Friday, August 11, 2017

The BOSs (….or the hostile takeover of the filtering bleb)

A few years back it was suggested that cystic blebs often failed due to development of scar (fibrous) tissue occurring posteriorly (Figure 1). 

Figure 1. The Ring of Steel in cystic blebs

This was called the “RING OF STEEL” (Figure 2).

Figure 2

However, what happens in flat blebs? These failing blebs do not show any significant bleb formation but start to develop a progressive increase in intraocular pressure (IOP), usually after a period of initial good IOP control.

Fibrous tissue overlying the bleb, causing failure

I did surgical revision of such failing blebs and found a band of tissue overlying the bleb area. This had effectively sealed the scleral flap, preventing aqueous from going out from under the flap. I have named this tissue, found in the subconjunctival area, as theBAND OF STEEL (BOS). This BOS is responsible for bleb failure in these cases.

As seen in the following figures, this tissue appears as a band and has to be completely excised in order to free the scleral flap. After excision of the BOS, I usually place Mitomycin-C 0.04% for about 3 minutes over the affected area. This is a higher concentration than the MMC 0.02% which I had been using previously. This higher concentration might be more conducive to prevent fibrosis and prevent formation of the “band of steel”.

BOS is being cut

The cut piece of BOS

Monday, August 7, 2017


On 6th of August, 2017  we started our journey to visit Pitas Hospital. 

Located 169 kilometers from Kota Kinabalu, the small town is situated on the far boundary of the state. Due to its location and other factors, it is often difficult to have patients coming down to our hospital for treatment. 

The trip took more than 3 hours by a fast 4-wheel drive for us. The same trip can stretch to more than a day and cost a couple of hundred dollars for the patients who are dependent on infrequent public transports. Thus, our visits to such hospitals are a big boost for the healthcare of these impoverished populations. 

Since, the place is so far off, we had started in the afternoon of the 6th of August. We reached the Orkid Lodge by evening (Orkid is the spelling of orchid in the Malaysian language). The small lodge had minimal comforts. A TV with a single channel greeted us. There was no mineral water or coffee making facility. So we rushed down to the restaurant situated near the lodge. I ordered "roti canai". The accompanying curry was very oily and put me off. I quickly went back to my room, where I watched a movie on my laptop. By 10pm I had fallen asleep.

The next day, 7th August 2017, the hospital hilux took us to the OPD clinic. We were expecting 4o patients. After a quick breakfast of noodles and coffee we started work. Ultimately about 30 patients turned up for the clinic. We diagnosed a few cataract and glaucoma patients among others. Just after 12 noon we started our journey back. On the way back we stopped to buy some roasted corns. These are the sweet corns which are roasted within the leaves giving a peculiar smell and taste to them. We encountered heavy rains on the way and reached our hospital by 4 o'clock in the afternoon.

Tuesday, August 1, 2017


August is the month of independence from colonial rule in India. For this month our guest author is one of the most influential ophthalmologists from India: DR DALJIT SINGH. Born on 11th October 1934, he obtained his MBBS from the Government Medical College, Amritsar in 1956. He served as a member of faculty of the Government Medical colleges in Amritsar and Patiala for 23 years and became an Emeritus professor of these institutions. The Government of India awarded him the fourth highest civilian award of Padma Shri in 1987. Seven years later, he received the Dr. B. C. Roy Award, the highest Indian medical award from the Medical Council of India. At 82 years of age he remains as passionate as ever in writing and clinical work. This article traces his long journey in glaucoma surgery. "The Glog" is honored to have him here as a guest author. Our deepest thanks to him for sharing his thoughts.


Saturday, July 22, 2017


The Ministry of Health organized a cataract phacoemulsification camp (KK1M) in the town of Keningau, Sabah, Malaysia from 21st July 2017 to 23rd July 2017. It was an honor to be a part of the team which operated there.

Around 35 patients were operated there by the team of ophthalmologists from Queen Elizabeth Hospital, Ampang Hospital and Keningau Hospital. 

Aurovue intra-ocular lenses were implanted in almost all patients.

Thursday, July 13, 2017

Xen implant demonstration

On 12th July 2017, had the opportunity to visit Dr Peter Kong Specialist Eye Center in Kota Kinabalu and witness the first Xen implantation in Sabah state of Malaysia. The first patient was a lady with primary angle closure glaucoma in whom a Xen implantation alone was done. The other, another female patient had an open angle glaucoma, in whom a phacoemulsification as well as Xen implantation was done.

Observing the technique from close, it seems like there is a learning curve to this procedure, though not a very steep one. Two things noticed were: (i) the insertor can be made more user friendly and (ii) the company should find an appropriate blade to put the insertor in the anterior chamber so that the insertor and anterior chamber depth remain stable during the procedure.

Sunday, July 9, 2017

Retinal Nerve Fiber Layer Thickness (RNFLT) assessment 

This is a primer regarding: "Retinal Nerve Fiber Layer Thickness (RNFLT)  assessment using the CIRRUS Optical coherence tomography (OCT) machine".

The Cirrus RNFL map represents a 6 x 6 mm cube of A-scan data centered over the optic nerve in which a 3.4 mm diameter circle of RNFL data is extracted to create what is referred to as the TSNIT map (temporal, superior, nasal, inferior, temporal).  It is displayed as a false color scale with the thickness values referenced to a normative database. The TSNIT map displays RNFL thickness values by quadrants and clock hours, and the RNFL peaks give a sense of the anatomic distribution of nerve fiber axons represented by the superior and inferior bundles that emanate from the optic nerve.

