GP Lens Case Grand Rounds Troubleshooting Guide

Inferior Decentration (Hyperope): Douglas P. Benoit, OD, FAAO

Background

Patient CT presented for contact lens consultation. This 33-year-old chef had been wearing corneal GP lenses for several years and was finding the latest pair (about 4 months old) to be uncomfortable after 6-7 hours of wear. The lenses had been fit by another practitioner after one lens had been lost. After dispensing, no follow-up visit was scheduled.

Visual Acuities (with Contact Lenses):

OD: 20/25
OS: 20/25

Over-Refraction:

OD: Plano DS 20/25
OS: -0.25 DS 20/20-

Slit Lamp Evaluation (with Contact Lenses):

Both lenses had a slightly inferior position in primary gaze. Both lenses moved excessively and only briefly interacted with the lids on blinking. Fluorescein evaluation showed slight apical bearing OU, with slightly excessive mid-peripheral and peripheral clearance OU.

Slit Lamp Evaluation (without Contact Lenses):

Each cornea had mild, central superficial punctate keratitis (SPK), with the right cornea slightly worse than the left. The remainder of the external ocular health was normal.

Current Lens Parameters:

Test Procedures, Fitting/Refitting, Design and Ordering

Manifest Refraction:

OD: +3.50 -1.25 x 165 20/25-
OS: +3.00 -1.00 x 023 20/20-

Keratometry:

OD: 42.00 @ 170; 43.50 @ 080 (slight mire distortion)
OS: 42.25 @ 010; 43.50 @ 100 (slight mire distortion)

Anatomical Measurements:

Pupil Diameter (room illumination): 4.5mm
Upper Lid Position: Overlaps superior limbus by approx. 2mm
Lower Lid Position: Tangent to lower limbus
Vertical Fissure Size: 11.5mm

Diagnostic Lenses:

 
After 5 minutes of settling, comfort was very good OU.

Visual Acuities (with Contact Lenses):

OD: 20/25
OS: 20/25

Over-Refraction:

OD: +1.00DS 20/25
OS: +0.75DS 20/20-

Slit Lamp Evaluation (with Contact Lenses):

Each lens positioned superior central with lid attachment. Movement was good in all positions of gaze. The fluorescein pattern showed slight apical clearance OD and alignment OS. There was good mid-peripheral and peripheral clearance OU. The OD lens base curve radius needed to be 0.25mm flatter and the lenses ordered were as follows:

Patient Consultation and Education

The need to change the lenses’ fit in order to obtain good comfort was discussed with the patient. The issues of lens thickness, lens diameter, and the base curve-to-cornea fitting relationship were presented in lay terms, which the patient appreciated. The patient was advised to wear her glasses until the new lenses arrived in order to allow the SPK to resolve. The lenses were ordered and a dispensing visit scheduled for one week. At dispensing the lenses were allowed to settle for 5-10 minutes. They had been cleaned and soaked after arriving from the laboratory and being verified/inspected.

Visual Acuities (with Contact Lenses):

OD: 20/20
OS: 20/20

Slit Lamp Evaluation (with Contact Lenses):

Each lens exhibited a superior central position with slight lid attachment. Movement was good in all positions of gaze. Fluorescein evaluation showed central alignment with good clearance in the mid-peripheral and peripheral areas.

The patient was advised to start with no more than 6 hours of wear on this day, and to gradually increase her wear time by about 2 hours per day until reaching 12-14 hours of wear daily.

Follow-Up Care/Final Outcome

CT returned in 10 days for a follow-up visit. She reported good comfort all day long with an ability to wear the GP lenses 14 hours per day. Vision was sharp with the lenses and there was no difficulty with spectacle blur after lens removal.

Visual Acuities (with Contact Lenses):

OD: 20/20
OS: 20/20

Over-Refraction:

OD: Plano DS 20/20
OS: Plano DS 20/20

Slit Lamp Evaluation (with Contact Lenses):

Each lens positioned in a lid attached, superior central position. Movement was good in all positions of gaze. The fluorescein pattern showed central alignment and good mid-peripheral and peripheral clearance.

There was an absence of SPK. This patient continues to do well.

Discussion/Alternative Management Options

There are a number of reasons that this patient’s lenses were uncomfortable at first presentation. One was the slightly flat fitting relationship noted on fluorescein pattern evaluation. The previous practitioner had apparently fit his lenses on-K, which did not work in the long run for this patient.

Also, the lens diameter was too small, preventing any lid attachment (even with a minus carrier lenticular). Lid attachment is very important for both good long-term comfort and physiologic response. A lens that rides low tends to create problems with desiccation since the lens does not move sufficiently. It can also lead to lid awareness/irritation since the lid must travel over the lens edge with each blink, which in turn can lead to partial blinking which further dries the surface of the lens and the eye (1). A larger lens allows the upper lid to hold the lens up, which promotes better comfort and allows for a better physiologic outcome because the lens moves more freely and stays wetter.

Finally, the central lens thickness of the original lenses seemed thick. Thick lenses have a more forward center of gravity which creates more of a tendency for the lens to drop. Thinner lenses allow the center of gravity to move posteriorly, which aids centration and allows the upper lid to engage the lenticular more efficiently. Small design modifications can mean the difference between a happy patient who refers others to the practice and one who never returns and advises others to go elsewhere.

Other options for this patient were scleral GP lenses, soft toric lenses, spectacles or refractive surgery. As a chef, spectacles were not practical due to the hot, greasy working conditions in the kitchen. The patient had tried soft lenses years before and found the vision to be unacceptable, and the lenses tore frequently. Also, the care system was cumbersome and expensive. Due to this patient’s refractive error, she had been told she would not be a good candidate for various procedures, and had little interest.

If lens centration had not been achieved for patient CT, scleral GP lenses could have been considered. Scleral GP lenses tend to center well, provide the patient with GP quality vision, and sclerals might be a good option when cooking in a greasy kitchen environment.

It was common practice in the PMMA and low Dk GP era to provide the patient with a wearing time schedule. Generally, this starting with a first day wearing time of 3 to 4 hours and increased by 2 to 3 hours each following day until maximum wearing time was achieved. Many practitioners recommend longer initial and adaptation wearing times. One thought is that daily wearing time is not as important as your patient waiting for one-half to one hour in the morning before they apply their lenses to rejuvenate their corneas with oxygen prior to applying their lenses and removing the lenses one-half to one hour before bedtime.

Spectacle blur was very common in the days of PMMA and low-Dk lens wear. With today’s higher-Dk materials, oxygen deprivation spectacle blur has been minimized. However, corneal distortion and resulting spectacle blur can still be induced mechanically if the GP lens base curve does not contour the cornea and localized areas of touch occur.

At annual examinations, update your patients about new and improved technologies. For example, in this case discuss the status of hyperopic LASIK and other refractive options.

References

Bennett ES. Lens Design, Fitting, and Evaluation. In Bennett ES, Hom MM. Manual of Gas Permeable Contact Lenses, 2nd ed., Elsevier Science, St. Louis, MO, 2004, 91-113.

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