KAMRA Inlay Refractive Program at Vance Thompson Vision
KAMRA Top Line
The KAMRA inlay is performed in the non-dominant eye.
The KAMRA inlay is inserted into a pocket made by a femtosecond laser within the corneal stroma (approximately 200 - 250 microns deep).
The KAMRA inlay is a 3.8 mm opaque disc with a 1.6 mm aperature. The advantage of this small aperature is that is increases depth of focus. So, it doesn't blur distance as much as a mono-vision can and it still provides good intermediate and near vision.
Since the KAMRA inlay increases depth of focus, it can make a refraction more challenging (See mid-point refraction section).
The KAMRA inlay is removeable if BCVA would ever be reduced or if we were to ever see any corneal haze.
There is a long taper of steroids to decrease risk of corneal haze (Pred-moxi qid x 1 week, FML qid x3 weeks, FML tid x 1 month, FML bid x 1 month).
Tear film management is critical for success. It is recommended to put permanent punctal plugs in the lower lid and 90 day plugs in the upper lid.
The KAMRA inlay can be repositioned if centration were ever an issue.
The KAMRA inlay can be done on patients who have had previous LASIK (as long as they have at least 500 microns of central corneal tissue).
We can perform PRK over the KAMRA inlay if refractive error needs adjustment.
The KAMRA inlay can remain in the cornea if a patient were to need cataract surgery.
A Yag laser capsulotomy can be performed with a KAMRA inlay in the cornea.
What is the Procedure?
Vance Thompson Vision had the honor of being on of the first in the United States to perform the KAMRA Corneal Inlay for the treatment of presbyopia. To date, the KAMRA is the only FDA approved presbyopia procedure utilizing small aperature optics.
The KAMRA is a small, opaque, 6 micron thin (a red blood cell is 7 microns) polymer material that is placed within the cirneal stroma of the non-dominant eye. At just 3.8 mm in diameter, the inlay is circular (resmbling the pupil), and has a small 1.6 mm aperature in the center, which is placed over the pupil of the eye. This small sperature creates an increased depth of focus which provides clear vision at all distances.
When and Why Do It?
- Age: Between 45 and 60 years of age
- Spherical Equivalent: between +0.50 and -0.75
- Astigmatism: less than or equal to 0.75
- Stable refraction for a minimum of 1 year
- Pachymetry > 500 microns
- Mesopic pupil size less than or equal to 6.0 mm
- Severe dry eye
- Macular Degeneration
- Corneal dystrophy or degeneration
- Amblyopia or Strabisms
- Visual Acuity
- Dry and Cyloplegic Refraction
- Eye Dominance
- Cover Test
- AcuTarget HD
- Slit Lamp Exam
- Mesopic Pupil Size
- Corneal Diameter (WTW)
- Dry Eye Assessment
- Posterior Segment
How is the Procedure Done?
The KAMRA inlay procedure is divided into two stages: making the pocker and inserting the inlay. The actual procedure take approximately 10 minutes. We use a topical anesthetic to numb the eye and offer Valium to help calm people's nerves. A lid speculum is place to cotrol blinking and provide adequate corneal exposure.
One thing we really like about this procedure is that it is very similar to making a LASIK flap. A pocket is created within the stroma, using our femtosecond laser, at a depth of 200 - 250 microns. Then the inlay is inserted into the pocket. The KAMRA inlay is removeable.
Proper placement of the inlay is an important factor in achieving good outcomes and effectiveness. We use the Acutarget HD instrument, which gives us a Purkinje and Pupil cord length. These measurements have helped greatly in achieving ideal centration of the device.
Dry eye can affect the quaity of vision with the inay. So, we aggressively treat the ocular surface with plugs (permanent lower lid and 90 day upper lid) and restasis.
Corneal haze can be another side effect of the inlay. To lessen the risk, we do a long taper with a steroid.
Decreased BCVA can e a result of a decentered inlay (assuming dry eye has been treated and there is no corneal haze). The best way to check the centration of the inlay is with the AcuTarget HD (See Figure 3.)
Day of surgery: We well our patients that their vision will be blurry the day of their surgery. We also tell them to expect 2 - 6 hours of some discomfort immediately following surgery. This discomfort can range from mild, foreign body sensation, to severe burning, watering, photophobia and stinging. Regardless of the type of discomfort, it will typically only last 2 - 6 hours.
It is normal for the patient's vision to be blurry for the first week or two, followed by a slow visual recovery for the next 3 to 6 months. Educating our patients on this long visual recovery is very important.
- Pred/Gati qid x 1 week, FML qid x 3 weeks, FML tid x 1 month, FML bid x 1 month.
- Restasis bid if patient has dry eyes.
- Non-preserved artificial tears as needed.
Follow Up Visits
1 day, 1 week, 1, 3, 6 months and 1 year
Recommended Tests include: UCVA, BVCA, near point add, Mid-point refraction, Slit lamp exam, Dry eye evaluaiton, IOP, Topography, AcuTarget HD
Due to the small apeture design, refractions can be more challenging in the implanted eye. The refractive end points are usually softer as the patient is able to tolerate a larger range of lenses witour experienceing blur. Again, this is due to the increased depth of focus that the KAMRA inlay provides.