SD-OCT measurements are compared against an age-matched normative database. The normative database for the Cirrus SD-OCT consisted of 284 healthy individuals with an age range between 18 and 84 years (mean of 46.5 years). Ethnically, 43% were Caucasian, 24% were Asians, 18% were African American, 12% were Hispanic, 1% were Indian, and 6% were of mixed ethnicity. The refractive error ranged from -12.00 D to +8.00 D.  Due to this relatively small normative database and wide variation of distribution of RNFL, many results obtained by SD-OCT may be flagged as abnormal statistically in patients who are not represented in the database and thus not necessarily representing real disease. Clinicians should use caution to avoid overtreating “red disease” in these situations.

The Cirrus normative comparison for ONH parameters is based on the patient’s age and disc size; while, for the RNFL is based on patient’s age. For a particular age and disc size the patient is expected to have rim volume, C/D ratio etc within certain ranges. Those parameters are shaded red, yellow, green and white based on how they compare with normal ranges. When no normative data is available for comparison, the parameters are shaded grey. This applies to disc areas <1.3 mm2 or >2.5 mm2, since the database has insufficient number of subjects with the disc areas of these sizes.

Average RNFL thickness indicates a patient's overall RNFL health. The mean value for RNFL thickness in the general population is 92.9 +/- 9.4 microns. Typically, a normal, non-glaucomatous eye has an RNFL thickness of 80 microns or greater. An eye with an average RNFL thickness of 70 to 79 is suspicious for glaucoma. An average thickness of 60 to 69 is seen in less than 5% of the normal population and implies glaucoma.

Based on a longitudinal study, the age-related rate of reduction in RNFL thickness has been estimated to be -0.52 µm/year, -1.35 µm/year, and -1.25 µm/year for average, superior, and inferior RNFL respectively.

The best quality scans have signal strength greater than 8 (minimum acceptable scan > 6).


                                 i.OCT images can be acquired through a 3mm pupil in the absence of media opacities.

                                ii.However, a dilated pupil makes the procedure easier and reduces acquisition errors.

                           iii. The patient can be asked to blink a few times before image acquisition is started.

                                  iv. A lubricant eyedrop can be instilled in case of dry eyes.

                                 v.The patient is asked to look into an internal fixation target. (Green star-like in Cirrus)

                                  vi.A circular or rarely a linear image is then acquired. 

(B). OCT REPORT PRINT-OUT: The Cirrus report shows assessment of the RNFL and ONH of both eyes based on the 6mmx6mm cube captured by the Optic Disc Cube 200x200 scan. Some models of the OCT can display optic disc modules including parameters such as rim area, disc area, average- and vertical- C/D ratio.

1.       KEY DATA: This forms the first part of information for the printout and consists of the date and time of test; registration number, age, sex and date of birth of the patient; technician, and the “signal strength”, which should be above 8.

2.       RNFLT MAP: Topographic map of RNFL thickness in an hourglass shape of yellow and red colors is typical of normal eyes. The color scale in microns on the left of the image for reference is also provided. Warm colors (red, yellow) represent thicker areas, while cooler colors (blue, green) represent thinner areas.

3.       RNFLT DEVIATION MAP: It depicts the map of RNFL deviation from normal values overlaid on an en face fundus image. It also shows the machine-derived boundary of the cup and the disc and also the calculation circle placement for the RNFL. It depicts the deviation from the normative database in the form of color-coded superpixels, utilizing only yellow and red colors. Green color is not used since most of the superpixels would be green in a normal individual and would be present over most of the image, obscuring the underlying fundus image. Thus, any region which is not red or yellow indicates it is within normal limits. This map gives a gross clue regarding the cup-disc ratio and position of the vessels in the cup. The RNFL deviation map is useful to discuss the condition with the patient.


4.       QUADRANT AND CLOCK-HOUR RNFLT: A display of the average RNFLT along the whole calculation circle is present on the top. Quadrant and clock hour averages are given below and color coded in the same scales as rest of the report (based on their P value with respect to deviation from age-matched data in the normative database of the OCT machine). They specify the location of the pathology quadrant and clock hour wise. 

5.       RNFL NORMATIVE DATABASE: In the protocol, normative database is visualized using a white-green-yellow-red color code. Color coding indicates the particular position of the A-scan in the graph, the quadrant mean values and the clock-position in the circular graphs and right and left columns of the table of data.  The patient’s RNFL is marked by a black (continuous [right eye] or dashed line [left eye]). If the line dips into the red area, it indicates thinning of the RNFL.

In an age-matched normal population, the percentiles regard each specific measurement of RNFL in the following way:

(i) The thickest 5% of measurements fall in the white area (White indicates >95%).

(ii)90% of measurements fall in the green area (Green falls between 5% and <95%).

(iii)The thinnest 5% of measurements fall in or below the yellow area (Yellow between 1% and <5%, indicating “suspect” area).

(iv)The thinnest 1% of measurements fall in the red area. Measurements in red area are considered outside normal limits (Red area falls in <1%).

6.       SYMMETRY: It indicates the extent of symmetry of the RNFLT in the TSNIT quadrants between the 2 eyes.

7.       RNFL-TSNIT THICKNESS GRAPH: This shows the plot of RNFLT on the Y-axis (vertical) and the retinal quadrants on the X-axis (horizontal). Normally, this has a “double-hump” appearance due to the thicker RNFL in the superior and inferior quadrants. 

8.       EXTRACTED RNFL TOMOGRAMS: They display the reflectivity of the RNFL. They are not of much clinical significance as far as decision making is considered.