GP Lens Case Grand Rounds Troubleshooting Guide – 32

Subclinical Keratoconus: Phyllis Rakow, COT

Background

DD, a 47 year old female, with a history of 14+ years of soft lens wear, presented at one of our satellite offices with complaints of dryness and long-standing poor vision with soft lenses. She was wearing Preference Toric (CooperVision) quarterly replacement lenses which oriented well, but resulted in, at best, 20/30 visual acuity in each eye that did not improve with over-refraction.

Test Procedures, Fitting/Refitting, Design and Ordering (Part One)

Keratometry Readings:

OD: 48.00 @ 125/45.00 @ 035
OS: 49.75 @ 130/46.00 @ 040
(Subtle doubling of mires OS > OD)

Manifest Refraction:

OD -6.25 -1.25 X 045 20/30-2
OS -7.25 -1.00 X 130 20/30-2

Considering DD’s age at presentation, very slight mire distortion, and her history of long-term soft lens wear, contact lens-induced corneal warpage seemed a more likely diagnosis than keratoconus. DD had expressed an interest in LASIK, so pachymetry was performed.

Pachymetry:

OD: 435
OS: 450

The relatively low values all but contraindicated DD for refractive surgery and assisted in the diagnosis of keratoconus.

Slit Lamp Examination:

Negative for Fleischer’s Ring and Vogt’s Striae.

Patient Consultation and Education

The probability of mild keratoconus was discussed with DD. We explained how vision could be improved with GP lenses, but DD was resistant to the concept. She also was resistant to scheduling an appointment for an Orbscan at our main location. After much hesitation, she agreed only to the diagnostic GP fitting.

Test Procedures, Fitting/Refitting, Design and Ordering (Part Two)

A well-centered interpalpebral lens-to-cornea fitting relationship with slight apical clearance was attained with the right eye with a spherical GP lens. The left eye, however, required a Rose K lens (available from several CLMA member laboratories), which centered well, with slight feathering over the apex of the cone.

Lenses ordered based on the diagnostic fitting and over-refraction were:

ODOS

Base Curve Radius (BCR): 7.40mm 7.20mm
Power: -7.25D -7.50D
Overall/Optical Zone Diameter (OAD/OZD): 9.0mm 9.0mm
Secondary Curve Radius/width (SCR/W): 8.60/.3mm STD
Peripheral Curve Radius/width (PCR/W): 10.50/.3 mm STD
Material: Boston ES Boston ES
Design: Standard with Rose K + Lenticular

Follow-Up Care/Final Outcome

DD was extremely apprehensive about initiating wear of GP lenses. The lenses were inserted and visual acuity checked after 30 minutes of adaptation, when her initial adaptation symptoms had subsided.

Visual Acuity:

OD 20/20-2
OS 20/20-2

DD was amazed at the crispness of her vision. She was instructed on lens insertion and removal and given the Boston Advance Cleaner, Boston Original Conditioner, and Boston Rewetting Drops (Polymer Technology Corporation). She was placed on an accelerated wearing schedule, since she was a well-adapted soft lens wearer and had been wearing relatively low oxygen permeability toric lenses.

We took the opportunity at the dispensing visit to make DD aware of the National Keratoconus Foundation and gave her a copy of their publication, “What is Keratoconus?” and their latest newsletter. We urged her to contact the Foundation, access their website (www.nkcf.org), and subscribe to their newsletter.

DD adapted quickly to her GP lenses, as she was highly motivated by the dramatic increase in her visual acuity. At her follow-up visits, her lenses exhibited excellent centration OU, with near-alignment OD and slight feather touch over the cone OS. She was still complaining of dryness; therefore, the ophthalmologist prescribed Restasis, followed at a subsequent visit by the insertion of punctal plugs OU. This significantly improved her comfort.

Discussion/Alternative Management Options

Although most patients with keratoconus are diagnosed at an earlier age, DD’s condition was not diagnosed until her initial visit to our office at the age of 47. As we have observed inferior corneal ectasia and subtly irregular mires in many soft toric lens wearers, we did not suspect keratoconus until after pachymetry was performed. The condition had most probably existed for many years, but the etiology of her reduced vision with glasses and soft toric lenses had never been pursued. Her refusal to travel to our main location for an Orbscan has limited our base line data, but we do not anticipate much, if any progression at her age.

If DD had been totally resistant to trying GP lenses, we could have attempted to fit her with one of the soft cone lenses or left her in toric soft lenses, but she probably would not have been able to achieve the crisp visual acuity that the GP lenses provided. We have found that once patients with irregular astigmatism discover how well they can see with a rigid modality, they rarely hesitate to proceed with the fitting. We instill topical anesthetic eye drops whenever necessary if the patient is very sensitive or very apprehensive.

Keratoconus fitting is greatly simplified if one or more diagnostic sets of lenses are kept in the office. Our practice is fortunate in having a large and very active corneal service, and we have numerous diagnostic sets for keratoconus in a variety of base curve radii and diameters. The ability to select the optimum base curve radius and diameter, and to obtain the optimum power by over-refracting at the initial visit saves chair time, staff time ordering, returning, and reordering patient lenses, mailing fees, phone calls to set up appointments each time the lens parameters are changed, and the patients’ time. Most important, it maintains patient confidence, since the lenses do not have to be exchanged numerous times until a satisfactory fit is attained.

We have had much success with the Rose K lens, available from Blanchard Contact Lens, as well as nipple cone keratoconus lenses from Lens Dynamics. Other designs include the Ni-Cone lens (Lancaster Contact Lens); Soper-cone and McGuire lenses, available from many CLMA member laboratories; and proprietary keratoconus designs from individual GP laboratories.

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