- Perform a normal manifest refraction, the instruct patient to fixate on a line that's 2 lines above the BCVA.
- Add plus lenses until first blur, record their endpoint
- Starting from baseline manifest refraction, now add minu
- s until first blur, record endpoint.
- Calculate the mid-point refraction using the following equation:
[(Endpoint plus blur) + (Endpoint minus blur)] / 2 = (rounded to the nearest max plus 0.25D)
- Initial MRx: +1.00 - 0.75x090
- Plus lenses to blur + 0.50 (2 lenses)
- Minus lenses to blur -1.75 (7 lenses)
- [(+0.50) + (-1.75)] / 2 = -0.62 D (rounded to -0.50 D)
- -0.50 + 1.00 = +0.50
Final midpoint refraction: +0.50-0.75x090
Side Effects & Post-Op Complaints
Post-operative complications can include, infection, slowed or non-healing epithelial defects, persistent epithelial ridge formation, steroid response, under and over-correction, anterior reticular haze, and recurrent erosion.
Infection rates with PRK are extremely low, but, with the large epithelial defects that we are dealing with, patients must be monitored closely and treated aggressively to prevent loss of vision or corneal scar formation from a virulent infection. Any infiltrate noted during healing should be brought to our attention and referred in for evaluation.
As we talked about in the previous section, if slowed or non-progressive epithelial healing is determined, we increase lubrication and decrease anti-inflammatory medication to promote epithelial healing. Using this medication protocol along with continued bandage contact lenses will usually promote epithelial healing and the defect should seal within several days. If the epithelium is still not sealed after 6 days, the patient should be scheduled back with us at the refractive surgery center for evaluation and treatment.
Commonly, a central epithelial ridge will form where the epithelial edges seal together. This ridge usually smoothens itself out over the first 2 to 4 weeks postoperatively. If the ridge persists and is blurring vision at 4 weeks post-op, we discuss with the patient that we may need to mechanically remove the aberrant epithelium to grow smoother and more viable epithelium. A persistent epithelial ridge could lead to an elevated central island of tissue and cause significant visual problems.
Some believe steroid use following PRK is important to help reduce the potential for aggressive healing and corneal haze formation. The smoother ablation patterns of advanced lasers and intra-operative treatment with anti-metabolites have helped reduce the risk of haze. Therefore, our current impression is that patients do not need extended steroid treatment in order to reduce the chance of haze. Since we recommend discontinuing steroid use after 2 weeks, steroid responders with elevated IOP should be very rare. We recommend waiting at least 2 weeks before performing applanation tonometry (unless you are noting signs of elevated IOP), to help reduce the risk of damaging the healing epithelium.
As with all refractive procedures, over and under-corrections can occur. All patients are counseled on the importance of waiting at least six months for healing and refractive stability before considering an enhancement. Remodeling of the epithelium can be very powerful in improving uncorrected visual acuity and decreasing residual refractive error, so being patient with PRK healing is important.
As mentioned earlier, Central corneal haze with PRK is not as prevalent as in the past, due to the smoother ablation patterns of advanced lasers, better patient selection, use of anti-metabolites during surgery, and controlled steroid use. Even so, anterior reticular haze can occur after PRK. Small amounts (Trace haze, Figure 1) of anterior haze are very normal with PRK, and usually do not affect vision or BCVA. This haze typically develops at around 1 month postoperatively and peaks at 3 months. After 3 months, the haze begins to diminish and returns to pre-operative levels within 6 to 18 months. This early haze, which does not affect acuity or image quality, used to be concerning to clinicians. It is now recognized as a normal healing reaction following PRK.
More aggressive healing reactions producing 1+ (Figure 2: 1+ Haze) to 2+ haze (Figure 3: 2+Haze) are rare, but require treatment. If more than trace haze is noted, we recommend referring the patient back to Vance Thompson Vision for evaluation and potential surgical treatment to reduce haze. We know there are several factors that can contribute to the formation of haze. Significant UV exposure is one factor that some believe increases the risk of visually significant haze. We recommend UV protection (sunglasses) for PRK patients for at least 6 months following the procedure.
Recurrent erosion is rare with PRK as it has been demonstrated that epithelial adherence to the laser ablated corneal stroma is stronger than it was pre-laser. This is why PTK has such a strong therapeutic effect on patients with anterior basement membrane dystrophy and recurrent erosion. Rarely, recurrent erosions can occur at the edge of the PRK treatment zone and can be treated with additional therapeutic laser treatment.
Maximizing Patient Outcomes
There are three primary components to maximizing patient outcomes: Pre-operative examination, Intra-operative technology and experience and Post-operative management.
Before surgery: Patient selection during the the pre-operative exam is critial. Ideally, we are looking for presbyopes with refractive error around +0.50 to -0.75 with less than -0.75 of astigmatism. Corneal thickness nees to be greater than 500 microns.
Managing patient expectations and aggressively treating the tear film will aid in successful outcomes.
During surgery: It is imperative to make sure the inlay is centered.
After surgery: It's important to emphasize the length of time it takes for the vision to completely recover and continue to aggressively treat the tear film.