GP Lens Case Grand Rounds Troubleshooting Guide – 49

Corneal Reshaping: Robert L Davis, OD

Background

One week prior to lens dispensing, AP, a 15-year-old student, was brought into the office by her parents after reading our newsletter explaining the benefits of orthokeratology. Both parents have been wearing GP contact lenses for twenty plus years due to their advancing myopia. AP’s parents were investigating various contact lens options for their daughter with the primary goal to stabilize the advancing myopia.

AP reported distance vision becoming increasingly blurry recently with the right eye worse than the left. AP’s immediate goal was to no longer wear glasses as her primary source of vision correction. She was very active in sports and perceived glasses as troublesome because they restricted her vision and were a distraction during rigorous activities.

During the case history a discussion occurred discussing the advantages and disadvantages of GP lenses and soft lenses. AP was not taking any medications nor had any history of allergies. AP was very excited about the possibility of no longer requiring a visual correction during her waking hours. Her last eye examination was one year ago with her previous optometrist.

Test Procedures, Fitting/Refitting, Design & Ordering

Entrance visual acuity with current spectacles at distance:

OD: -2.50 DS 20/30
OS: -1.00 DS 20/30

Near visual acuity without correction:

OD: 20/20
OS: 20/20

Uncorrected visual acuity at distance:

OD: 20/200
OS: 20/80
OU: 20/80

Pupillary responses were equal, round and reactive to light and accommodation with no afferent pupillary defect. In normal room illumination, pupil size was 3.0 mm OD and OS. In dim illumination pupil size was 4.5 mm OD and OS. Versions were smooth and full OU.

Manifest refraction was as follows
:

OD: -3.00 DS 20/15
OS: -1.50 DS 20/15

Keratometry:

OD: 44.50 @ 180; 44.50 @ 090 with no distortion
OS: 44.50 @ 180; 44.50 @ 090 with no distortion

Soft monthly disposable and soft daily contact lenses were discussed as well as the costs and follow-up evaluations. AP was mildly interested in soft contact lenses to change her eye color and the parents were very interested in GP lenses because of their prior contact lens history. AP’s primary visual expectations after our discussions were to see well without wearing her spectacles or contact lenses during the day. The costs and minimum follow-up visits of one day, one week, one month, three months and six months were discussed.

AP was a good candidate for overnight orthokeratology based on her refractive error, corneal curvature, good corneal health, minimal corneal cylinder, average pupil size, and good motivation and visual expectations. She was a good candidate for orthokeratology and was scheduled for an educational program in one week for application, removal and lens hygiene.

Lens Dispensing:

AP returned to the office excited about her orthokeratology dispensing visit. Entrance visual acuity with current spectacles at distance was 20/30 OD and OS. Glasses were not ordered with her new prescription because of the changes in her refractive error that was expected to occur during the next few days. The slit lamp examination was unremarkable.

Corneal topography was performed on both eyes with the following simulated keratometry (SimK) values:

OD: 45.50 @ 180; 45.50 @ 090
OS: 45.50 @ 180; 45.50 @ 090

The following lenses were ordered from her initial eye examination determined by the corneal curvature, refractive error, corneal eccentricity and sagittal height. The reverse geometry lens design is configured to compress the central corneal surface to undo the central myopic wave power. The flat topography value OD 45.50 and OS 45.50 and the spherical component of the refraction -3.00D OD and -1.50D OS required a base curve selection of OD 8.28mm and OS 7.99mm. The base curve is fit flatter than “K” in the amount necessary to neutralize the patient’s prescription with an added 0.75 compression factor to allow for regression. As the contact lens compresses the tissue centrally the reverse curve allows the corneal tissue to reform into the space created by the contact lens/corneal sagittal height.

The reverse curve is determined by the neutralizing prescription, corneal eccentricity and corneal curvature. The flat contact lens base curve eventually will lift off the cornea requiring the reverse curve to help bring the contact lens back to the corneal surface to receive the alignment curve. The alignment curve centers the lens and prepares the cornea/contact lens relationship to position parallel onto the corneal surface. This alignment curve locks down the contact lens on to the cornea surface. The peripheral curve is designed to receive tears to float the contact lens and for tear exchange. The lens diameter is usually between 10.0mm and 11.0mm with an optical zone of approximately 6.0mm for good lens centration.

