COMPARATIVE EVALUATION OF TRABECULECTOMY IN PRIMARY OPEN ANGLE GLAUCOMA AND PRIMARY ANGLE CLOSURE GLAUCOMA

Glaucoma is the leading cause of irreversible blindness in the world with an estimated 34 millionpeople worldwide being affected by 2040.Glaucoma can be classified into primary and secondary which decide treatment protocol. Primary angle closure glaucoma (PACG) is a major form of glaucoma in east Asia while primary open angle glaucoma (POAG)  predominates in  Caucasians and Africans. Recent glaucoma prevalence studies in south India found that prevalence of PACG is high at 4.32%. It is estimated that PACG blinds more people than POAG in absolute terms although the number of POAG worldwide is higher. By 2020 PACG would affect 20 million people and an estimate of 5.3 million could be blind.

Trabeculectomy creates a new path for aqueous outflow which bypasses the diseased trabecular meshwork and forms a bleb. Bleb functionality and longevity is determined by extent of subconjunctival fibrosis, the latter being the commonest cause of bleb failure. Conjunctiva being the reservoir of fibroblast recruitment at the time of filtration surgery, its preoperative health is likely to play a crucial role in tissue behavior in response to trauma of surgery.

Primary angle closure glaucoma PACG eyes have been documented to present with higher Intraocular pressure (IOP). Recurrent bouts of high IOP in these eyes result in ischemia, reperfusion injury, manifesting with iris atrophy and subclinical inflammation in conjunctiva of ACG eyes. Anatomical aspects of ACG with smaller eyeballs, smaller palpebral fissure and shallow fornices, thicker iris and thicker lens make trabeculectomy challenging. Concomitant tear film dysfunction subsequent to long term use of anti-glaucoma medications (AGM) resulting in deranged conjunctival milieu reduces chance of bleb survival. Due to the above reasons, filtering surgery in PACG behaves differently from POAG eyes.

Keeping the immensity of PACG in India, it’s tendency to cause more blindness, its surgical differences in mind, we propose to study trabeculectomy outcomes in angle closure glaucoma v/s open angle glaucoma with respect to bleb morphology and function. Conjunctival cellular profile would be studied for cell markers of inflammation and linkage if any, to bleb survival.

LACUNAE IN EXISTING KNOWLEDGE

1.     To the best of our knowledge there is paucity of data in Indian population comparing trabeculectomy outcomes in Primary Angle Closure Glaucoma and Primary Open Angle Glaucoma.

2.     Paucity of data on relationship of conjunctiva cellular profile with respect to bleb  functionality and morphology in Primary Angle Closure Glaucoma eyes.

AIMS AND OBJECTIVES

1)     To compare surgical outcome of trabeculectomy in Primary Angle Closure Glaucoma  and Primary Open Angle Glaucoma eyes.

2)     Correlate conjunctival cellular profile with bleb function and morphology.

MATERIAL AND METHODS

STUDY TYPE: Prospective comparative study

SETTING: Department of Ophthalmology, Guru Nanak Eye Centre, Maulana Azad Medical College & associated hospitals, New Delhi

STUDY DESIGN: Hospital based, prospective comparative study

SAMPLE SIZE: The study of Maheshwari, D et al in 2019 observed that mean intraocular pressure at 6 months in open angle glaucoma was 10.5 ± 2.6 and in angle closure glaucoma was 12 ± 3.8. Taking these values as reference, the minimum required sample size with 80%power of study and 5% level of significance is 74 patients in each study group. So total sample size taken is 150 (75 patients per group).

SAMPLE SIZE CALCULATION

Formula used is:

For comparing mean of two groups

N>=2(standard deviation)2 *(Zα + Zβ)2 (mean difference)2​

Where Zα is value of Z at two sided alpha error of 5% and Zβ is value of Z at power

of 80% and mean difference is difference in mean values of two groups.

Pooled standard deviation= Sqrt(((S1)2+(S2)2)/2)

Where S1 is standard deviation of 1 group.

And S2 is standard deviation of other group.

Calculations:

Pooled standard deviation=sqrt(((2.6)2+(3.8)2)/2)  =3.25

N>=2(3.25)2 *(1.96 + .84)2

(1.5)2​>=73.61=74(approx.)

But due to time constraints we will take a convenience sample size of 60 ,that is 30 POAG patients and 30 PACG patients.

INCLUSION CRITERIA

1.     Uncontrolled  primary glaucoma requiring trabeculectomy

2.     Age >18 years

3.     Patient willing to follow up for minimum 4 months.

EXCLUSION CRITERIA

1.     Prior incisional surgery involving conjunctiva

2.     Dry eyes

3.     Use of long term topical steroids

4.     Chronic ocular pathology like keratitis, uveitis, episleritis and scleritis.

  OUTCOMES EVALUATED

PRIMARY OUTCOME

1. Bleb functionality and morphology

2. Conjunctival cell profile

 SECONDARY OUTCOME

1. Conjunctival inflammation correlation with bleb function and morphology

 STUDY PROTOCOL

Suitable patients meeting the inclusion criteria will be enrolled in the study and evaluated on the above said parameters prior to the surgery. Patients will be divided into two groups.

