GP Lens Case Grand Rounds Troubleshooting Guide

Intermediate Presbyopia (Previous Soft or Monovision Wearer): Robert L. Davis, OD, FAAO

Background

AJ is personal secretary to a high profile restaurateur who manages dozens of restaurants in Chicago, Las Vegas, Phoenix, Los Angles, Seattle and Minneapolis. Her daily routine creates a demand on her visual system to be able to perform at a variety of working distances. This 50-year-old personal manager requires a visual device that is both comfortable and optically pristine. She has been wearing monovision soft toric lenses for two years accepting the visual compromises that soft lenses and monovision delivers.

At her yearly annual examination AJ complained that her vision was not adequate to perform at distance and near. Driving at night was difficult and the volumes of reading material became tiresome after a short period of time. When she was not at work during daily routines the vision seemed to be tolerable. AJ asked if another contact lens type would improve her vision compared to her soft toric monovision lens design.

Test Procedures, Fitting/Refitting, Design and Ordering

Entrance Visual Acuity with Current Spectacles at Distance:

Uncorrected Visual Acuity at Distance:

OD: 20/300
OS: 20/300
OU: 20/200

Previous Contact Lens Specifications:

Manifest Refraction at Distance and Near:

Keratometry (sim Ks):

Intraocular Pressure:

OD: 14 mmHg
OS: 18 mmHg

Pupillary responses were equal, round and reactive to light and accommodation with no afferent pupillary defect. In normal room illumination, pupil size was 3.6 mm OD and 3.8 OS mm as measured with the Neuroptic Pupilometer. In dim illumination pupil size was 4.8 mm OD and 5.2 mm OS. Versions were smooth and full OU.

Slit Lamp Evaluation (without Lenses):

Upon lid eversion the tarsal conjunctiva exhibited a smooth satin appearance. The inferior tear meniscus appeared to be clear and adequate in height to support contact lens wear. The Tear Break-Up-Time was 17 seconds OD and 19 seconds OS. The Meibomian glands excreted clear fluid upon gentle expression. No corneal staining was evident with fluorescein application. Lower lid was 1mm below the limbus.

After the examination AJ was given options to solve her visual acuity problems. I wanted to bring her into the decision making process so she would understand the options and give input which is extremely helpful during the follow-up appointment discussions. We discussed to increase the monovision effect with soft toric lenses or GP lenses by reducing the left lens prescription which would give her improved near vision although would reduce the quality of the distance vision. I told her that the snellen acuity distant line on the chart would not change although it would not be as sharp or crisp with monovision.

AJ was given another option to prescribe a full distance prescription with soft toric lenses or GP lenses and use reading glasses over the contact lenses. This would improve distance vision although a pair of reading glasses would be necessary with near or intermediate vision. My experience is that this is very frustrating and inconvenient.

The third option given to AJ was to use a GP bifocal contact lens design that would provide pristine distant vision and effortless intermediate and reading acuity. Adapting to the rigid GP lens requires less time than adapting to a bifocal spectacle prescription. The fitting characteristic of the rigid lens gives a much larger near bifocal window as compared to spectacle lenses. Viewing the near power of the GP bifocal is manipulated by the angle below the horizontal. The bifocal contact lens near add power is controlled by the axis of the visual demand. The near power increases as the visual direction angles below the level chin orientation.

The spectacle prescription is fixed and does not move with the eye. This creates difficulties with the spectacle design when walking down steps or looking down in a sports arena. The simultaneous contact lens bifocal lens design is seamless because the visual system does not know where the bifocal lens power exists. We discussed all the options and decided together to proceed with the GP bifocal lens fitting.

Fitting/Troubleshooting:

I first wanted AJ to experience rigid gas permeable lenses on the eye to understand the comfort and quality of vision difference between GP and soft lenses. I selected an Aspheric Tangent Streak No-Line (Fused Kontacts of Missouri) 7.70mm base curve radius for the right eye and a backside annular Decarle Bifocal Icon 4 7.70mm base curve radius for the left eye from my trial lens set. Her initial reaction was that both lenses felt considerably more uncomfortable than the soft toric lenses although it was tolerable.

Both lenses centered well although the visual results of the DeCarle backside annular design did not give AJ the intermediate vision range needed to perform her work as compared to the Aspheric Tangent Streak. The Decarle bifocal has a centered distance zone and an annular reading zone of one power on the backside of the lens.

The Aspheric No-Line Tangent Streak is a progressive aspheric design where the bifocal zone progressively increases as the position moves away from the center of the lens. This lens designs offers multiple focal points as the eye positions below the straight ahead position. The lens fitting base curve is fit .16 steeper than the real base curve to generate sufficient addition power. The fitting base curve is approximately one diopter steeper than the real base curve.

Lens Specifications

Slit Lamp Evaluation (with Contact Lenses):

Observing the lens through the biomicroscope exhibited good vertical movement and central positioning in straight-a-head gaze. The no-line Tangent streak needs to position slightly superior to central to provide good translation upon downward gaze. The add power needs to position into the pupil area as the eye moves below the horizontal orientation. If the lens needs to be position more superiorly than a flatter base curve would be selected.

Both lenses were perceived as comfortable by the patient after one drop of anesthetic was instilled. The anesthetic was instilled to get a realistic observation of lens movement without the additional tearing by an unadapted patient and to increase the comfort after the initial genuine sensation of a GP lens. An over-refraction was performed and loose trial lenses were place over each eye to test the distant, intermediate and near vision out of the phoropter. If additional near prescription would be required, +0.50D could be put in an annular configuration on the front of the lens.

A discussion was held with the patient explaining the operation of the bifocal. The straightahead position was configured for distance vision and, as you look through a lower position of the lens vertically, the near power is increased in the lens which corresponds to a closer reading position. The patient was instructed that the intermediate or computer power could be aligned slightly below the horizontal and the reading prescription was further below the horizontal.