OD:

Base Curve Radius (BCR) 8.28 mm
Reverse Curve 6.61/.6 mm
Alignment Curve 7.58/1.0 mm
Peripheral Curve 11.00/.4 mm
Lens Thickness 0.19 mm
Overall diameter (OAD) 10.0 mm
Optic zone diameter (OZD) 6.0 mm
Power +0.75D
Boston XO Blue

OS:

Base Curve 7.99 mm
Reverse Curve 6.95/.6 mm
Alignment Curve 75.8/1.0 mm
Peripheral Curve 11.00/.4 mm
Lens Thickness 0.19 mm
OAD 10.0 mm
OZD 6.0 mm
Power +0.75D
Boston XO Blue

A drop of anesthetic was instilled OU. The contact lenses were applied and allowed to settle. Fluorescein was instilled to assess the lens-to-cornea fitting relationship. The lenses were well centered OU, with an adequate central zone of touch, adequate paracentral clearance, good mid-peripheral alignment, adequate peripheral edge lift and the desired bulls eye appearance. The visual acuity with contact lens wear was 20/20 OD and OS.

Patient Consultation and Education

An explanation of the expected outcome over the next few days was discussed. The first few days are difficult to accurately predict the results of the orthokeratology procedure. If an uncorrected ametropia exists after the first day there are options available to provide adequate vision. AP can wear the reverse geometry GP lens during the day or temporarily wear soft lenses until the corneal reshaping provides complete correction.The past spectacle correction will not be a viable option to provide adequate vision.

During the first year of orthokeratology, if a lens change is necessitated to achieve an optimal result an exchange (without an additional fee) is made. Lenses must be returned in order not to confuse the proper lens used for overnight wear or a charge is instituted. Application and removal instruction was given and adequately demonstrated. A sample of Alcon’s Unique pH multipurpose solution was given and proper lens care and storage were discussed. I also advised a daily drop of SupraClens to ensure adequate protein removal and Miraflow (CooperVision???) surfactant cleaner for nightly lens cleaning.

AP was instructed to wear the lenses overnight and return to the office for a morning appointment the next day. She was also educated on the use of rewetting drops. Prior to leaving the office she removed her lenses and returned home wearing her old spectacle lenses.

Follow-Up Care/Final Outcome

One Day After Lens Dispensing:

AM had removed her lenses upon waking up in the morning. She had been wearing the lenses for 8 hours. She was slightly aware of the lenses but to a lesser extent than when she applied them prior to bedtime. Her entrance visual acuity without lens wear was 20/30 OD and 20/25 -1 OS.

Corneal topography was performed resulting in the following simulated keratometry (SimK) values:

OD: 43.00 @ 180; 43.50 @ 090
OS: 43.50 @ 180; 44.00 @ 090

Fluorescein evaluation of the lenses revealed good centration, an adequate central zone of touch of about 4 mm, adequate paracentral clearance, good mid-peripheral alignment, and adequate peripheral edge lift OU.

Manifest Refraction:

OD: -0.50D 20/20
OS: -0.25D 20/20

Slit lamp examination of both eyes revealed no abnormalities including an absence of corneal and conjunctival staining. Corneal topography showed a central flattening of the cornea. The flattened treatment zone appeared to be centered over the corneal apex/pupillary zone confirming overnight lens centration. The paracentral area exhibited a sharp steepening zone flattening out to the periphery.

AP was instructed to bring her lenses in at each appointment visit in case the lenses needed to be polished or exchanged. She was advised to wear the lenses each night with morning removal and daily morning cleaning with Miraflow. She was also advised to remove and appropriately clean the lenses and apply one drop of the daily protein remover SupraClens(Alcon) to the solution in the case. The initial fit and visual acuity did not warrant any lens parameter changes so a one week follow up appointment was scheduled.

One Week After Lens Dispensing:

AP returned for an office visit no longer needing to wear any correction during her waking hours. She was wearing the lenses 8-10 hours per night and digitally cleaning them as instructed with Miraflow and soaking in Unique pH each morning with a drop of SupraClens in the case. Her vision was clear all day and was happy with the visual outcome. Lens awareness was still present but much improved. She reported no complaints with lens handling.

