One of the great joys of contact lens care is in the many ways that practitioners can serve to improve their patients’ quality of life. This certainly holds true for our more senior members of society: those who have presbyopia. Some cases are straightforward; others are more complex and sometimes downright surprising. This article will present a series of both types of cases from clinical practice.
THE STARGAZING PROFESSOR
A 72-year-old retired college professor presented with a very specific request. In his retirement, he had taken up stargazing. “I want to be able to clearly view the sky through my binoculars, then consult my celestial map,” which he had in hand. “My glasses get in the way of the binoculars.”
His spectacle prescription was as follows:
OD –1.75 –0.75 x 175, +2.50D add, 20/20
OS –1.25 –1.50 x 005, +2.50D add, 20/20
His keratometry readings were as follows:
OD 43.50/44.25 @ 089
OS 43.00/44.50 @ 095
Factoring in the Astigmatism When corneal and spectacle astigmatism match, as they do in this case, we can consider a host of contact lens options. Single-vision contact lenses would solve the problem of viewing through the binoculars, but they would not allow for near viewing of the celestial map. Reading glasses would need to be slipped on, which would not offer the convenience requested by this patient. The most convenient option was a multifocal contact lens.
Simultaneous Versus Translating Many multifocal lenses are designed to have both distance and near vision enter the pupil at the same time (simultaneous vision optics). This patient’s need to view the night sky precluded the practical use of these designs. I therefore recommended that we pursue a translating corneal GP design. With these designs, patients view through the upper portion of the contact lens, which provides solely distance correction, in straight-ahead gaze; when patients shift their gaze downward, the lens translates up so that the line of sight views through only the reading correction.
Segment Height Placement If a patient’s lower lid is tangent to the lower limbus (Figure 1), a good starting point for segment (seg) height placement is 1mm below the geometrical center of the lens. For example, the geometrical center of a 10.0mm diameter lens is 5mm, so place the seg 1mm below this, or at 4mm. If the lower lid is slightly above the lower limbus, the lid will hold the seg higher, so lower its placement accordingly. If the lower lid is below the lower limbus, it will not be in a position to push the lens up when shifting to downgaze, so a translating design is not a good option. Fortunately, the professor’s lower lid was tangent to his lower limbus, so he was a good candidate for translating bifocal corneal GP lenses.
Evaluating Seg Height Ideally, when on the eye, the seg line will rest just below the lower pupil margin. In the professor’s case, at dispensing the seg line looked to be about 2mm below the lower pupil margin. However, when viewing the red reflex at arm’s length using an ophthalmoscope, the seg appeared to cover about half of the pupil when the professor looked down. As a final assessment, I asked the patient to keep his head in a straight-ahead position as he moved his eyes down while viewing a near acuity chart. I asked him to report when the text on the chart was clear. He did so when the chart was held at a very comfortable angle. The lenses were subsequently dispensed and continue to serve their purpose quite well to this day.
The Intermediate Distance Although translating designs offer exceptional vision and worked well in this case, some providers may be reluctant to fit translating bifocals due to the frequent need for many patients to view objects at arm’s length, such as a computer screen. This challenge can be overcome by employing a translating trifocal or a translating progressive optics design. Another option is to prescribe a pair of +1.25D spectacles to be worn over a translating bifocal design. Employing a rimless or semi-rimless frame enables the lower portion of the over-spectacle lenses to be removed, allowing patients to view near objects as usual through the near seg of their contact lenses (Figure 2).
THE NEWLY PRESBYOPIC CORNEAL GP WEARER
A 43-year-old female presented with complaints of eyestrain while performing near tasks. As a wife, a mother, a tennis player, and an English professor, she reported that her single-vision corneal GP lenses had served her needs quite well until recently. Refraction over her current lenses was plano OD and OS at distance, but a +0.75D add was needed for clear, comfortable near vision.
Contact Lens Options As the patient had worn corneal GP lenses quite successfully, it made sense to stay with this basic approach. Although a translating design was an option, I felt that a simultaneous-vision design aligned better with her active lifestyle.
Early simultaneous-vision corneal GP designs utilized high-eccentricity back surfaces to create add power. The rapid flattening of the back surface from center to edge required that the lenses be fit 4.00D to 6.00D steeper than the cornea; this often led to corneal molding resulting in spectacle blur. Newer designs have lower back-surface eccentricities, which allow for a more aligned fit. Although this reduces the likelihood of inducing corneal shape changes, spectacle blur can still be an issue with some patients.
