GP Lens Case Grand Rounds Troubleshooting Guide – 05

Corneal Desiccation: Ed Bennett, OD, MSEd

Background

Patient AM, a 25 year old graduate student, came to the clinic complaining of gradual increase in dryness and redness, resulting in an inability to wear the lenses all day. Her friends have also been commenting that her eyes look red. She also indicated that her vision tended to be blurred with the lenses when she is driving at night. She has been wearing a medium Dk silicone/acrylate lens material for the past 11 years.

Test Procedures, Fitting/Refitting, Design and Ordering

Evaluation of Current Lenses:

Visual Acuity (with Contact Lenses):

OD: 20/20-1 (fluctuates with blink)
OS: 20/20-2 (fluctuates with blink)

Over-Refraction:

OD: +0.25DS 20/20-1
OS: +0.50 -0.25 x 171 20/20

Slit Lamp Examination (with Contact Lenses):

Both lenses decentered inferiorly and are not picked up adequately with the blink. Excessive edge clearance is present 360˚ OU. Some muco-protein filming was evident after the blink OU.

Evaluation Without Lenses:

Slit Lamp Examination (After Lens Removal):

OD: Grade 2+ corneal desiccation temporally and Grade 2 nasally.
OS: Grade 2 corneal desiccation nasally and temporally.

Grade 2 bulbar conjunctival injection OU and Grade 1 papillary hypertrophy of the superior palpebral conjunctiva OU.

Tear Break-Up-Time was 8 seconds OD and 7 seconds OS.

Manifest Refraction:

OD: -5.75 -1.50 x 178 20/20+2
OS: -5.25 -1.75 x 005 20/20+1

Keratometry:

OD: 43.25@180;44.50@090 (mires clear)
OS: 43.50@180;45.00@090 (mires clear)

Anatomical Measurements:

Pupil Diameter (photopic): 6mm
Horizontal Visible Iris Diameter: 12mm
Upper Lid Position: Overlaps superior limbus by approx. 1mm
Vertical Fissure Size: 10.5mm

Her Lenses Verified as:

ODOS

BCR: 7.85mm 7.85mm
OAD/OZD: 9.2/7.6mm 9.2/7.6mm
Power: -5.00D -5.00DS
SCW: .3mm .3mm
PCW: .5mm .5mm
Center Thickness: .15mm .15mm
Edge Thickness: .23mm .24mm

Lens Design and Ordering:

As a result of the inferior decentration of these lenses, an ultrathin lens design was empirically ordered. In addition, the overall diameter was increased to 9.6mm and the optical zone diameter was increased to 8.2mm as a result of her symptoms of glare at night. Although the peripheral curve radii were unknown, the presence of excessive edge clearance accompanied by a relatively large peripheral curve width resulted in designing the lens in a tetracurve design with a narrower bevel width. The edge thickness was excessive and the new lenses were ordered with a plus lenticular.

The following lenses were ordered:

ODOS

BCR: 7.81mm 7.76mm
OAD/OZD: 9.6/8.2mm 9.6/8.2mm
Power: -5.00D -5.00DS
SCR/W: 8.6/.2mm 8.6/.2mm
ICR/W: 9.6/.2mm 9.6/.2mm
PCR/W: 11.0/.3mm 11.0/.3mm
Center Thickness: .11mm .11mm
Edge: .Plus Lenticular

Patient Consultation & Education

Upon dispensing of the lenses, AM was satisfied with both comfort and vision.

Visual Acuity:

OD: 20/20 +2
OS: 20/15 -2

Over-Refraction:

OD: Pl -0.25 x 173 20/20 +2
OS: +0.25 DS 20/15 -2

Slit Lamp Examination:

Both lenses exhibited good centration and a lid attachment fitting relationship. The right lens decentered slightly nasally but exhibited good papillary coverage. The fluorescein pattern of both lenses exhibited slightly greater clearance inferiorly than laterally as a result of the mild with-the-rule astigmatism; however, overall, adequate edge clearance was present which was much less than with her previous lenses.

AM was provided with a combination wetting/soaking (i.e., conditioning) solution accompanied by an abrasive daily cleaner to be used immediately upon lens removal at night and a liquid enzyme cleaner to be used once a week. She was also taught a new method of lens removal as a result of the lower edge clearance of the new lenses. The traditional method of using one finger at the lateral canthus and pulling temporally is often ineffective in dislodging larger, lower edge clearance designs which also tend to move less on the eye with the blink. She was instructed to use the middle finger of the opposite hand (as eye) to pin the upper lid against the eye and the middle finger of the same hand (as eye) to pin the lower lid against the eye. She was then instructed to pull the lids laterally and blink.