Her entrance visual acuity was 20/20-1 OD and 20/20-1 OS. The sphero-cylindrical over-refraction was -0.25 -0.25 X 90 OD and PL -0.25 X 180 OS with 20/20 acuity OD and OS.

Corneal topography was performed resulting in the following simulated keratometry (SimK) values:

OD: 42.50 @ 180; 43.00 @ 090
OS: 43.50 @ 180: 44.00 @ 090

Fluorescein evaluation of the lenses revealed good centration, 3.8 mm central zone of touch OD and 4 mm central zone of touch OS, slightly excessive paracentral clearance OD without air bubbles, adequate paracentral clearance OS, good mid-peripheral alignment OU, and adequate peripheral edge lift OU.

A one month appointment was scheduled. She was advised to try and not wear the lenses on Friday night and make an appointment on Saturday.

One month after lens dispensing:

AP had no complaints and had been wearing the lenses nightly with the exception of the previous night. The entrance visual acuity with no correction was 20/20 OU with a refraction of +0.25 DS OD and OS.

Slit lamp examination of both eyes revealed no abnormalities including an absence of conjunctival staining. Corneal topography revealed that the treatment zone was centered and full refractive treatment had occurred in both eyes from baseline. It was decided that AP would wear her lenses during school nights and no lens would be worn on Friday and Saturday nights. AP was happy with the outcome and advised to return in three months for a follow-up visit or immediately if she observed any injection or pain.

Three Months After Lens Dispensing:

AP had no complaints and had been wearing the lenses every night except for the weekends with good vision all day long. She noticed a mild blur in the evening on Sunday night after skipping a few days. She had worn the lenses overnight the night before the appointment for 9 hours.

Her objective and subjective results were similar to the one month visit. She was completely satisfied with her vision, comfort and her part-time nightly wear schedule. She was advised to return in 3 months for a comprehensive eye examination or sooner if she had any problems.

Discussion/Alternative Management Options

In the United States one out of four individuals are myopic. Controlling the progression of myopia during childhood potentially will reduce the risk for glaucoma, retinal detachment, vitreous detachment, and macular degeneration.

The most likely candidates for the orthokeratology program are those individuals who do not like to wear glasses or contact lenses. Patients who have allergies or environmental dry eyes make wearing contact lenses during the day problematic. Athletes and computer users experience extreme lens dryness during their activities because of lens evaporation. Firefighters and individuals working in a chemical environment or one that permits smoking have problems with their lenses because of the grit and chemical toxicities.

The pediatric population represents a large potential market because of the multiple benefits of sleeping with the lenses at night and no lens needs to be worn during the day. The controlled environment at home reduces the risk of lost or broken contact lenses. No glasses are required as a back-up correction. Devoid of the problems of environmental irritants and debris and lack of hygienic problems confronted during daily routines reduces the likely adverse reactions of acute red eye syndrome.

The initial visit will determine the candidacy and the baseline for the patient. Patients should be excluded as candidates if they exhibit inflammation or infections of the eye including active blepharitis, any disease, injury, dystrophies or abnormality that affects the cornea or surrounding tissue, any systemic disease that may affect the eye or be worsened by wearing contact lenses, allergic reactions of the eye, which may be caused or exaggerated by wearing contact lenses or use of contact lens solutions, and eyes that are red or irritated, or suffer from severe dryness.

Initial corneal topographical analysis will exclude corneal anomalies such as irregular corneal astigmatism, lenticular astigmatism greater than 0.75D, keratoconus and pellucid marginal degeneration. Individuals with limbus-to-limbus astigmatism, as determined by corneal topography will also have difficulty in achieving an expected result from orthokeratology. Patients with steeper corneal curvatures and higher eccentricities tend to have a better likelihood of success. Patients with large pupils will likely suffer from halos and glare. The most important function of baseline corneal topography is to provide an initial corneal shape from which to compare subsequent topographical changes. Follow-up topography will show the present cornea shape and direct you to the modifications that need to be made to arrive at an optimal result.

