Application of scleral lenses in the normal eye with limbus-to-limbus astigmatism

by Thomas P. Arnold, O.D.
Today’s Vision Sugar Land, P.A.

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Abstract

Purpose: To describe a clinical case where a patient was successfully transitioned from a custom soft toric lens to a scleral lens for improved vision
and comfort.

Methods: A comprehensive ophthalmic examination that included topography, trial lens evaluation and ocular computerized tomography for the initial lens selection. Lenses were adjusted as needed to achieve a desirable fit.

Results: After assessing the limitations and poor performance of custom soft toric lenses in the high astigmat with limbus-to-limbus astigmatism, a young, healthy patient was successfully refit with the Zenlens from Alden Optical.

Conclusions: Scleral lenses are an acceptable alternative to custom soft toric lenses in cases where the high degree and topography of corneal astigmatism interferes with a comfortable fit.

Keywords

Limbus-to-limbus astigmatism
Custom soft toric contact lenses
Scleral contact lens
Zenlens
Prolate cornea
Zeiss Cirrus OCT
Horizontal visible iris diameter (HVID)

Introduction

A seventeen year-old Asian female (MZ- DOB 09/30/1997) presented in our office for a comprehensive eye examination and contact lens evaluation on April 2, 2015. MZ had previously worn soft contact lenses but was not happy with them and did not bring them to the initial examination. She desired to resume contact lens wear if clear, comfortable vision could be achieved. In answer to the history form question “Concerns about your vision”, MZ wrote,
“It keeps worsening.”

Case Report

MZ’s medical history was unremarkable.  She had no known allergies and was not taking any medications.  She reported that her grandmother had cataracts and diabetes.  Her mother had hypertension.  Otherwise, the family history was negative for any eye diseases.   Her main hobbies were reading and working on the computer (3+ hours/day).

Current eyeglass correction –
OD -0.50 – 3.00 X 007    BVA 20/30
OS -1.25 – 3.00 X 178       BVA 20/30

Examination:

Uncorrected VA – OD 20/200
                                  OS 20/200

Autorefraction – Zeiss iProfiler:

                        OD -0.75 – 3.50 X 001
                        OS -1.25 – 3.75 X 001

Keratometry – Zeiss iProfiler:    

                        OD 40.50@178/44.00@088
                        OS 40.25@001/43.50@091

Manifest refraction:

                        OD -1.00 – 3.50 X 002    BVA 20/25
                        OS -1.50 – 3.75 X 002     BVA 20/25

Intraocular pressure – iCare tonometer:

                        OD 20 mm Hg
                        OS 20 mm Hg

Slit-lamp examination – Topcon SL-5E

                        Corneas clear OU
                        Anterior chamber – deep and clear OU
                        Lens / media – clear OU

Fundus examination:

                        OD C/D 0.2/0.2; macula; periphery – normal
                        OS C/D 0.2/0.2; macula; periphery – normal

Topography – Medmont E300 (attached)

                        OD 41.22@017/44.66@107 – DK 3.44 D
                        OS 40.54@004/43.85@094 –  DK 3.31 D

Initial lenses ordered:

                        OD ProClearToricXR 8.8/14.4/ -1.00 – 3.25 X 180
                        OS ProClearToric XR 8.8/14.4/ -1.50 – 3.75 X 180

Follow- up (05/30/2015):

BVA (soft torics): OD 20/40; OS 20/30

MZ reported that the ProClear XR lenses were no better than her previous lenses. Wearing time was minimal as she only wore them when “necessary.” She complained of fluctuating vision especially after the blink. In our clinical opinion, the limbus-to-limbus extension of the corneal astigmatism led to an unstable and less than desirable fit. Various contact lens options were discussed and the patient was open to trying an RGP miniscleral design. 

As her corneas exhibited a normal, prolate shape of with-the-rule astigmatism, the initial trial scleral lenses were of that design.

Trial lenses:
#1 OD Zenlens 4.200 sag/ 16.0 OAD/ Prolate / -2.00 D
OS Onefit 2.0 8.20 BC/ 14.9 OAD/ Prolate/  -0.50 D

Slit-lamp examination of these lenses revealed two important findings:
1.) OAD was too small in both the lenses.
2.) More vault was needed

MZ’s horizontal visible iris diameter (HVID) was approximately 13.0 mm in both eyes. It was immediately apparent that a much larger lens would be needed to adequately vault the cornea.

