Article

Kamra: A review

The Kamra inlay (AcuFocus, Inc.) was the first corneal inlay to receive both U.S. FDA approval1 and the CE Mark. Its diameter is 3.8 mm, with a central aperture measuring 1.6 mm.2 This design increases the implanted eye’s depth of focus by utilizing the pinhole optical principle. It is made from polyvinylidene fluoride, an enhanced biomaterial that allows a light transmission of 6.7%.3 Adequate fluid and nutrient flow is permitted through the Kamra due to its 5-μm thickness and with its 8,400 laser-etched microperforated holes arranged in a pseudorandom pattern.4

Kamra is approved in more than 50 other countries, with an estimated 20,000 implanted worldwide.5 The latest Kamra model (ACI7000PDT) is 5-μm thick and, compared to older models, has an increase of microperforations to 8,400 (up from 1,600), fewer corneal topography changes and improvements to visual acuity.6

The Kamra inlay is indicated for implantation in the nondominant eye of patients who are between the ages of 45 and 60. Its IDE trial enrolled 508 eyes with a 36-month follow-up plan that was extended to 60 months in a continuation study. After the continuation study, 87.1% of the eyes involved had an UNVA of 20/40 or better.7

The most optimal refractive outcomes occur when the nondominant eyes have a small amount of residual myopia (-0.75 D to -1.00 D) with less than 0.75 D of astigmatism and there is plano refraction in the dominant eye.

INDICATIONS AND SELECTION

The Kamra inlay ideally improves both near and intermediate visual acuity. Increased depth of focus occurs because the small aperture does not produce any splitting of light between the near, intermediate and distance focal points. The sufficient binocular input with the Kamra does not cause any significant decreases in stereoacuity.8,9

The Kamra should be implanted in a femtosecond laser stromal pocket at a depth of around 220 μm,6 except in cases where LASIK has been performed. These cases employ a dual interface technique, with the implant placed about 100 to 110 μm beneath the flap.10

The Kamra inlay has been effectively used in naturally emmetropic patients, post-LASIK emmetropic patients, with LASIK correction as a simultaneous or two-step sequential procedure, and in pseudophakic patients with a monofocal or phakic intraocular lens.4

NEW DATA

In a 2017 small case series, seven patients who had Kamra inlays were assessed before and after their cataract surgeries. Five had 20/20 UDVA; all seven had 20/25. The surgeons found the IOL biometry calculations were correct, and they did not need to change surgical technique.11

In 2015, Tomita and Waring published results on 277 hyperopic presbyopic patients with astigmatism, divided by age, showing that simultaneous implant of Kamra and LASIK surgery was effective and safe; all groups had a UDVA of 20/20. Group 3, with the oldest patients, had the largest vision gains and were the most satisfied. The study noted age could be a consideration in helping reach the best postoperative outcomes.12

Another recent study found further evidence that a patient’s level of stereoacuity before and after inlay surgery is essentially the same.13

SAFETY QUESTIONS

While studies have documented the safety of the Kamra inlay, it is susceptible to the same standard risks and complications as refractive surgery.10 Adverse outcome risks are associated with the healing response, with possible hyperopic shifts occurring due to stromal thickening over the inlay.10 Also reported are corneal haze, epithelial iron deposition and infectious keratitis.14,15 The most common problems were dryness (28%), blurry/fluctuating vision (22%) and night vision problems (19%). Unwanted outcomes can be addressed by removal of the inlay. There could be an associated shift in the implanted eye’s refraction, but the final corrected visual acuity was not shown to change from pre-operative measurements.2 OM

REFERENCES

  1. US Food and Drug Administration. FDA approves first-of-its-kind corneal implant to improve near vision in certain patients. https://www.fda.gov/newsevents/newsroom/pressannouncements/ucm443471.htm . Accessed September 16, 2017.
  2. Yilmaz ÖF, Bayraktar S, Agca A, et al. Intracorneal inlay for the surgical correction of presbyopia. J Cataract Refract Surg. 2008;34:1921-1927.
  3. Arlt E, Krall E, Moussa S, Grabner G, Dexl A. Implantable inlay devices for presbyopia: the evidence to date. Clin Ophthalmol. 2015;9:129-137.
  4. Moarefi MA, Bafna S, Wiley W. A Review of Presbyopia Treatment with Corneal Inlays. Ophthalmol Ther. 2017;6:55-65.
  5. Lindstrom RL, Macrae SM, Pepose JS, Hoopes PC Sr. Corneal inlays for presbyopia correction. Curr Opin Ophthalmol. 2013;24:281-287.
  6. Naroo SA, Bilkhu PS. Clinical utility of the Kamra corneal inlay. Clin Ophthalmol. 2016;10:913-919.
  7. Kamra [professional use information]. www.accessdata.fda.gov/cdrh_docs/pdf12/p120023d.pdf . Accessed September 16, 2017.
  8. Linn S, Hoopes PC. Stereopsis In Patients Implanted with a Small Aperture Corneal Inlay. Invest Ophthalmol Vis Sci. 2012;53:1392.
  9. Dexl AK, Seyeddain O, Riha W, et al. One-year visual outcomes and patient satisfaction after surgical correction of presbyopia with an intracorneal inlay of a new design. J Cataract Refract Surg. 2012;38:262-269.
  10. Greenwood M, Bafna S, Thompson V. Surgical Correction of Presbyopia: Lenticular, Corneal, and Scleral Approaches. Int Ophthalmol Clin. 2016;56:149-166.
  11. Moshirfar M, Quist TS, et al. Cataract surgery in patients with a previous history of kamra inlay implantation: a case series. Ophthalmol Ther. 2017 Jun;6(1):207-213.
  12. Tomita M, Waring GO 4th. One-year results of simultaneous laser in situ keratomileusis and small-aperture corneal inlay implantation for hyperopic presbyopia: comparison by age. J Cataract Refract Surg. 2015 Jan;41(1):152-61.
  13. Linn SH, Skanchy DF, Quist TS, Desautels JD, Moshirfar M. Stereoacuity after small aperture corneal inlay implantation. Clin Ophthalmol. 2017 Jan 24;11:233-235.
  14. Duignan ES, Farrell S, Treacy MP, et al. Corneal inlay implantation complicated by infectious keratitis. Br J Ophthalmol. 2016;100(2):269-273.
  15. Dexl AK, Jell G, Strohmaier C, et al. Long-term outcomes after monocular corneal inlay implantation for the surgical compensation of presbyopia. J Cataract Refract Surg. 2015;41:566-575.

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