Group 1- POAG undergoing trabeculectomy.

Group 2- PACG undergoing trabeculectomy.

Trabeculectomy with releasable sutures with use of mitomycin C 0.02% for 2 min restricted to patients younger than 50 years, would be performed by the same surgeon.Aconjunctival frill incision followed by a triangular superficial flap of 4 X 4mm followed by 2X1 mm sclerostomy by Kelly Descemet punch and large peripheral iridectomy would be done. The scleral flap would be closed by one fixed and 2 releasable sutures. Conjunctival closure by   8-0 nylon would be followed by on table titration of bleb.

The conjunctival tissue biopsy would be taken from inferior conjunctiva of size 2X3 mm at the time of trabeculectomy. The tissue would be immediately fixed in 10% buffered formalin and processed as per protocol  to have formalin fixed paraffin embedded (FFPE) tissue. Thin sections of 5 microns will be cut. Care would be taken to orient sections to obtain epithelium and stroma. Cut sections would be stained for hematoxylin and eosin, PAS with Diastase with Alcian blue. Immunohistochemistry would be performed as per protocol of various primary antibodies.

PRIMARY ANTIBODIES

a)     T Cells -CD3, CD5

b)     Macrophages-CD68

c)     Mast cell-CD117

d)     Fibroblast-Vimentin

Bleb functionality and morphology would be assessed by

a)Intraocular pressure control

b)  Slit lamp examination- IBAGS classification

c) Anterior segment Ocular coherence tomography (AS SOCT)

Patients would then be subsequently evaluated on post- operatively on Day 1, Day 7, 1 month, and 4 months.

 Parameters evaluated**:**

â—      Intraocular pressure(IOP): measured by Goldman applanation tonometry (GAT)

â—      Conjunctival  biopsy : Cellular profile : macrophages(CD68), lymphocytes(CD3,CD5) fibroblast(vimentin),goblet cell(PAS with diastase with alcian blue), mast cells(CD11

â—      Best corrected visual acuity (BCVA)

â—      Slit lamp examination:

i) AC reaction:Standard Uveitis Nomenclature (SUN Classification)

ii) Cataract state (LOCS)

iii) Bleb morphology assessment: IBAGS

·       Anterior segment optical coherence tomography (ASOCT)

Bleb characteristics evaluated would be-

-Bleb wall thickness at - i) 12 O’ clock position

ii) At area of greatest height

-Bleb reflectivity would be evaluated throughout bleb area.

â—      Ocular surface Disruption: by Tear Break Up Time (BUT) and keratometry

â—      Complications during or after surgery including the requirement for Bleb needling.

â—      Visual  fields examination  by Humphrey field analyzer 24-2/10-2 as required

â—      Number of anti-glaucoma medications used

 STATISTICAL EVALUATION

SAMPLE SIZE: The study of Maheshwari D , et al in 2019 observed that mean intraocular pressure at 6 months in open angle glaucoma was 10.5 ± 2.6 and in angle closure glaucoma was 12 ± 3.8. Taking these values as reference, the minimum required sample size with 80% power of study and 5% level of significance is 74 patients in each study group. So total sample size taken is 150 (75 patients per group).

   Formula used is:

For comparing mean of two groups

N>=2(standard deviation)2 *(Zα + Zβ)2

(mean difference)2​

Where Zα is value of Z at two sided alpha error of 5% and Zβ is value of Z at power

of 80% and mean difference is difference in mean values of two groups.

Pooled standard deviation= Sqrt(((S1)2+(S2)2)/2)

Where S1 is standard deviation of 1 group.

And S2 is standard deviation of other group.

 Calculations:

Pooled standard deviation=sqrt(((2.6)2+(3.8)2)/2) =3.25

N>=2(3.25)2 *(1.96 + .84)2 , (1.5)2​>=73.61=74(approx.)

STATISTICAL ANALYSIS

Categorical variables will be presented in number and percentage (%) and continuous variables will be presented as mean ± SD and median.  Normality of data will be tested by Kolmogorov-Smirnov test. If the normality is rejected then non parametric test will be used.

Statistical tests will be applied as follows-

1.Quantitative variables will be compared using Unpaired t-test/Mann-Whitney Test (when the data sets were not normally distributed) between the two groups.

2.Qualitative variables will be compared using Chi-Square test /Fisher’s exact test.

A p value of <0.05 will be considered statistically significant.

The data will be entered in MS EXCEL spreadsheet and analysis will be done using Statistical Package for Social Sciences (SPSS) version 25.0.

Type of Study:  Prospective comparative study

 ETHICAL CONSIDERATIONS

â—      Informed consent will be taken from each study subject

â—      Confidentiality will be maintained for each study subject

â—       Subjects will have freedom to opt out of study at any point of time

â—       Prior approval of ethical committee of Maulana Azad Medical College will be taken prior to conduct of study