Management of Cystoid Macular Edema Secondary to Retinitis Pigmentosa Via Subliminal Micropulse Yellow Laser
Condition: Retinitis Pigmentosa; Cystoid Macular Edema
MeSH terms: Macular Edema; Retinitis; Retinitis Pigmentosa; Edema
Study type: Interventional

Summary: 
      Purpose: To investigate the effects of subliminal micropulse yellow laser application on
      central macular thickness and best corrected visual acuity in cystoid macular edema secondary
      to retinitis pigmentosa patients.
    

Detailed description: 
      Retinitis pigmentosa (RP) is a progressive photoreceptor and retinal pigment epithelial (RPE)
      degeneration that begins as a night vision loss, resulting in narrowing of the visual field
      and legal blindness. RP is a heterogeneous genetic disorder, affecting 1/3000- 8000 people
      worldwide. RP is the result of mutation in one of more than 260 genes. These genes are
      responsible for the synthesis of peptides involved in the visual cycle. These genes are also
      responsible for the synthesis of growth factors responsible for the conversion of glucose to
      adenosine triphosphate (ATP) or responsible for the removal of metabolic wastes.

      The incidence of cystoid macular edema (CME) in RP has been reported as between 10% - 50%.
      There are several hypotheses about the pathogenesis of cystoid macular edema in RP. The first
      hypothesis is explained by Müller cell hypertrophy and its paracrine effects. Mutations in
      the retinal pigment epithelium disrupt the synthesis of some growth factors. Stress caused by
      apoptosis in rod cells in the periphery leads to ectopic synaptogenesis of Müller cells in
      the central. Müller cells undergo copensatory hypertrophy and synthesize excessive growth
      factors. This paracrine effect provides protection of central vision. Edema in a certain
      level is considered to be protective to photoreceptors and should not be treated. But if
      edema is excessive and prolonged leads to a break in synaptic connections in the neural
      retina and an increase in neurodegeneration. CME also deteriorates central visual quality in
      patients with impaired peripheral vision. Treatment should be considered only if the edema is
      excessive and disrupts central vision. According to our clinical experience, when central
      macular thickness exceeds 500 microns, central visual quality of the patient decreases and
      requires treatment.

      Other pathophysiological causes of CME in RP are explained by low grade inflammation and
      retinal autoantibodies. In some genetic mutation types of RP, such as the X-linked RPGR gene
      mutation; vitritis, lipofuscin deposits and inflammation are predominant. Ciliopathy leads to
      inflammation and CME, which increases photoreceptor loss rate. Immediate treatment of
      inflammation-induced edema can slow disease progression. Inflammatory edema appears as
      cystoid macular edema, whereas compensatory edema due to Müller cell hypertrophy is seen as
      separeted intraretinal cysts. Inflammatory edema responds well to carbonic anhydrase
      inhibitors, while compensatory edema does not.

      The results of the treatment of CME in RP are controversial, as the compensatory or
      inflammatory distinction is not made clearly. Treatments such as grid laser photocoagulation,
      oral acetazolamide, topical carbonic anhydrase inhibitors, intravitreal therapy with
      corticosteroids or anti-vascular endothelial growth factor agents and pars plana vitrectomy
      may be effective in some cases with CME secondary to RP. Most of these treatments have either
      insufficient response or excessive side effects.

      To our knowledge, so far, we have not found a scientific publication about the use of
      micropulse yellow laser for treatment cystoid macular edema secondary to retinitis
      pigmentosa.

      Subliminal micropulse laser (SL-MPL) is a method developed to reduce the laser-induced
      thermal damage caused by conventional laser therapy for treatment some macular diseases. In
      the micropulse mode, laser is applied in short pulses, thereby reducing the thermal energy
      generated in the target area. The coagulation scars do not form with SL-MPL treatment.
      Sublethally injured RPE cells induce an up- and down regulation of various growth factors
      (GFs) [pigment epithelium-derived factor (PEDF), vascular endothelial growth factor (VEGF)
      inhibitors, VEGF inducers, permeability factors, etc.] which restores the pathologic
      imbalance.

      The aim of this study was to investigate the effect of yellow (577 nm) SL-MPL therapy on
      central macular thickness (CMT) and on best corrected visual acuity (BCVA) in patients with
      cystoid macular edema secondary to retinitis pigmentosa.
    

Intervention name(s): SL-MPL treatment protocol was performed with a 577 nm yellow laser (EasyRet, Quantel Medical, Cedex, France)
Intervention type(s): Device
Intervention description(s): Macular laser treatment was applied after pupil dilation and topical anesthesia. Laser application was performed with a Mainster Standard contact laser lens (Volk Optical, Mentor, OH, USA). To determine the appropriate personalized calibration value, single-spot test shot was applied under the green filter to a non-edematous area of the macula outside the temporal vascular arcade. The laser power was gradually increased until it formed a barely visible laser spot. The power of the micropulse pattern laser was set at 50% of the power needed to form a barely visible laser spot. Laser parameters used were 200 ms duration, 160 µm spot diameter, low operating cycle (5%), and zero spacing with 5x5 pattern shape. SL-MPL was applied to the areas where edema was detected in OCT and examination.
Allocation: Non-Randomized
Intervention model: Single Group Assignment
Intervention model description: Prospective open-label clinical trial, included 32 eyes of 29 patients who had cystoid macular edema secondary to retinitis pigmentosa. Patients were treated by subliminal micropulse yellow laser for one session. Central macular thickness and best corrected visual acuity changes were investigated just before the treatment and 1 year later after the one session of the treatment.
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Retinitis pigmentosa; Cystoid macular edema; Intraretinal cysts; Subliminal micropulse laser