REFRACTOMETRY: FINALIZE THE SPHERE ADJUSTMENT

How to approach the duochrome test

By Sue Corwin, CO, COMT

The traditional order of doing refractometry refinement is S-A-C-S: sphere, axis, cylinder, then sphere again. During the final sphere adjustment, it is important to find the most plus (or least minus) that a patient will accept to make sure the he/she is not accommodating. If the patient has to accommodate all day, it may lead to headaches, eye strain, and reduced or uncomfortable near vision. One way to check the sphere again is the duochrome test.

How it works

During this test, the patient looks at a half-red and half-green chart. Many of the modern electronic chart systems have a specific red/green chart for this purpose, but a red/green filter may be applied to a manual projector.

The examiner adds a “fog” of +0.50 D sphere on top of the prescription to relax the accommodation of the patient. Then, the examiner asks if the letters (or numbers, depending on the chart system) appear clearer and easier to see on the red side, the green side, or if they are about the same. The examiner adds minus if the patient prefers the characters on the red side and plus if the patient likes the characters on the green side. One way to remember this is “RAM GAP,” which stands for “red add minus” and “green add plus.”

Because we induced less hyperopia (or have made the patient artificially myopic) by adding +0.50 D sphere, the expected response is that the characters on the red side appear clearer. Also, we anticipate adding -0.50 D but should add only -0.75 D at the most.

Sample duochrome test

We refined the right eye S-A-C and the Rx is -2.00 +1.00 x 90. Now, we add +0.50 D to the Rx and we have -1.50 +1.00 x 90. We instruct the patient to look at the duochrome chart and ask, “On which side are the letters easier to read: the red, the green, or are they about the same?” The patient replies “the red side,” so we add -0.25 D sphere to get -1.75 +100 x 90.

Then we ask again, “Now on which side are the letters easier to read: the red, the green, or are they about the same?” The patient replies “the red side,” so we add -0.25 D sphere to get -2.00 +100 x 90.

For the last time we ask, “On which side are the letters easier to read, the red, the green, or are they about the same?” The patient replies “the same,” and we have completed the test.

THE LATEST INNOVATIONS DESIGNED TO HELP CATARACT SURGEONS CREATE A PRECISE CAPSULOTOMY

Cataract technology update

Two advances in cataract technology have recently been introduced in the United States.

Iantech’s miLoop is designed to achieve full-thickness fragmentation of the nucleus, independent of phacoemulsification energy, by using a super-elastic thin filament for endocapsular lens fragmentation. This helps surgeons achieve surgical control and efficiency mentation for any grade cataract, thus minimizing the intraocular application of ultrasonic vibrations and phaco power to the delicate ocular tissues, the company says.

miLoop is engineered to minimize capsular stress by using centripetal, out-in nucleus disassembly. Conventional techniques employ centrifugal, in-out lens cutting with adjunct phaco energy. miLoop fragmentation is done under full viscoelastic chamber stability and protection and no simultaneous irrigation and aspiration.

Another device, Mynosys’ Zepto Capsulotomy System, is a precision pulse capsulotomy device that automates the capsulorhexis procedure. Zepto uses a proprietary combination of calibrated suction and a 4-millisecond multipulse energy algorithm to produce capsulotomies. The Zepto has a disposable, round silicone suction cup with an elastic nitinol ring that sends nonthermal electrical waveform pulses to the anterior capsule for 360 degrees. This action causes a rapid phase transition of all trapped water molecules and leads to the capsulotomy effect.

Surgeons can use Zepto through a 2.2-mm incision. The capsulotomy device integrates into the standard cataract surgery routine to enhance surgical efficiency and patient flow, the company says.

miLoop and Zepto are FDA-approved devices that do not require patient shared billing.

CLARIFICATION

In the “Coding update for 2018” article in our January/February 2018 issue, two CPT codes were incorrectly labeled. The new CPT code 0449T (Insertion of anterior segment drainage device w/o extraocular reservoir, internal, to subconjunctival space) applies to the XEN Gel Stent. The new CPT code 0474T (Insertion of anterior segment drainage device w/ creation of extraocular reservoir, internal, to supraciliary space) applies to the CyPass Stent. The editors of Ophthalmic Professional apologize for this oversight.