Follow-Up Care/Final Outcome

At the one week follow-up visit, the patient was quite satisfied with the comfort and vision of her lenses. The following testing was performed:

Visual Acuity:

OD: 20/15 -2
OS: 20/15 -2

Over-Refraction (Spherical):

OD: Pl 20/20 +2
OS: +0.25 DS 20/25 -2

Slit Lamp Examination:

Both lenses exhibited good centration and a lid attachment fitting relationship similar to the dispensing visit. Upon lens removal the corneal desiccation was unchanged from the dispensing visit but the injection was reduced to Grade 1.

At the three month follow-up visit, AM was quite satisfied with her lenses. The vision and slit lamp findings were similar to the one week visit with the exception that the corneal desiccation was reduced to very mild diffuse (Grade 1) staining and no injection was present. The patient was dismissed until his annual examination.

Discussion/Alternative Management Options

The incidence of corneal desiccation has been reported to occur with 40-90% of GP lens wearers. (1,2) It has been classified as moderate-to-severe in about 15% of cases.(3,4) Many causes have been proposed but if normal blinking is compromised (i.e., defective or thick edge, high edge clearance) or if the patient has poor tear quality (i.e., less than 10 second tear break-up-time),desiccation is more likely to result. In addition, it is evident that inferior decentering lenses are much more likely to result in desiccation than intrapalpebral and superior fitting lenses.(5) This is, in part related to the increase in superior edge clearance resulting from an inferiorly displaced lens.

If the patient is moderately or highly myopic, such as in this case, the use of an ultrathin design reduces the lens mass significantly increasing the likelihood that the lens will position more superiorly. Likewise, the use of a lenticular (or similar) edge design, when indicated, will assist in centration as well. Typically, a plus lenticular edge design — resulting in a thinner edge, and therefore less edge contact — will be necessary in high minus lens designs (i.e., ≥ -5.00D) and plus lenticular designs — resulting in a thicker edge, increasing the likelihood the lens will be picked up superiorly — is indicated for all plus and low (≤ -1.50D) lens powers.(6) Finally, excessive edge clearance is present — denoted by a thick band of peripheral pooling — the use of steeper and narrower peripheral curve radii — will reduce edge clearance, possibly resulting in less funneling of the peripheral tears underneath the edge as well as less contact of the upper lid with the edge of the lens. Increasing overall lens diameter has also been found to be beneficial due to providing more corneal coverage and reducing the area that would be prone to desiccation.(7)

An alternative plan would have been to refit this patient into a soft toric lens. However, as she has been accustomed to the vision provided by a GP lens this option would be less desirable than making an effort to improve centration and, therefore, hopefully reduce and even eliminate the symptoms and clinical signs of dryness. One of the common errors made today is refitting the symptomatic and even the asymptomatic GP wearer into soft lenses. Often the result is a patient who is not as pleased with the quality of their vision.

References

1) Edrington TB, Barr JT. Peripheral corneal desiccation. Contact Lens Spectrum 2002; 17:46.

2) Bennett ES. Lens design and trouble shooting. In Bennett ES, Grohe RM, eds. Rigid Gas Permeable Contact Lenses. New York, Professional Press, 1986:189-224.

3) Henry VA, Bennett ES, Sevigny J. Rigid extended wear problem solving. Int Contact Lens Clin 1990;17:121-133.

4) Fonn D, Sorbara L. Rigid gas permeable lens problem-solving. In Bennett ES, Weissman BA: Clinical Contact Lens Practice (2nd ed.), Philadelphia, Lippincott Williams & Wilkins, 2005:341-354.

5) Henry VA, Bennett ES, Forrest JF. Clinical investigation of the Paraperm EW rigid gas-permeable contact lens. Am J Optom Physiol Opt 1987;64:313-320.

6) Bennett ES. Rigid gas-permeable lens problem-solving. In Bennett ES, Henry VA: Clinical Manual of Contact Lenses (2nd ed.) Philadelphia, Lippincott Williams & Wilkins, 2000:181-220.

7) Schnider CM, Terry RL, Holder BA. Effect of lens design on peripheral corneal desiccation. J Am Optom Assoc 1997;68:163-170.

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