Refine Vision with Soft Toric Lenses
By Keith Ames, OD
Quickly and easily solve vague visual complaints of astigmatic patients with three tests to assess visual performance.
Soft toric contact lens wearers often present for a routine examination with vague visual complaints. For these patients, it is important to assess their current lens wear objectively. If test results demonstrate a visual deficit, a trial refitting can be easily accomplished and will frequently result in subjective improvement.
When assessing soft toric visual performance, I perform three tests: visual acuity (binocularly then monocularly), retinoscopy over-refraction in free space and biomicroscopic assessment of lens rotation. If these three tests suggest a performance problem, I am reasonably assured that a trial refitting is justified both in terms of patient time and expense.
Visual acuity is the single most important test we perform daily. The nuances of the patient's response are often as important as the response itself. That is why I don't delegate this test to technicians. I test visual acuity binocularly first. This gives a better indication of how the patient is functioning in the "real" world. Then I cover each eye and ask if one eye sees better than the other. If the patient notes a difference, I determine the acuity of the poorer eye.
This procedure gives me the opportunity to educate the patient and control expectations. If the acuity difference is minor and not related to any objective fitting deficit that can be corrected, I reassure the patient that exactly equal acuity is not expected. If the acuity difference is significant, I try to correlate it with over-retinoscopy and lens rotation.
Over-retinoscopy in free space is a quick, objective way to assess the quality of the optical system. I use lens flippers in 0.50D increments and assess the direction and crispness of the reflex. Scoping cylinder oblique to the contact lens cylinder axis suggests rotational forces are creating cross-cylinder effects. Variable or distorted reflexes could indicate irregular lens flexure or poor rotational stability.
Any of these findings in an eye with poorer than expected acuity is a strong clinical correlation and indicates a fitting problem. A word of caution: when performing retinoscopy in free space, expect slightly (0.25D to 0.50D) more plus/less minus than seen behind a phoropter due to the absence of instrument accommodation.
I observe lens rotation with the biomicroscope. Keep illumination to a minimum, align the light source and objectives straight ahead and make sure the patient's head is positioned with no turn or tilt. I also evaluate the stability of lens rotation after the patient sits back and looks around the room for a few seconds. Be careful not to underestimate rotation. A clock hour of rotation represents 30 degrees, an amount which could seriously impact vision even with low cylinder corrections.
Using Test Results
Let's look at specific patient examples and see how the correlation of these three tests can guide you to a successful refitting.
Low Cylinder Refit. A 39-year-old patient reports a longstanding history of GPC with previous RGP and soft toric corrections. He was refit from RGPs approximately six months ago into his current soft toric correction:
OD: 3.501.00 x170
OS: 3.501.00 x20
CIBA Vision Focus Torics, 8.9mm base curve
He reported poor acuity, poor comfort and excessive lens spoilage requiring frequent (one to two week) lens replacements.
A refraction showed a significant change relative to his current contact lens Rx most likely attributable to refractive changes secondary to the cessation of RGP wear. The current refraction was:
OD: 4.251.25 x180
OS: 4.001.25 x005
A trial refitting was suggested in a material which, in my experience, performs very acceptably in monthly replacement:
CooperVision Frequency 55 Torics, 8.7mm base curve
Results at dispensing and three weeks:
Visual Acuity: OD: 20/20
Over-Retinoscopy: OD: Plano OS: +0.500.50 x180
Rotation: OD: 0 OS: 10 Temporal
The patient was very happy with vision and comfort overall, and the lenses were maintaining clean surfaces after three weeks of wear. Final lenses were ordered with an axis change OS to 180 to compensate for the slight rotation observed.
High Cylinder Refit. A 32-year-old patient was seen for the first time in our clinic wearing custom toric soft contact lenses for a significant astigmatic correction. His current contact lens parameters were unknown. His refraction was:
OD: +5.506.00 x08 20/60 (amblyopia)
OS: +4.255.50 x166 20/25
Although I generally prefer fitting toric RGP lenses for this type of refractive error, the patient was highly motivated to remain in soft toric lenses so the following lenses were ordered:
OD: +5.506.00 x 08 (x 11)*
OS: +4.255.50 x166 8.9/15.0 (5.00 x166)
CooperVision Hydrasoft Torics, tolerances accepted
After approximately two weeks of wear, the patient reported blurred vision OD. Testing revealed:
Visual acuity Over-retinoscopy Rotation
20/100 Pl1.50 x170 5 Nasal
20/25 Plano 0
Interestingly, the tolerance lens received for OD was in a direction which exacerbated the poor vision due to rotation. VA, over-retinoscopy and rotation all consistently indicated an axis change was required. A new lens was ordered for OD:
+5.50-6.00 x05, tolerance (+5.00-6.00 x 05) accepted.
Visual acuity Over-retinoscopy Rotation
20/60- +0.500.50 x170 <5 Nasal
These examples illustrate several important points when contemplating axis changes to troubleshoot VA with soft torics. In the first case, I will order slight axis changes even if acuity is only slightly affected when over-retinoscopy and rotation correlate with the acuity reduction.
In the second case, even slight rotation will seriously impact vision with high cylinder corrections. Be careful not to accept large deviations in axis with tolerance lenses. On the other hand, the predictability of these results clearly shows the quality and accuracy of soft toric manufacturing today.
Objectively evaluating lens performance improves practice efficiency by reducing chairtime without sacrificing patient outcomes. In fact, my experience shows improved outcomes when testing time and reliance on subjective (variable) test results is reduced.
Soft vs. RGP
Type of astigmatism helps me decide between RGPs and soft torics. With-the-rule astigmatic patients are generally best fit with RGPs. WTR eyes usually have minimal residual astigmatism, and the mechanics of lens movement on the eye are favorable for a successful RGP fit. If the eye has less than 3.00D of corneal toricity, I will consider a spherical design, although eyes with 2.25D to 2.75D of toricity often benefit from toric designs. Eyes with 3.00D or more of toricity almost always benefit from torics. Against-the-rule astigmatic eyes usually exhibit significant residual astigmatism and will do best with soft torics. ATR eyes with minimal residual astigmatism can be fit with either lens type and can do well with RGPs, especially if lid configuration allows for larger diameter lid-attached fitting to improve lens stability.
I still find soft toric fitting trial and error. I do not choose lens designs based on parameters such as thickness profiles and ballasting as much as consistent quality, convenient packaging, pricing and company support in trial lens and exchange policies. I satisfy almost all of my patients' needs using two or three companies' products. It does the patient little good to fit a "perfect" custom soft toric lens if the patient stops wearing the lens because he can't afford to replace it often enough to prevent spoilage problems. I fit lenses that are affordable enough to replace at least monthly whenever possible. My clinical experience shows this is almost always feasible.
The best approach in discussing these options with the patient is to not discuss them. I make my recommendations based on objective findings and clearly and unequivocally recommend to the patient the lens modality I think is best for him. It is clear to the patient that I am advising the lens choice that will provide the best vision and eye health at the lowest possible cost. Most patients want and accept this approach. If a patient objects to my recommendation, I will then discuss the options and be sure that the patient understands the choice he is making.
*Note: Tolerances accepted are in parentheses ( ).
Dr. Ames is in private practice in Chilicothe, Ohio, and a technical and marketing consultant to the contact lens industry.