More recently, manufacturers have been able to manipulate the front surface of GP lenses to create multifocal optics. Front-surface multifocal lenses are generally very straightforward for those individuals who are successfully wearing well-centered, single-vision GP lenses. No modification to the design of the back surface is needed. One caution: sometimes when the add is placed on the front surface, the lens thickness will increase, causing the lens to drop. This misalignment with the visual axis can lead to visual complaints. The laboratory can often remake the lenses thinner, so always check center thickness prior to dispensing to confirm that it is similar to a patient’s single-vision lenses.
For this patient, we ordered lenses with the same base curve and distance power as her single-vision lenses but with a +1.00D aspheric, center-distance add placed on the front of the lens. The multifocal lenses were only available in a 10.0mm overall diameter, but this was felt to not be significantly different from the 9.8mm overall diameter of the patient’s habitual lenses.
Troubleshooting At dispensing, the patient reported good near acuity but blurry distance vision. Loose lens over-refraction of –0.50D over the right lens and of –0.25D over the left lens provided clear 20/20 visual acuity in each eye. Both lenses rode slightly up, likely due to the larger lens size or to the differences in peripheral curve design. As the lens was a center-distance multifocal design, the superior positioning meant that the patient was viewing through an area of more plus power in the lens, explaining the need for more minus power to improve distance vision (Figure 3). As decentration was thought to be the source of the problem, the base curve of the right lens was steepened by 0.50D. An additional –0.50D was added to the contact lens distance power to compensate for the added plus power in the tear lens created by the steepened base curve.
The adjusted lenses were dispensed, but complaints of distance blur persisted. Additional minus power again resolved the distance vision complaints but reduced the near vision. We ordered new lenses with additional minus in the distance power, necessitating a need to increase the add power from +1.00D to +1.50D to maintain good near vision.
These lenses were dispensed, and the patient was quite happy with both distance and near vision, so we released her for one year.
The patient returned a few weeks later, reporting good vision with her new contact lenses but blur with her glasses. Her habitual spectacle prescription was:
OD –3.25 –1.00 x 125
OS –4.25 –1.75 x 065
Refraction immediately after contact lens removal was:
OD –4.75 –0.75 x 147
OS –6.50 –0.50 x 128
What’s going on? The patient’s visual acuity was fine with her habitual glasses prior to the refitting with her new contact lenses. Why was she having problems now? Corneal topography confirmed that the new lenses were creating corneal shape changes. But why? A front-surface multifocal design with a nearly identical back surface to her previous lenses should not alter corneal shape.
Measuring simultaneous-vision multifocal lenses can be challenging, so we looked to the invoices for an answer. We found one. With the most recent lens order, we were shipped the manufacturer’s back-surface aspheric multifocal design rather than its front-surface design. We explained this to the patient and reordered the front-surface design lenses, but after one week of wear, she returned asking for the back-surface design lenses. Although we found both pairs to provide 20/20 vision, she felt that her visual acuity was better with the back-surface aspheric lenses. It is likely that we could have improved distance vision with the front-surface aspheric lenses by enlarging the central distance zone size, but the patient didn’t want the hassle of employing this approach. So, we gave her back her preferred back-surface aspheric contact lenses and prescribed two pairs of glasses: one to wear prior to contact lens application, and one to wear after contact lens removal. The patient has functioned quite well with this arrangement for a number of years.
AN ASTIGMATIC PRESBYOPE
A spunky 50-year-old female computer specialist presented for her annual examination, expressing an interest in contact lens correction: “I’m tired of wearing glasses!” She had attempted contact lens wear in the past with other providers but was unsuccessful due to issues with both comfort and vision.
Her refraction findings were as follows:
OD –2.25 –2.50 x 004, +2.50D add, 20/20
OS plano –5.50 x 173, +2.50D add, 20/20
Her keratometry readings were as follows:
OD 43.75/46.50 @ 091
OS 43.00/47.00 @ 083
Although her visual acuity was quite good, her unusual refractive findings prompted me to look for corneal irregularity; however, topographical maps were normal (Figure 4). Recognizing the high visual demands of this patient and her challenging refractive error, I cautiously suggested that we may have success with scleral multifocal contact lenses. She enthusiastically elected to pursue this option.
Although comfort was excellent and visual acuity was reasonably good with scleral lenses, this patient had persistent problems with visual fogging after just a few hours of wear. After ruling out poor lens surface wetting and corneal edema, the fog was determined to result from an accumulation of debris in the fluid chamber between the cornea and the base curve of the lens. This phenomenon, commonly referred to as midday fogging, is known to occur with scleral lens wear and is thought to be associated with leakage of debris into the fluid chamber due to misalignment between the lens back periphery and the sclera.1,2,3 This can be detected by placing fluorescein on the front surface of a scleral lens during wear (Figure 5).You can also see two videos showing this.
