GP Lens Case Grand Rounds Troubleshooting Guide – 38

Advanced Keratoconus: Douglas P. Benoit, OD, FAAO

Background

Patient ML, a 38-year-old physician, presented for a complete eye examination. He had been diagnosed with keratoconus in 1989. There was a family history of keratoconus (i.e.,sister). His current GP lenses were 2 years old. He noted “light spray” and “words smearing” with his left eye lately, especially at day’s end. He had no glasses. Vision with his current contact lenses was 20/40- OD, OS, OU. An over-refraction of -0.50D improved vision to 20/30 OD, OS, OU.

Each lens had a central to inferior-central position. Movement was good with the right lens but marginal with the left lens. Fluorescein evaluation showed a trace touch centrally OU, with good mid-peripheral alignment and peripheral clearance with the right lens. The left lens exhibited adequate mid-peripheral clearance but minimal peripheral clearance. There was no superficial punctate keratopathy OU. There were inferior-central scars OU and Vogt’s striae and obvious corneal thinning observed with the right eye.

Test Procedures, Fitting/Refitting, Design & Ordering

Manifest Refraction:

OD: -6.00 -5.00 x 34 20/100
OS: -4.50 -4.50 x 131 20/100

Keratometry:

OD: 59.25@120; 63.00@030 (distorted mires)
OS: 51.50@050; 54.37@140 (distorted mires)

Corneal topography evaluation (tangential maps) showed inferior-temporal steepening OU.

Diagnostic Lenses:

Centracone (Blanchard Contact Lens), a GP lens with a spherical central, an aspheric paracentral zone and a reverse aspheric peripheral zone.

Base Curve Radius(BCR): OD: 5.30mm; OS: 6.10mm
Overall Diameter(OAD): 9.0mm OU
Periphery: STD paracentral and peripheral zones
Power: OD: -15.00D; OS: -10

The patient reported that he had good comfort with the right lens and “okay” comfort with the left lens.

Over-Refraction: Visual Acuity:

OD: -4.50DS 20/25-
OS: -2.00DS 20/30-

Both lenses exhibited central positioning. Movement with the blink was good with the right lens but excessive with the left lens. Fluorescein application revealed alignment-to-trace apical clearance with the right lens with good mid-peripheral touch and peripheral clearance. The left lens exhibited central touch and excessive paracentral touch with minimal peripheral clearance. Interestingly, a better lens-to-cornea fitting relationship was achieved on the steeper right cornea than the lesser affected left cornea. The left lens needed to be slightly steeper centrally with flatter paracentral and peripheral areas. The resultant lenses ordered were:

BCR: OD 5.30mm; OS: 6.05mm
OAD: 9.0mm OU
Periphery: OD STD paracentral and peripheral curves; OS #2 flat paracentral and peripheral curves
Power: OD -19.50D; OS -12.50D

Patient Consultation and Education

The patient understood that he would not go blind from keratoconus and that he would achieve his best vision with a GP lens. He was informed that periodic lens changes may be necessary and that he would need to be evaluated every 6-12 months. Proper cleaning techniques, including the use of a soft stem, cotton swab to clean the inside curve of the lens, were reviewed. The Boston Advance Comfort Formula solution system was dispensed, with these lenses.

Patient comfort was very good after 4-5 minutes of lens wear. His visual acuity was: OD 20/25; OS 20/30-, at distance and near. The lenses both positioned central to inferior-central with good movement in all positions of gaze. Fluorescein application revealed trace touch to slight apical clearance OU, good mid-peripheral touch OU, and good peripheral clearance OU.

Follow-Up Care/Final Outcome

At the 10 day follow-up, the patient reported good comfort with both lenses, and great vision with the right eye. The vision through his left lens was still slightly blurred but better than his previous lens.

Visual acuity: OD 20/25 with no improvement on over-refraction; OS 20/40- distance and near. A +0.50 OR improved vision to 20/30+ at all distances.

Both lenses exhibited good surface wettability and were deposit-free. The right lens positioned centrally; the left lens positioned inferiorly. The movement exhibited by both lenses was good; however, the left lens decentered more after the blink. Fluorescein application revealed the right lens to have slight apical clearance, good paracentral touch and good peripheral clearance. The left lens exhibited slight apical clearance and good paracentral touch, but the peripheral clearance was marginal. A new left lens was ordered with the following parameters:

BCR: OS: 6.05mm
OAD: 9.0mm
Periphery: OS #2 flat paracentral curve; #3 flat peripheral curve
Power: OS -12.00D

At dispensing this lens resulted in 20/30 vision at distance and near. This lens was centrally positioned with only slight inferior decentration with the blink. Movement was good in all positions of gaze. Fluorescein application revealed trace apical clearance, good touch in the paracentral area and good clearance peripherally.

Discussion/Alternative Management Options

For advanced keratoconus, specialty designs or highly customized spherical GP designs are necessary. The central corneal areas tend to be highly irregular and the apex is usually displaced. The mid-peripheral and peripheral cornea can remain surprisingly normal on topography. Corneal topography evaluation (i.e., videokeratography) is not mandatory to fit keratoconus patients but it can be quite beneficial, especially in advanced cases. It is particularly good at showing changes in the cornea over time and it can show evidence of keratoconus before keratometry and refractive changes appear. Other designs to consider would be:

Rose K 1 and Rose K 2, Soper, McGuire, etc. Standard tri-curve and tetra-curve spherical GP lenses can also be used as a starting point, with modifications dictated by careful fluorescein evaluation during the diagnostic fitting process (a must in keratoconus fits). Semi-scleral designs and scleral designs can be attempted in these cases as well. If comfort and/or fitting are a problem, piggyback lenses can be used.

For example, a hyper oxygen permeable soft lens such as Focus Night & Day (CIBAVision), is used to lessen awareness of the hyper Dk gas permeable lens placed on top to correct vision. One problem with this approach is that two care systems are typically necessary. Hybrid lenses such as the newly introduced SynergEyes (SynergEyes) help to reduce the care and handling issue, but expense and durability may be issues. There are even several soft lens designs for keratoconus, but generally vision is not as good and hypoxia can be a problem.

If tolerable lens wear or adequate vision cannot be achieved, surgery may be the only option. This is necessitated in approximately 15% of patients manifesting keratoconus. A penetrating keratoplasty (PK) has been the standard procedure for keratoconus, although modifications to the various techniques have evolved. PK will replace the irregular cornea with a more regular cornea although high astigmatism can result. This type of astigmatism is better able to be corrected and lens wear is better tolerated after the surgery.

Recently, Intacs, a semi-circular ring, has been approved for implantation into the keratoconic cornea. The idea here is to create a more normal corneal architecture and better stability of the cornea. These can make it possible to correct vision with glasses or less complex GP and soft designs.

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