States, 70 percent of the population have been infected by age 25, and 97 percent have been infected by age 60. Initial infection is subclinical in 85 percent to 99 percent of cases and one percent of cases progress to severe acute illness.
The infection of herpes simplex is subdivided into primary, latent and recurrent findings. Ocular manifestations of primary infection are: follicular conjunctivitis with pre-auricular lymphadenopathy and malaise, usually unilateral presentation, and pseudomembranes in 50 percent of severe cases. Vesicular or ulcerative keratitis may occur. Corneal involvement may include diffuse superficial punctate keratitis, focal epithelial lesions and pathognomonic dendrites. The lid margins may exhibit lesions similar to staph ulcerative blepharitis. Loss of corneal sensitivity may occur. The margins of an untreated dendrite may expand to a broader lesion, termed a geographic ulcer.
Herpes simplex virus (HSV) causes recurrent infections by staying latent in the trigeminal ganglia. Recurrent HSV may be caused by fever, sun exposure, stress, menstruation, trauma and epinephrine topical ocular drops. Trauma could include wearing contact lenses.
Stromal keratitis can be caused by incomplete viral particles and proteins acting as antigens and promoting inflammatory responses that are immune mediated. Disciform keratitis involves stromal cell infiltration and edema in an oval pattern. Necrotizing or ulcerative keratitis may have a stromal and necrotic cheesy white infiltrate. The term HSV interstitial keratitis implies vascularization, infiltration and thinning. Differential diagnosis involves ruling out acanthamoeba, bacterial or fungal infections.
Traditionally, treatment of herpetic keratitis involves the use of antivirals, cycloplegics and possibly corticosteroids to control the inflammatory response with stromal involvement. The antiviral treatment of choice is trifluridine (Viroptic), with idoxuridine, vidarabine ointment and oral acyclovir being adjuncts or alternatives. Oral treatment with acyclovir may effectively reduce the healing time of epithelial dendritic ulcers, although the effect on stromal disease varies.
VISUAL REHABILITATION AFTER CORNEAL DISEASE
Visual rehabilitation for irregular astigmatism associated with corneal disease can be very successful. In this case, the possibility of reactivation of the herpes virus remains. Because of the vascularized cornea, mid to high Dk RGP materials were in order. The FluoroPerm 60 material with the center thickness of 0.12mm gives a Dk/L (oxygen transmissibility) of approximately 50 x 10-9 (cm/sec) (ml 02/ml mm Hg.). The minimal center thickness and moderate specific gravity may result in less mechanical pressure to the cornea.
To avoid removal irritation, we advised the patient to use rewetting drops and a suction cup for lens removal. We educated him in the proper use of cleaning, disinfecting and inserting solutions. Enzyme cleaning of the material and regular lens replacement were advocated. After careful evaluation, we concluded that rigid lenses would so substantially improve this patient's visual acuity and his quality of life, and solve his occupational problems, that they warranted the risk. We have advised him of reactivation warning signs and symptoms and we will monitor him carefully. CLS
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