GP Lens Case Grand Rounds Troubleshooting Guide – 50

Low Myopia (≤ 1.50D): Gary Osias, OD

Background

JF was a long term daily soft contact lens wearer who, for many years, was successfully wearing soft monthly replacement contact lenses. Upon learning of the existence of corneal reshaping GP lenses, JF wanted to try this new option thinking that they would be better for his lifestyle as a rapid transit operator and fisherman. Also influencing JF’s decision was the development of inferior limbal neovascularization from low grade corneal hypoxia associated with many years of soft lens wear.

Test Procedures, Fitting/Refitting, Design & Ordering

Visual Acuities (Unaided):

OD: 20/70-
OS: 20/200

Manifest Refraction:

OD: -1.00 DS 20/15-
OS: -1.62 DS 20/15

Keratometry/Corneal Topography:

OD: 44.12 @ 168/44.62 @ 078
OS: 44.50 @ 180/44.62 @ 90

The pupil diameter in room/dim illumination was 5/6mm; the horizontal visible iris diameter was 12.1mm; the vertical palpebral aperture size was 10mm and moderate lid tension OU.

Diagnostic lenses: Paragon CRT

OD: Base Curve Radius (BCR): 7.90mm
Return Zone Depth .525
Landing Zone Angle 33˚

OS: Base Curve Radius (BCR): 8.00mm
Return Zone Depth .525
Landing Zone Angle 34˚

Spherical Over-Refraction:

OD: plano 20/20
OS: plano 20/20

Slit Lamp Examination:

OU: Both vertical and lateral centration were good with a bulls-eye fluorescein pattern (central bearing, intermediate pooling, intermediate/peripheral bearing and peripheral edge lift).

Lenses Dispensed: the aforementioned lenses were dispensed to this patient.

Patient Education and Consultation

JF was instructed on proper lens handling and care. The lenses were to be inserted before bed and worn a minimum of six hours the first night with a follow-up visit scheduled for early the next morning with the lenses still on. Rewetting drops were to be instilled upon awakening in the morning.

JF understood that vision the first day with the lenses removed would be markedly improved, perhaps even 20/20; however, whatever the improved vision started out to be, it would likely diminish towards evening.

Follow-Up Care/Final Outcome

The next morning, after the first night of wear, JF reported good vision with the contact lenses on and reasonable comfort. Wearing time at the time of the visit was 9 hours total of which 8 were sleeping hours.

Visual Acuities (with contact lenses on):

OD: 20/20 Spherical Over-refraction: Plano 20/15
OS: 20/20 Spherical Over-refraction: Plano 20/20

Visual Acuities (without Contact Lenses):

OD: 20/20 Spherical Over-refraction: -0.25DS 20/15
OD: 20/25 Spherical Over-refraction: -0.25DS 20/20

Slit Lamp Examination:

OU: Fluorescein pattern as above with good centration and movement.
No corneal staining was evident after lens removal.

JF was instructed to continue with night-time wear and return for follow-up care in one week.

After one week of wear JF reported improved vision which lasted all day, good comfort, and consistent vision. The perception of haloes around lights at night was slightly greater than with his previous soft contacts.

Visual Acuities (without contact lenses):

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

Spherical Over Refraction:

OD: Plano
OS: Plano

Slit Lamp Examination:

An absence of corneal staining existed OU.

JF was instructed to continue with night-time wear and return for one final follow-up visit in three weeks.

After one month of wear, JF reported good vision which lasted all day and even the following day if one night of wear was omitted. Night-time haloes around lights had greatly diminished. JF was quite pleased with his vision.

Visual Acuities (without Contact Lenses):

OD: 20/15
OD: 20/15-

Spherical Over-Refraction:

OD: Plano
OS: Plano

Slit Lamp Examination:

OU: No corneal staining

Keratometry/Corneal Topography:

OD: 43.87 @ 180; 44.00 @ 090
OS: 43.87 @ 180; 43.87 @ 090

Discussion/Alternative Management Options

As with all treatment therapies, candidate selection is of vital importance. The usual refractive data criteria were all met for JF: low myopia, little/no astigmatism, nearly spherical corneas, average size pupils, etc. Physiological considerations also were favorable: adequate tear layer and good anterior segment health except for the corneal neovascularization secondary to soft lens wear. (The neovascularization turned into ghost vessels by JF’s six month office visit.) Psychologically, JF was ready for a change into something new and corneal reshaping appealed to JF’s desire to be lens-free during the day without having to resort to surgery.

Initial lens selection was “strictly by the book.” Using the Initial Lens Selection Guide provided by the manufacturer, lenses were selected for JF and due to their excellent performance became the final outcome lenses of choice. My experience fitting these lenses has shown a high correlation between the Initial Lens Guide and the final outcome lenses for low myopic patients. This correlation is not quite as high for moderate/moderate-high myopic patients, especially if astigmatism is involved. If the initial lenses are not exactly correct, they only need minor adjusting of one/or rarely both of the two primary fitting criteria, the return zone depth or the landing zone angle.

It is recommended to provide the patient with an idea of what visual acuity to anticipate after the first night of corneal reshaping and approximately how long it will take to achieve final outcome visual acuities. My experience with low myopic patients has shown that most patients achieve 20/20 visual for, at minimum, a few hours after just one night of lens wear. Typically, I will set their expectation level to “close” to 20/20 so that if, in fact, we do achieve 20/20 expectations have been exceeded and patients are overjoyed. It is also typical for low myopic patients with proper fitting lenses to have unaided 20/20 or better visual acuity lasting the entire day and evening after only 3 or 4 nights of lens wear. If one week has transpired and good results have not been achieved with a low myope, lens design changes are indicated.

Many variables exist which, to a greater or lesser degree, can affect the outcome with corneal reshaping contact lenses. Tear layer issues, regular and irregular astigmatism, ocular allergy, pupil diameter, and lid tension are just a few. Corneal thickness and resiliency may also play a role. However, whatever the variables may be, their impact on success seems to be lesser for patients with low myopia when compared to patients with higher myopia. Treating the low myope, therefore, is probably easier to do and a good place to start if you are contemplating adding corneal reshaping to your contact lens practice.

Resources

  1. Corneal Refractive Therapy Training Manual and Dispensing Guide
  2. Paragon Vision Sciences

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