Prospective Evaluation of the Efficacy of Pascal Laser Iridotomy and Pascal Laser Peripheral Iridoplasty: A Pilot Study
Condition: Glaucoma
MeSH terms: Glaucoma
Study type: Interventional

Summary: 
      Objective: The main objective of this study is to evaluate the efficacy of Pascal Laser
      Iridotomy and Pascal Laser Peripheral Iridoplasty in lowering intraocular pressure and
      opening up the angles in patients with narrow angles, primary angle closure and primary angle
      closure glaucoma.

      The specific objectives are to evaluate the pain and inflammation associated with the
      procedure and its possible adverse effects on the lens and corneal endothelium.

      Study Design: Prospective, interventional case series Study Population: Healthy males and
      females with appositional angle closure aged 21 y/o and above Methods: Potential participants
      are evaluated by a glaucoma specialist in National University Hospital. If they are
      identified as having appositional angle closure they are invited to participate in the study
      and assigned to either iridotomy or iridoplasty depending on the mechanism of angle closure
      present. Pupil block for Pascal Laser Iridotomy and plateau iris and angle crowding for
      Pascal Laser Peripheral Iridoplasty. If they agree to participate they will undergo visual
      acuity, slit lamp examination, intraocular pressure determination by Goldmann Applanation
      Tonometry, gonioscopy, optic nerve head evaluation by indirect ophthalmoscopy and lens
      evaluation by LOCS III opacity grading system. Humphrey visual field examination using 24-2
      SITA standard algorithm and stereodisc photos will be obtained if not done within the past 12
      months. Anterior segment OCT and laser flare meter will also be performed prior to the
      procedure. Enrolled patients will be divided into 2 groups. The first group will be assigned
      to Pascal Laser Iridotomy. The primary mechanism of angle closure in this group is pupillary
      block. The second group will be assigned to Pascal Laser Peripheral Iridoplasty. This group
      has non-pupil bock mechanisms which include plateau iris or angle crowding. After the laser
      procedure, follow-up examinations will be done 1 hr post laser, 1 week, 1 month, 3 months and
      6 months.

      Outcome Measures: The primary outcome measures are the intraocular pressure difference pre
      and post laser and the opening of angles. Secondary outcome measures are pain and
      inflammation associated with laser procedure, lens and corneal endothelial changes.
    

Detailed description: 
      PLANNED INTERVENTIONS Potential study participants are seen by a glaucoma specialist at
      National University Hospital. If they are identified as having primary angle closure and have
      met the inclusion criteria mentioned above, they will be invited to participate in the study.
      Potential risks and benefits will be explained. After which, they will sign an informed
      consent when they agree to participate.

      Visual acuity, slit lamp examination, intraocular pressure determination through Goldmann
      Applanation Tonometry, gonioscopy, optic nerve head examination through indirect
      ophthalmoscopy and lens evaluation using LOCS III lens opacity grading system will be done on
      baseline visit. Humphrey visual field exam using 24-2, SITA standard algorithm and stereodisc
      photos will also be obtained if not done within the past 12 months. Anterior segment OCT,
      laser flare meter of the anterior chamber and corneal endothelial cell count will also be
      done.

      Based on gonioscopy and anterior segment OCT findings, the primary mechanism of angle closure
      will be analyzed. Depending on the major mechanism, they will be assigned to either Pascal
      Laser Iridotomy and Pascal Laser Peripheral Iridoplasty. Patients identified as having pupil
      block will be assigned to Pascal Laser Iridotomy and those identified as having plateau iris
      configuration, plateau iris syndrome or angle crowding will be assigned to Pascal Laser
      Peripheral Iridoplasty.

      Post laser follow up will be done after 1 week, 1 month, 3 months and 6 months.

      PASCAL LASER IRIDOTOMY Prior to laser procedure 1 drop each of Alphagan-P and 4% Pilocarpine
      are instilled 15 minutes prior.

      A. Scanning Laser Parameters

        1. Set the pattern mode to square array, 2 x 2 spots, 0.25 distance between spots.

        2. Set pulse duration to 20 ms

        3. Adjust spot size to 100 um.

        4. Apply spots to peripheral iris preferably in the area between 11:00 and 1:00 o'clock
           position, positioning within an iris crypt until there is thinning of the iris stroma
           with a honeycomb apearance is obtained. The desired result is the appearance of a small
           hole with a dark brown base at the base of the burn and dispersion of debris into
           anterior chamber.

      B. Penetrating Burn with Yag Laser

        1. Set power to 2-3 mJ

        2. Apply laser burns to center of the hole until a mushroom cloud admixed with aqueous
           balloons into the anterior chamber.

        3. Enlarge the hole until approximately 300 um or more.

      C. Lens: Abraham lens

      PASCAL LASER PERIPHERAL IRIDOPLASTY Prior to laser procedure 1 drop each of Alphagan-P and 4%
      Pilocarpine are instilled 15 minutes prior.

      A. Titrate Average Laser Power

        1. Set the pattern mode to single spot

        2. Set the pulse duration to 100 ms

        3. Adjust spot size to 100 um

        4. Apply spots at the peripheral iris one at a time while increasing average power until
           adequate contraction of peripheral iris is seen.