Numerous attempts to seal the leak by manipulating the lens’ back peripheral toricity were unsuccessful. Improving lid hygiene and using a hydrogen peroxide disinfection system did not help. Instilling a high-viscosity, preservative-free artificial tear into the bowl of the lens at the time of lens application, which has been reported to help in such cases,4 also had very little effect.
At this point, the patient asked whether there were any soft lens options. I explained that custom toric multifocal soft contact lenses are available, but her degree of astigmatism would require the lens to be exceptionally stable to provide consistently clear vision. I shared that I doubted whether the resulting vision would be adequate enough for her to wear the lenses for work. Wearing the lenses for non-visually demanding social activities may be an option. She expressed interest in trying this lens type.
What about fees? When fitting specialty contact lenses, numerous visits can be involved. Our policy explains to patients upfront that a refund will be provided for returned materials and that any services provided are non-refundable. Due to the unusual challenge of fitting this highly astigmatic presbyope with custom toric multifocal soft contact lenses, I elected to charge the patient on a per-visit basis rather than charging a global fitting fee. Understanding the challenge, and the financial commitment involved, she elected to proceed with this approach.
Refraction, keratometric readings, and horizontal visible iris diameter (HVID) were entered into a custom soft lens manufacturer’s online calculator to arrive at the following initial base curve, diameter, and lens powers:
OD 8.1mm base curve, 14.6mm diameter, –2.25 –2.50 x 004, +2.50D add
OS 8.2mm base curve, 14.7mm diameter, plano –5.25 x 173, +2.50D add
We are generally able to dispense soft contact lenses from a diagnostic set on the day of fitting. One of the challenges in fitting custom soft lenses is the delay in delivering the lenses to the patient. To expedite the fitting process with toric soft lenses, I routinely order three lenses per eye: one on the spectacle axis and one on either side of the spectacle axis. If the on-axis lens rotates in either direction, I already have a modified axis ready to dispense, expediting the process. The question is: What axes should be ordered?
It has been proposed that 0.75D or more of residual astigmatism will result in a meaningful reduction in vision.5 Table 1 lists the amount of axis misalignment required to induce 0.75D of residual astigmatism for various toric powers.6
|TORIC LENS POWER (D)||DEGREES OF LENS ROTATION INDUCING 0.75D* OF RESIDUAL ASTIGMATISM|
For the –2.50D toric power in the right lens and the –5.25D toric power in the left lens, 9º and 4º of misalignment, respectively, results in 0.75D of residual astigmatism. Therefore, axes were ordered as follows:
OD 004 (on spectacle axis), 013 (on axis +9), and 175 (on axis –9)
OS 173 (on spectacle axis), 177 (on axis +4), and 169 (on axis –4)
Approximately two weeks later, the lenses fabricated on the spectacle axis were applied to the eyes. The patient reported: “The lenses feel good. Vision is a little blurred when going from near to distance and vice versa.” Binocular acuity was a variable 20/20 at distance and a variable 20/30 at near.
The right lens demonstrated no rotation. The left lens consistently rotated 5º to the right, so this lens was replaced with the axis 169 lens. With a 5º right rotation, this lens rested at axis 174, only 1º off of the spectacle axis.
Lenses were dispensed, and the patient was instructed to return one week later. However, the patient called the office after three days of wear and indicated that she was ready to discontinue contact lens wear.
Although unsuccessful, this patient understood from the outset that she had “challenging eyes,” and she appreciated our efforts. With the relatively recent availability of instruments to measure scleral topography, there is improved likelihood that we could achieve success with scleral lenses in the future by more precisely designing the back peripheral lens shape.
A LEFT LEANING EYE
A 47-year-old female secretary presented with complaints of blur at distance and near after recently being fit with daily disposable multifocal soft lenses. She had successfully worn a monthly replacement multifocal soft lens but was switched to a daily disposable modality to treat giant papillary conjunctivitis OD and OS.
The complaint was initially quite baffling because the patient had been refit into a daily disposable multifocal design from the same manufacturer that had made her monthly replacement lenses, and the multifocal optics were nearly identical. Further scrutiny revealed the problem. The monthly lenses had been prescribed with a high add power in the right eye and a low add power in the left eye. This had been switched when the patient was refit with the daily disposable lenses. Further testing revealed that this patient was left-eye dominant, which suggested that the patient would perform better with a low add power in the left eye. The patient performed quite well once we switched the lenses.
