GP Lens Case Grand Rounds Troubleshooting Guide – 33

Intermediate Keratoconus: Susan Resnick, OD

Background

MS is a 23-year-old black male who was diagnosed with keratoconus 18 months prior to his initial visit. He had never worn glasses or contact lenses.

Test Procedures/Fitting/Design and Ordering

Corneal topography confirmed the diagnosis of keratoconus, indicating nipple type cones. The cone in the right eye was more advanced, but centered. The cone in the left eye was slightly temporal. Slit lamp examination was positive for Vogt’s Striae OD only. There was no scarring in either eye and only very slight corneal thinning was detected (OD > OS). Scissors reflex was present bilaterally.

Manifest Refraction:

OD: +1.50 -10.00 x 095 20/400
OS: +2.00 -8.00 x 115 20/60

Sim K Readings:

OD: 57.25 @ 100/48.75 @ 010
OS: 47.62 @ 068/43.25 @ 158

Lens Design and Diagnostic Fitting

Rose K Boston ES diagnostic lenses (selected from available lenses in the author’s fitting set) were inserted with the use of topical anesthetic. The parameters were:

ODOS

Base Curve Radius (BCR) 6.30mm 7.00mm
Power -6.75D -4.25D
Overall Diameter (OAD) 8.15mm 8.30mm
Peripheral Curve Radii: Standard Standard

Over-Refraction:

OD: -6.50DS 20/30
OS: -2.50DS 20/20

Slit Lamp Evaluation:

The fluorescein patterns (viewed with a Wratten filter using high illumination and low magnification) revealed minimal apical clearance OD with slightly excessive inferior edge clearance and a slightly excessive central apical clearance pattern OS with intermediate seal-off. As the patient was presently without any form of visual correction, the following temporary (satisfactory fitting) lenses were dispensed to him from inventory:

ODOS

Base Curve Radius (BCR) 6.40mm 7.20mm
Power -11.50D -5.75D
Overall Diameter (OAD) 8.50mm 8.70mm
Peripheral Curve Radii: Standard (Rose K) Standard

Visual Acuity (with Temporary Lenses):

OD: 20/40 Over-Refraction: -1.00DS 20/25
OS: 20/20 Over-Refraction: Plano 20/20

Both of these temporary lenses exhibited slight central touch with slightly excessive inferior lift, but the patient reported acceptable comfort and vision. The following final lens design was ordered:

ODOS

Base Curve Radius (BCR) 6.30mm 7.10mm
Power -13.00D -6.25D
Overall Diameter (OAD) 8.00mm 8.30mm
Peripheral Curve Radii: Standard (Rose K2) Standard (Rose K2)
Material: Boston XO Boston XO

Patient Education/Consultation

The patient was given a wearing schedule of four hours on day one, increasing wear by two hours per day to ten hours until rechecked. He was instructed on insertion, removal, and lens care as well as lens recentering. Wrap around type sunglasses were recommended to reduce glare, tearing, and foreign bodies. The patient was also educated about the progressive nature of his condition and the need for rigorous follow-up and monitoring.

Follow-Up Care/Final Outcome

The patient returned for final dispensing one week later. He had achieved a wearing time of ten hours. He was checked first with the temporary lenses. There was no change in visual acuity, over-refraction and lens-to-cornea fitting relationship. The slit lamp examination was negative for any significant staining.

The patient inserted the final lenses and they were allowed to settle for ten minutes. The visual acuity was OD 20/25 OS 20/20 with plano OR OU. Both lenses exhibited good centration, minimal apical clearance and acceptable peripheral clearance with fluorescein application. There was good tear exchange with .5mm to 1.0mm movement with the blink.

Discussion/Alternative Management Options

When possible, this author prefers a minimal apical clearance fitting strategy to minimize the potential for scarring or insult to the fragile epithelial overlying the cone. (Note: the recommended fitting of Rose K lenses is to achieve slight central touch.) The least amount of movement, which still permits adequate tear exchange, has proven to this author to provide the best comfort and quickest adaptation, especially for new wearers.

The lens used here is a new version of the Rose K which controls for aberration and provides a larger posterior optical zone diameter. This reduces flare and glare. The original Rose K fitting set is used to fit Rose K2 lenses. Alternative designs for intermediate keratoconus include the CLEK lens design and the McGuire Lens, among others.

A good practice strategy is to have a fitting set on hand for at least one design. As the keratoconus progresses, smaller overall diameters (as well posterior optical zone diameters) are required for better alignment and a three-point touch fit may become more realistic.

Supplemental Readings

  1. Bennett ES, Cutler S. Keratoconus. In Bennett ES, Hom MM. Manual of Gas Permeable Contact Lenses (2nd ed.). Elsevier Science, St. Louis MO, 2004:223-271.
  2. Bennett ES, Barr JT. Keratoconus. In Bennett ES, Henry VA. Clinical Manual of Contact Lenses (2nd ed.) Lippincott Williams & Wilkins, Philadelphia, PA, 2000:493-530.
  3. Zadnik K, Barr JT Diagnosis, Contact Lens Prescribing, and Care of the Keratoconic Patient, Butterworth-Heinemann,Woburn MA, 1999.

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