These are the instructions on initial lens selection from the Zenlens Brochure Fitting Guide:

Lens Design Selection

Select lens diameter based on corneal diameter measurement or estimation:   

• For smaller corneas (11.7 mm or smaller), the 16.0 mm design is recommended
• For larger corneas (11.8 mm or larger), the 17.0 mm design is recommended

Select the lens design based on the corneal shape or indication:

• Choose the prolate design for keratoconus or normal corneas with ocular surface disease

Initial Diagnostic Lens Selection – Prolate Design

• For normal corneas or mild keratoconus, choose the 4500 (16.0mm)
  or 4900 (17.0 mm) SAG

Based upon these guidelines, the following lenses were inserted:

#2 OD Zenlens 7.9 BC /4.900 sag/ 17.0 OAD / Prolate / -2.00   over-refraction  -7.25 sphere 
VA 20/30

OS Zenlens 7.9 BC/4.900 sag/ 17.0 OAD / Prolate / -2.00*  over-refraction  -3.00 sphere 
VA 20/30

(*Note: we have two fitting sets of both Zenlens and Onefit 2.0)

Slit-lamp examination:

            OD excessive clearance
            OS more clearance than required – not as great as the right eye.

OCT – central vault:

            OD – 552 microns
            OS – 279 microns

Centration, limbal clearance, edge landing were all very good.  MZ reported good comfort and crisp vision. She noticed the stability of the visual image.

Plan was to order the above lenses with the request to reduce the central clearance approximately 150 microns in both eyes.

Final lens parameters ordered from Alden Optical were:

            OD Zenlens 7.8 BC/ 4.620 sag/ 17.0 OAD / Prolate/ -8.62

            OS Zenlens 7.8 BC/ 4.900 sag/ 17.0 OAD/ Prolate /  -5.00

1^stDispense visit (06/15/2015)

Lenses above were dispensed.

BVA (new lenses):

            OD count fingers
            OS 20/25 –

Over-refraction:

            OD  +3.50  sphere   VA 20/25
            OS   -0.50 sphere    VA 20/25

OCT- central vault:

            OD 350 microns
            OS 270 microns

Slit-lamp exam:

            OD – noticeable edge lift. Patient is aware of lens
            OS – acceptable landing. Patient is comfortable

Plan:    

1. Reorder OD lens only. Goal is to reduce vault my 80 microns (approximately); order 1 steep APS (scleral landing zone)
2. New Zenlens – 7.8 BC/ 4.540 sag/ 17.0 OAD/ Prolate/ -5.12 sphere/ 1 steep APS

2^ndDispense visit (06/24/2015)

OD lens with parameters listed above was dispensed in office.  Vision was very poor and lens exhibited a very large edge lift. Sterile saline could not be retained within the lens bowl but leaked out immediately.  The patient reported that it was very uncomfortable. It was determined that the lens was defective and was therefore not dispensed to the patient.

A new trial lens was placed on the right eye.  The trial lens had the following parameters:

OD Zenlens 7.8 BC/ 4.900 sag/ 17.0 OAD/ -2.00 Prolate / over-refraction -2.75 sphere
VA 20/20

OCT – central vault (trial lens)
            250 microns

Plan:

1. Re-order new OD Zenlens. Increase sag value by 50 microns to allow for settling
2. Return defective lens.

3^rd Dispense visit (07/06/2015)

OD Zenlens (new)      7.8 BC/ 4.95 sag/ 17.0 / Prolate / -4.75 sphere
OS Zenlens (current) 7.8BC/ 4.90 sag/ 17.0/ Prolate/ -5.00 sphere

BVA:

            OD 20/30  over-refraction – Plano
            OS 20/30   over-refraction – Plano

Slit-lamp exam:

            OD – moderate lens inferior decentration. Minor edge lift at 3-9 o’clock
            OS – good PLTL alignment. Landing was smooth and even 360 degrees

Plan:

1. Released patient with lenses above
2. Dispensed proper cleaning and care regimen
3. Return to clinic in 3-4 weeks

Progress visit (08/11/2015)

Wearing time today – 4 hours; Average wearing time – 10+ hours
Chief complaint – lenses fog occasionally.  Not a major issue
Solutions: Optimum RGP Daily Cleaner; UniquePh (disinfecting);
OD Zenlens    7.8 BC/ 4.95 sag/ 17.0 / Prolate / -4.75 sphere
OS Zenlens    7.8 BC/ 4.90 sag/ 17.0 / Prolate/  -5.00 sphere