FINDING THE RIGHT RANGE
A 62-year-old male physician presented with interest in soft multifocal contact lenses. He had worn corneal GP multifocal lenses in the past but had discontinued wear due to dryness. He was using a foaming eyelid cleanser daily, Restasis (Allergan) OD and OS twice a day, and two omega-3 capsules by mouth per day.
Spectacle refraction was as follows:
OD –3.75 –0.25 x 170, +2.50D add, 20/20
OS –4.75 –0.75 x 100, +2.50D add, 20/20
At the completion of the refraction, I instructed the patient to view the acuity chart through the phoropter with both eyes open. I held a +1.00D power loose lens in front of one eye, then the other, and asked the patient which “bothered” him more (sensory dominance testing method). He reported that the blur was about the same in each case. So, I instructed him to hold out his hands, make an opening, and line up an object at the end of the room in the opening. With this method (sighting dominance test), the right eye was aligned with the opening, so we concluded that he was right-eye dominant.
A pair of daily disposable soft spherical multifocal lenses were fit according to the manufacturer’s recommendation. Both were high-add-power lenses. The patient reported that distance vision was good, but near vision was blurry. An over-refraction with loose lenses confirmed that the distance power in the contact lenses was correct. As both lenses already had a high add power, plus power was added to the distance power in the lens worn on the nondominant left eye. Near blur persisted.
Because the added plus power did not resolve the near blur, I suspected that the 0.75D of astigmatism in the left eye was the problem. To correct this, we dispensed a single-vision toric soft lens with the power set for near on the left eye. This provided great near vision, but now the physician complained that he was unable to see his electronic medical record charts on his computer screen at arm’s length. Reducing plus power in the left lens solved this problem, but now the patient complained of blur at the standard reading distance.
When the left lens was switched to a toric design, the range in vision provided by the multifocal was lost. To provide clear vision at both intermediate and near distances, we decided to make the nearly spherical dominant right eye the near-biased eye fit with a multifocal design. A single-vision toric lens with the power set for distance was prescribed for the nondominant left eye. Bingo. This approach met all of the patient’s visual needs.
THE VARIABLE ROLE OF DOMINANCE
These final two cases suggest that dominance is important to success with multifocal contact lenses in some cases, but it is not in other cases. To identify into which category a given patient falls, slowly introduce plus power in front of one eye, then the other while the patient views a distance object through his or her best correction with both eyes open (blur tolerance test).10 If there is a large difference in the amount of accepted plus power between the eyes, be sure to prescribe the near-biased lens for the eye that accepts more plus. If the difference is minimal, use other criteria, such as monocular astigmatism, to drive your decision-making.
RISE TO THE CHALLENGE
So many great contact lens designs are available to assist practitioners in their quest to provide patients with the many benefits of contact lens wear. I encourage you to accept the challenge and make a positive difference in the lives of your patients. CLS
- Caroline P, Andre M. Cloudy Vision with Sclerals. Contact Lens Spectrum. 2012 June;27:56.
- Miller W. Scleral contact lens fog. Contact Lens Spectrum. 2013 Sep;28:52.
- McKinney A, Miller W, Leach N, Polizzi C, van der Worp E, Bergmanson J. The Cause of Midday Visual Fogging in Scleral Gas Permeable Lens Wearers. Invest Ophthalmol Vis Sci. 2013 Jun;54 ARVO E–Abstract:5483.
- National Keratoconus Foundation. Midday Fogging with Scleral Lenses. Available at https://www.nkcf.org/midday-fogging . Accessed Aug 6, 2019.
- Quinn TG. Soft Toric Multifocals: Fix Astigmatic Correction First. Contact Lens Spectrum. 2018 Jan;33:14.
- Quinn TG, Brown WL. Fast Tracking Soft Toric Multifocal Fitting. Contact Lens Spectrum. 2018 Mar;33:16.
- Lazon de la Jara P, Papas E, Diec J, Naduvilath T, Willcox MD, Holden BA. Effect of lens care systems on the clinical performance of a contact lens. Optom Vis Sci. 2013 Apr;90:344-350.
- Chalmers RL, Keay L, McNally J, Kern J. Multicenter case-control study of the role of lens materials and care products on the development of corneal infiltrates. Optom Vis Sci. 2012 Mar;89:316-325.
- Chalmers RL, Hickson-Curran SB, Keay L, Gleason WJ, Albright R. Rates of adverse events with hydrogel and silicone hydrogel daily disposable lenses in a large postmarket surveillance registry: the TEMPO Registry. Invest Ophthalmol Vis Sci. 2015 Jan 8;56:654-663.
- Quinn TG. The Blur Tolerance Test. Contact Lens Spectrum. 2019 Mar;34:12.