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Grand Rounds :
How to help a patient who sees too well: a case of refractive adaptation.
Subjective
JM is a Caucasian female of 56 years old, referred by her ophthalmologist to be fitted in contact
lenses. She is working as a manager in a college sport center and has a limited autonomy
because of her visual condition. Her visual needs are mainly at computer distance but she has
to rely also on some good vision at distance. She is not driving but would want to do so, if her
vision can be improved.
Referral letter from this doctor indicates that she is known as a keratoconus patient who
underwent full thickness corneal grafts OU (not specified when). She presents with an unstable
corneal condition with ectasia at the junction of the graft OD. Pachymetry reveals thicker
corneas compared with normal: 575 um OD and 716 um OS. The doctor wants the patient to be
fitted in contact lenses to improve her visual condition.
Objective
Entering visual acuity were 20/100 OD and 20/200 OS with her actual glasses. Her refraction
gives OD -12.00 -10.00 x 80 20/50 (PH 20/40) and OS -10.25 -4.50 x 150 20/60 (PH 20/50).
Topographic maps reveal an oblate corneal surface with high level of astigmatism OU. SimK
values are 47.3 x 58.4@74 OD and 46.3 x 53.6 @50 OS. Orbscan posterior float indicates corneal
ectasia OD , which is not present on OS. However, astigmatism pattern on the left eye shows
high irregularity.
Ocular health exam under dilatation is within normal limits.
Assessment
Post-op corneal ectasia OD ; oblate corneal post-graft pattern OU, irregular astigmatism OS.
Plan
The first trial of contact lenses was made with large diameter scleral lenses, with a reverse
geometry profile. It was not successful because of the presence of the corneal ectasia OD.
Regular scleral lenses allowed to vault the cornea with more efficacy but the central clearance
was too high and the fit was not considered acceptable.
We then opted for a piggy back system with the use of custom silicone hydrogel lens (Blanchard
Lab, Exception, BC 8.3/ Diam 14.8 / +1.00Pwr) – other silicone hydrogel lenses fitting not welll
on such corneas (fluting). A rigid contact lens was used on top of these soft lenses. Dyna
Intralimbal Z cone series lenses are used with the following final parameters : BC 6.3 Diam 8.8 pc
steep 2 -13.50 OD BC 6.50 diam 8.8 pc steep 1 -18.00 OS, made in Boston XO2. At the delivery
visual acuity was 20/30 OD and 20/25 OS. RGP lenses were slightly positioned inferiorly but the
overall fit was found acceptable. Education was provided on insertion, removal and care of the
lenses.
On the follow-up, patient reported discomfort and a frequent loss of the right lens upon blinking
or when adopting lateral gaze. She did not wear lenses that much because of these annoyances.
It was then decided to refit the patient with a mini-scleral lens while keeping the piggy back in
place to alleviate any touch on the ecstatic part. After several trials, One Fit –keratoconus
profile- contact lens was provided (OD BC 6.3 Pwr -14.00D Diam 13.8; OS BC 6.4 -18.75 Diam
13.8, in Boston XO2) which lead to an improved acuity of 20/25 OD and 20/20 OS. Patient was
very thrilled with this level of visual acuity and she reported that she did not see that well since
many years. Education on handling of sclera lenses was provided.
A month later, patient was seen back and reported a failure again to wear her lenses. This time
she reported very good comfort with the lenses on, they were very stable and she did not
experience any lens loss during the last weeks. However, she reported dizziness and headaches
after 45 to 60 minutes of wear. She was not able to look around except in primary gaze without
suffering from nausea and malaise. She just told: “ I am seeing too much. It makes me sick!”
We decided to alter the power of the lenses to help her to get use to her new vision. Our goal
was to give her the legal visual acuity to drive a car (20/40 monocularly) and to complete the
correction in glasses, with power for distance and near.
New lenses were ordered with OD -10.00 (instead of -14.00D) and OS -14.00 (vs -18.75D). At the
delivery, we tried with trial frame several combinations of lenses over the contact lenses. The
patient felt well with -3.25 OD and -3.00 -1.00 x 180 OS for visual acuity of 20/25 OD and 20/30
at distance. At near, a power of +2.75 D provided 0.5 M visual acuity. Straight line bifocal lenses
were recommended to ease the patient’s adaptation (vs progressive lenses).
Patient was seen 6 weeks later and felt very happy with her vision. She got used to her lenses
without any problem. Most of the time she relies on her contact lenses only and uses her glasses
to drive or when it is necessary to see better at distance during her work. She can do most of
her day-to-day activities with her contact lenses only.
In the future, we could plan to modify the contact lens power in order to reach the full visual
correction with this modality, keeping reading glasses only. However, the patient feels that she
is fully functional and gained a lot of autonomy with her actual visual equipments. She is not
ready to make any change for the moment.
Many elements can explain the outcome from the first fit: refractive adaptation, changes in the
size of perceived images, magnification from the use of contact lenses vs glasses (considering
high myopic powers) and the presence of lenses on the eye. Each of these elements will be
discussed.
CONCLUSION
This case is unique in the way that we had to deal with a patient who, after many years of
altered visual acuity, regained almost normal vision. “Too much info” for the brain can be
disturbing and refractive adaptation has to occur. Sometimes, this new environment is
challenging to the point that the prescription has to be modified to ease the patient adaptation.
Looking at her visual demand, and respecting her capacity to adapt it was possible to find a
combination of lenses (piggy back system), to be used in conjunction with glasses, who provided
the optimal visual outcome. This case asked us to think out of the box and to perform “creative
optometry”.