Fluorescein was instilled to observe the lens-to-cornea fitting relationship. Both lenses revealed a slightly apical clearance fitting relationship with slight bearing in the periphery. AJ was satisfied that this lens design would accomplish all the visual tasks needed in her profession and the lenses were ordered.

Patient Consultation and Education

Dispensing Visit:

AJ returned to the office for her dispensing visit approximately a week later. Lenses were applied to her eyes by the assistant after an instillation of one drop of anesthetic. The anesthetic was instilled to promote the positive management during the education process of lens application, removal, disinfection and lens orientation. Boston solutions were dispensed with both Miraflow surfactant and an enzymatic cleaner. The wearing schedule was discussed with AJ to start with four hours and increase two hours each day. Visual acuity testing and slit lamp was performed to guarantee that the lens ordered performed as the fitting visit. An appointment was scheduled for one week.

Tangent Streak No-Line Gas Permeable Multifocal:

Lens Specifications

Follow-Up Care/Final Outcome

One Week After Lens Dispensing:

AJ returned for her follow-up appointment eight days after the dispensing visit. She was happy with the visual acuity and the range of the Tangent Streak No-Line progressive lens. AJ commented that the lens comfort was improving with increase wearing time. The one problem that AJ experienced was that her glasses did not perform the same after she started wearing the new lens design.

Manifest Refraction at Distance and Near:

Keratometry (sim Ks):

OD: 42.87 @ 180; 44.87 @ 090 (corneal molding)
OS: 42.75 @ 180; 44.50 @ 090 (corneal molding)

Slit Lamp Evaluation (with Contact Lenses):

With biomicroscopy, a slight apical clearance fluorescein pattern was present. The periphery revealed pooling and exhibited good edge lift and pumping action. The paracentral area demonstrated bearing and the lenses both displayed central positioning with good lens movement.

Corneal molding was explained to AJ. “The lens design is constructed to flatten the cornea to generate the reading power. The minus prescription of the eye is temporarily reduced when the cornea is flattened by the lens design. The previous spectacle prescription will no longer perform adequately after the removal of the progressive lens design. The cornea will slowly go back to the original prescription in time. Similarly when you take off your ring there is an impression where the ring changes the shape of the finger. It does not harm the finger and eventually the finger will go back to its original shape. This is the reason that the vision through the glasses improves in the morning after no lens wear over night.”

In order to arrive at an optimal prescription AJ needed to determine if the glasses will be worn more often in the morning before lens wear or in the evening after lens wear. If this arrangement is not acceptable to AJ then she was told that a new design would have to be implemented. The new lens design would not allow for the range of vision that the Tangent Streak No-Line lens offers. AJ decided that the present lens design was optimal for her visual requirements. After our discussion it was decided that her present glasses would be used only for morning wear and a new prescription would be fabricated for evening wear. A follow-up appointment was scheduled for two weeks in the morning to refract a new prescription.

Third Week After Lens Dispensing:

AJ came into the office wearing contact lenses for an early evening refraction to purchase a pair of glasses after contact lens wear. She explained that the spectacles would come in handy after removing her contact lenses after a long day of work to rest her eyes. The old pair of glasses she was not going to change because they could be used on Sunday mornings when she does not normally wear contact lenses until the afternoon.

Manifest Refraction at Distance and Near:

Keratometry (sim Ks):

OD: 43.00 @180; 45.12 @ 090
OD: 43.00 @ 180 44.87 @ 090

Discussion, Alternative Management Options

This case demonstrates the management and fitting of a progressive aspheric bifocal contact lens. The first bifocal for a presbyope has many lens design options in solving the problematic near visual acuity. Discussing the patient’s visual requirements will help determine the best bifocal lens design. The advantages of the aspheric simultaneous vision design include the improved visual range for near point activities, comfort similar to the spherical GP lens and the pristine distance acuity. The progressive contact lens strategy offers the practitioner many fitting options to modify the lens design to arrive at a successful outcome. The major drawback is the corneal molding imparted by the aspheric progressive lens design.

The lens positioning needs to be configured to reside in front of the pupil. Flatter lenses will create an upward positioning. Steeper lenses will create a downward positioning. Additional add power can be placed in a spherical annular configuration on the front of the lens to increase the total add power. Pupil size is also an important parameter to consider during the fitting process. Large pupils under scotopic conditions will increase the effects of flare, glare or halos. Pupil size can affect the quality of the distance acuity when the vision from the add powers is allowed to project onto the retina.

The pupil serves two purposes in fitting bifocal lens designs. The first is to allow sufficient focused images to fall upon the retina for good translation from distance to near viewing. The second is to limit the amount of defocused images to fall upon the retina. The control of this balance is the key to bifocal lens design success.

As the back surface aspheric bifocal add power increases the lens designs requires a steeper fitting curve. Crowding the add prescription is necessary in the near zone space to generate a stronger near prescription as compared to lower add prescriptions. Optical confusion is produced by crowding the prescriptions in the near zone space. In low aspheric bifocal designs the graduated near prescriptions are more spread out. In higher eccentric lens designs in order to get the graduated higher add in the same space, the near powers are crowded more closely together.

Successful patient management is dependent on the communication skills of the practitioner to describe the lens design. Each follow-up appointment will determine the difficulties that need to be solved to reach a successful conclusion. It is difficult at best to predict every possible environment that the bifocal lens designs need to perform optimally for the patient. Translating the patient’s complaints and descriptions to modifying the lens design and/or fitting parameters will ultimately guide the practitioner. The knowledge and understanding of patient management, bifocal lens designs and modifications necessary to satisfy the patient’s visual needs formulate the contact lens specialist.

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