      B. Scanning Laser Parameters

        1. Choose the number of rows of spots (2-4) depending on dose.

        2. Choose spot separation between arcs from -0.25 to 0.25 spot diameter. One spot diameter
           = 100 um.

        3. Choose spot spacing within each arc from 0 to 1 spot diameter depending on dose.

        4. Set radius of the arc to match the curvature of the peripheral iris.

      C. Contact lens: CGIL lens

      Treat 360 degrees of peripheral iris with a total of 20-24 burns.

      DEFINITION OF OUTCOMES The main outcome measures are the difference in the pre laser and post
      laser intraocular pressures and the opening of angles documented by gonioscopy and anterior
      segment OCT.

      Secondary outcome measures are the pain and inflammation associated with the procedure as
      seen through slit lamp examination grading of anterior chamber cells and flares and laser
      flare meter analysis, and the possible changes in the corneal endothelium as seen in the
      specular microscopy.

      Details of Examination Procedures:

        1. Visual Acuity Visual acuity: This will be assessed using a logMAR chart under standard
           lighting: best corrected visual acuity will be recorded (using the subjective refractive
           correction obtained above). Subjects will start reading at the 6/12 equivalent line
           (0.3) and if unable to read at least three letters, they will begin to read the line
           above and continue this process until at least three letters on one line have been read.
           This line will be recorded as the visual acuity. If the subject is able to read at least
           three letters on the first line, they will proceed on to the next line below, until they
           are unable to read further down the chart. If unable to read the chart at 4 m, the
           subject will be moved to 2m, and then 1m from the chart. If unable to see/achieve
           minimum recordable logMAR acuity, the vision will be recorded as perception or
           non-perception of light.

        2. Goldman Applanation Tonometry The IOP will be measured by Goldman Applanation Tonometry
           after instillation of a topical anesthetic. The IOP at every visit will be taken using
           the same slit lamp and tonometer. Three consecutive readings will be taken and the mean
           of the three values used in the statistical analyses.

        3. Slit lamp Biomicroscopic Examination Slit lamp biomicroscopic examination will be
           performed on the same slit lamp every visit. Examination of the conjunctiva, cornea,
           anterior chamber and lens will be done and any abnormalities noted. The lens will be
           graded using the Lens Opacity Classification Scale III (LOCS III). The anterior cells
           and flares will be graded as follows: A parallelepiped about 2 mm wide and 4 mm high at
           45 degrees will be directed into the pupil. The following table will be used9.

           Grade Aqueous Cells Grade Flare 0 None 0 Complete absence 1 5-10 cells per field 1 Faint
           flare (barely detectable) 2 10-20 per field 2 Moderate flare (iris and lens details
           clear) 3 20-50 cells per field 3 Marked flare (iris and lens details hazy) 4 50 + cells
           per field 4 Intense flare (fixed, coagulated aqueous humor with considerable fibrin)

        4. Gonioscopy Gonioscopy will be performed on all patients using Sussman 4-mirror
           gonioscopy lens to facilitate indentation gonioscopy. Findings in each quadrant will be
           graded using the Shaffer System and recorded in a goniogram.

        5. LOCS III Lens Opacity Grading System LOCS III lens opacity grading system will be used
           to assess if there will be developing cataract or increasing degree of cataract
           associated with the laser procedure. It will be done on the baseline visit as well on
           all follow-up visits.

        6. Visual Field Testing Humphrey Visual field Analyzer will be used with the program of
           SITA standard, 24-2 test. For the visual fields to be reliable, the following criteria
           should be followed: fixation losses of less than 33%, false positive errors of less than
           20% and false negative errors of less than 20%. Mean deviation and pattern standard
           deviation will be compared on each test to determine progression of the disease.

        7. Anterior Segment OCT Anterior segment OCT using Carl Zeiss Visante is an non-contact
           imaging system used to assess the anterior chamber anatomy especially the anterior
           chamber angles. It will be performed prelaser, 1 week, 1 month, 3 months and 6 months
           post laser.

        8. Flare Meter The Kowa FM-600 Laser flare meter will be used to assess anterior chamber
           inflammation. Five measurements will be taken and the average will be recorded as the
           correct value. Results will be expressed in photons/ms.

        9. Corneal Specular Microscopy Non-contact specular microscopy will be performed at the
           central and peripheral regions of the cornea using Topcon SP-2000P.

      This method measures the state of the corneal endothelium, the parameters to be determined
      are endothelial cell density, cell area, coefficient of variation (CV) in cell area and
      hexagonality.

      SCHEDULE OF STUDY VISITS Recruitment visit Baseline assessment will be done upon referral for
      inclusion in the study.

      Treatment Visit Pascal Laser Iridotomy or Pascal Laser Peripheral Iridoplasty will be done.

      Follow-up Visits Follow-up examinations will be performed 1 week, 1 month, 3 months and 6
      months after the laser procedure. The following examinations will be done on each postlaser
      visit: visual acuity, slit lamp examination, intraocular pressure determination, lens opacity
      evaluation, gonioscopy, anterior segment OCT, laser flare meter examination of anterior
      chamber inflammation, Humphrey visual fields(baseline & six months) and corneal endothelial
      cell count.
    

Intervention name(s): pattern scanning laser iridotomy and iridoplasty
Intervention type(s): Procedure
Intervention description(s): peripheral laser iridotomy and iridoplasty using pattern scanning laser technique
Other intervention name(s): PASCAL
Allocation: Non-Randomized
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: iridotomy; iridoplasty; angle closure glaucoma