BVA:

            OD 20/25-2   over-refraction  +0.50 sphere   20/25
            OS 20/30   over-refraction  – 0.25  sphere   20/25

Slit-lamp exam:

            OU – good centration; adequate limbal clearance; no conjunctival blanching or prolapse

OCT:

            OD – 193 microns central vault after 4 hours wear

Plan:

1. Add ProGent(Menicon) cleaner to regimen. Use every 2 to 4weeks, as needed
2. Use Oasis Plus artificial tears – 2 to 3 drops in lens bowl before topping up with Addipaks inhalation saline. Observe if comfort is increased and fogging issues decrease
3. Return for visit in 2 to 3weeks

Progress visit (09/29/2015)

Wearing time today – 10 hours; Average wearing time – 10-14 hours
Chief complaint – none.  Lovedthe lenses. Wearing time has increased with addition of Oasis Plus artificial tears. No redness or spectacle blur upon removal 

Solutions: Optimum RGP Daily Cleaner; UniquePh (disinfecting); ProGent Cleaner

OD Zenlens    7.8 BC/ 4.95 sag/ 17.0 / Prolate / -4.75 sphere
OS Zenlens    7.8 BC/ 4.90 sag/ 17.0 / Prolate/  -5.00 sphere

BVA:

            OD 20/25-2   over-refraction  +0.50 – 0.75 x 028    20/20-2
            OS 20/30 -2     over-refraction  – 0.75 -0.50 x 170   20/25

Slit-lamp exam:

OU – good centration and central clearance.  No conjunctival impingement or vascular engorgement despite long wearing time

Plan:

1. Monitor visual acuity in left lens. No patient complaints about vision at this visit
2. Return for visit in 2 to 3 months or sooner if vision concerns develop

Discussion:

Two issues made this a challenging, yet rewarding, fit:

First, she had a fairly large cornea as evidenced by the horizontal visible iris diameter (HVID) of approximately 13 millimeters despite her small body frame. This required a moderate sized lens (17.0 mm OAD) rather than the more common sizes used in our clinic (14.6- 15.6 on average). MZ had to learn to handle this larger lens.

Second, the fact that the astigmatism was not confined to the central cornea but extended to the limbus, particularly in the right eye, made the landing and edge profile all the more critical. This may have contributed to the larger number of lenses used in the right eye to achieve a desirable fit.

One must be mindful when fitting a spherical lens on a toric cornea that lens flexure may affect visual acuity. It is probable that this contributed to the sphero-cylindrical over-refraction in the left eye as the last progress visit.  Since the patient was not complaining, this was noted but no lens changes were made at that visit.   We were aware of this issue and will continue to monitor in the future.

Conclusion:

This young female with moderate limbus-to-limbus astigmatism was refit from a custom soft toric lens into a spherical scleral lens with good results.  A longer and more comfortable wearing time was achieved with the Zenlens.

References:

Zenlens Brochure and Fitting Guide.pdf (www.aldenoptical.com/products/soft-specialty/zenlens)

Contact Lens Spectrum, Volume 30, Number 2, February 2015, pages 22-27. Specialty Lens Designs for “Normal” Eyes. Davis, Robert, OD, FAAO; Eiden, S. Barry, OD, FAAO

Contact Lens Spectrum, Volume 30, Number 5, May 2015, page 48. Adjusting Sagittal Depth When Fitting Scleral Lenses. DeNaeyer, Gregory W., OD, FAAO

Advanced Ocular Care, January/February 2015, pages 56-57. The Art of Contact Lens Fitting.

Olafsson, Harald E., OD, FAAO

Review of Cornea and Contact Lenses, September 2015, pages 22-25. Options Abound:

 A 2015 Report on Custom Contact Lenses.  Bennett, Edward S., OD

Review of Cornea and Contact Lenses, September 2015, pages 26-31. Critical Measurements to Improve Scleral Lens Fitting. Jedlicka, Jason, OD.

Review of Optometry, Volume 152, No. 8, August 15, 2015, pages 50-56. Real-World Factors That Affect Contact Lens Success. O’Dell, Leslie, OD

Optometry and Vision Science, Volume 91, Number 12, December 2014. pages 1462-1466.

A Comparison of the Short-Term Settling of Three Scleral Lens Designs. Kaufman, M.J.; Gilmartin, C.A.; Bennett, E.S., Bassi, C.J.