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Laser refractive surgery and dry eye (TFOS DEWS II Iatrogenic Report)

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  • Laser refractive surgery and dry eye (TFOS DEWS II Iatrogenic Report)

    I see that this week marks the 30th anniversary of the first laser vision correction surgery, performed by Marguerite MacDonald.

    For those of us with dry eye and/or vision complications after elective laser vision correction procedures, this is not exactly cause for celebration.

    According to TFOS DEWS II Iatrogenic Report, which summarizes published scientific evidence of drugs, medical procedures and other medical causes of dry eye:
    • (4.4.1.1) We don't know how many people dry eye happens to after LVC, because of inconsistencies in how and when the severity is measured and because of failure to properly document the presence of dry eye before surgery.
    • (4.4.1.1) In science terms, we supposedly don't even know whether LASIK really is worse than PRK.
    • (4.4.1.1) It's possible SMILE may cause less dry eye than LASIK.
    • (4.4.1.1) Known risk factors include:
      • Low Schirmer
      • Use of MMC (used in surface ablation procedures like PRK)
      • Asian ethnicity (as with all dry eye)
      • Female sex (ditto)
      • Greater ablation depth and narrow flap hinge
    • (4.4.1.1) Most studies agree that dry eye recurs when the flap is lifted for retreatment.
    • (4.4.1.2) Ocular rosacea is a contributor.
    • (4.4.1.2) Flaps created with femtosecond lasers cause less dry eye than microkeratome flaps
    • (4.4.1.3) "Detection and treatment of dry eye prior to surgery is regarded the optimal management for refractive surgery-induced dry eye"

    These are just a few highlights. I've put in the main excerpts below. I find the coverage of LASIK in this report disappointing, but one thing it does is serve to highlight the disconnect between published medical literature and patient experience. Patient symptoms (as opposed to a far more subjective "satisfaction") need better documentation before and after surgery. Patient clinical signs need consistent measuring before surgery. - To name just a few.

    4.4 Surgically-induced DED

    4.4.1 Corneal refractive surgery

    4.4.1.1 Incidence and prevalence


    The incidence of dry eye symptoms after laser in situ keratomileusis (LASIK) surgery vary widely, depending on the severity cut-off and whether dry eye was present before surgery [204–213] In 157 eyes of 109 patients dissatisfied with LASIK, poor vision (63.1%) and dry eye (19.1%) were the chief complaints, 2.6 ± 2.8 years after surgery [207]. In a recent study, tear film dysfunction was identified as the most common reason for referral to a tertiary eye clinic following refractive surgery [214].

    There are studies suggesting that PRK induces less dry eye than LASIK [215,216], and vice versa [213,217]. Most surgeons would agree that PRK eyes tend to have more visual fluctuation at 1 month after surgery that could be related to induced dry eye [217], but that could also be attributable to prolonged central epithelial remodeling after the surface ablation procedure. Those arguing that PRK induces less dry eye than LASIK often cite damage only to the corneal nerve endings, leading to faster regeneration in PRK, but it is not clear whether there is retrograde degeneration of nerves following terminal injury in the cornea [215,216].

    Several studies have suggested that there is less change in corneal sensation and nerve density as well as less postoperative dry eye after SMILE (small incision lenticule extraction) surgery to correct refractive errors than after LASIK. [208,218–220], attributed to relative sparing of more superficial nerve fibers in SMILE. Little has been published about the effects of corneal inlays on dry eye, but the inlay acts as a barrier to regrowth of severed corneal nerves [221,222]; this suggests more dry eye should occur after inlay surgery than LASIK, but further studies are needed to explore this hypothesis.
    Risk factors for OSD or dry eye symptoms after LASIK include Schirmer test values < 10 mm [213,223,224], long-term CL wear [225], use of intraoperative mitomycin-C (MMC) [226], Asian ethnicity, female sex, a greater ablation depth as well as a narrow flap hinge [206,210,223,224,227–230]. Most studies agree that LASIK dry eye recurs after re-lifting of the flap for retreatment [231,232], but a study in Japan did not confirm this effect [233].


    4.4.1.2 Mechanism

    Most dry eye symptoms prior to refractive surgery are attributable to evaporative DED due to obstructive MGD [2,8,16]. Chronic inflammation of the lacrimal functional unit resulting in inadequate tear film integrity and function plays an important role in aqueous deficient dry eye (ADDE), which can also be associated with evaporative dry eye (EDE) [234]. Following refractive surgery, a neurotrophic component to dry eye further compromises the function of the lacrimal functional unit, at least transiently [231]. Another common contributor to dry eye symptoms and signs after refractive surgery that has received considerably less attention is ocular rosacea [216]. The tendency to reduce TBUT and the resulting evaporative component of this disease tends to worsen the symptoms and signs of dry eye after surgery and should therefore be recognized and treated prior to refractive surgery [206].

    Femtosecond laser flaps are associated with less dry eye than microkeratome flaps and studies suggest the difference is attributable to unknown factors beyond the thinner average thickness of femtosecond laser flap [216,235], hinge position or hinge angle [235]. Study results vary on whether a superior hinge position triggers less LASIK-induced dry eye than a temporal hinge position, but more recent studies using a single instrument have found no difference [235,236].


    4.4.1.3 Recommendations for management

    Detection and treatment of dry eye prior to surgery is regarded the optimal management for refractive surgery-induced dry eye [216,231,232]. Topical cyclosporine A has been found to be a highly effective treatment [237], but nonpreserved artificial tears and ointments, dietary alpha omega fatty acids, maintaining a humidity >40–50%, punctal plugs and even autologous serum drops are helpful adjuvants [237]. It is also important to treat associated conditions such as ocular rosacea (with manual compression, doxycycline, azithromycin, for example) and blepharitis (lid hygiene, antibiotics) prior to surgery. In general, treatment of dry eye should continue for at least 6–8 months following surgery and any retreatment, until the neurotrophic component reduces [238]. Many patients without symptoms or signs of dry eye will develop transient dry eye following LASIK or PRK, probably due to the neurotrophic effects of surgery [206,231,238]. Retreatment surgery is often associated with recurrence of dry eye symptoms and signs and should be preceded by optimization with cyclosporine A and nonpreserved artificial tears and ointments, with consideration of punctal plugs and autologous serum drops, depending on the severity of the disease [206,231,238].
    5.3 Areas of future [research] in surgery-induced dry eye
    Corneal hyposensitivity by corneal denervation during refractive surgery such as PRK and LASIK, which occurs by direct corneal nerve injury and following abnormal neuronal remodeling [600], has been recognized as a major risk factor for postoperative DED, although the pattern of nerve injury in the cornea differs with different types of surgery [601–604]. Recent advances in surgical procedures, including SMILE, have served to minimize corneal denervation during surgery and reduce the incidence of postoperative DED [208]. At the same time, discovery of topical medications that augment regeneration of corneal nerves after refractive surgeries to lessen the neurotrophic effects would be helpful [605–611]. Research is needed to determine whether refractive surgery can cause permanent worsening of dry eye in some patients, or whether the surgery exacerbates only underlying inflammatory dry eye, which returns to baseline when neurotrophic effects resolve with nerve regeneration [600]. Novel research is also needed into the detection of early dry eye prior to refractive surgery, so that patients with underlying dry eye are properly pretreated for dry eye to improve the outcomes of refractive surgery [612].
    Rebecca Petris
    The Dry Eye Foundation
    dryeyefoundation.org
    800-484-0244
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