The optimal characteristic bull’s eye pattern unique to orthokeratology exhibits an approximate 4mm area of central touch with 1mm of clearance over the alignment curve. Corneal staining is a sign of either mechanical irritation or physiological problems requiring immediate remediation. Debris on the inner surface of the lens is the simplest staining problem to resolve. A tight lens will trap material underneath the lens with no tear exchange. Increase fluid exchange by loosening the peripheral curve and/or the alignment curve will remediate the tight lens syndrome. Air bubbles will cause dimple veiling created by vaulting over the central cornea or the reverse zone. A base curve that is too flat increases the mechanical pressure onto the cornea creating a rubbing action on the corneal apex possibly resulting in a corneal abrasion. Individuals taking medications that impact tear volume can also create a tear insufficiency problem. Punctal occlusion has resolved many problems related to poor tear volume. Mid-peripheral arcuate staining refers to a tight peripheral curve design. The peripheral curve can be loosened (flattened) or an aspheric peripheral zone system can be designed to alleviate this problem.

When lens pressure is applied onto the cornea an indentation or distortion will show up as a lens imprint. This unwanted result is caused by a reverse curve that is too tight or a decentered lens creating an undesired contact lens-cornea relationship. Some corneas have less rigidity and a lens imprint is normal. The alignment curve and/or reverse curve can be loosened/flattened by .15mm or 0.50D to reduce the problem.

Under responders and over responders are patients who react in an unpredictable manner. These are the only scenarios that a base curve change is warranted. The base curve radius can be flattened or steepened by 0.50D increments to arrive at the appropriate prescription providing that the fluorescein pattern is normal. If the uncorrected visual acuity does not hold for an acceptable amount of time the appropriate bearing pressure is not being applied centrally. The usual cause is a slightly decentered lens position. The sagittal height of the reverse curve is often too low, resulting in no space for the central tissue to be displaced. Increasing the sagittal height or steepening the reverse curve allows more space for the central tissue to relocate. The fluorescein pattern will exhibit a wider alignment zone. Some patients’ corneas are rigid and will not be affected in a predictable behavior. Ghosting at night usually occurs when the pupil dilates at night and the treatment zone is smaller than the papillary size. Increasing the treatment zone to 6.2 mm usually will solve this problem. Patients with uncorrected astigmatism will also complain of ghosting. Increasing the central bearing by reducing the sagittal height through the reverse curve and alignment curve usually will improve this distortion.

In the morning lenses sometimes get stuck centrally on the cornea with no lens movement resulting in central staining and lens imprint. This will result in an inadequate tear flow under the contact lens. Lubrication drops or punctual occlusion will prime the lens, improving the lens to float on the cornea maintaining an ample tear exchange. Loosening the reverse curve will also cause better tear movement so the lens does not get locked down onto the cornea. At times a change in one parameter will cause a change in the corneal/lens relationship. Flattening the reverse curve might mandate a change in the alignment curve to maintain lens centration.

Post-fitting corneal topography provides a visual analysis of the corneal shape changes that have occurred during overnight lens wear. The position of the contact lens in the open-eye environment is not necessarily representative of where the lens positions in the closed eye. Sometimes the corneal curvature changes that have occurred overnight are not consistent with the predicted values. It is important to not overlook the possibility that the lens has been displaced from an induced pressure by inadvertent movements during sleeping or pressure due to the position of the face on the pillow. Therefore, corneal mapping provides the only reliable means of knowing precisely where the lens positioned during sleep. This information helps in determining the appropriate lens modifications necessary to achieve the desired outcome.

Summary/Alternative Management Plans

The objective of orthokeratology is to provide safe, overnight contact lens wear that creates a predicted refractive change and provides clear vision throughout the day without lens correction. Overnight lens wear provides a convenient method of corneal changes, improved lens tolerance without lid interaction and reduces symptoms of daytime dryness. The benefits for sports and other recreational activities without wearing a contact lens dramatically change the way GP lenses are perceived without the fear of grit getting under the contact lens, lens displacement or the drying effects of wind. Moderately nearsighted patients can now learn to swim without the panic of poor unaided visual acuity or the risk of corneal insult or lost lenses resulting from daily wear of contact lenses. Recent advances in GP lens polymers allows initial all night lens wear without the necessity of adapting to lens wear.

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