CURRENT CONCEPT IN DIAGNOSIS & MANAGEMENT OF GLAUCOMA
CURRENT CONCEPT IN DIAGNOSIS & MANAGEMENT OF GLAUCOMA
( Published by Cipla India to be distributed to Indian Ophthalmologists)
Dr. M. R. Jain, a leading glaucoma specialist, is presently Medical Director and Chief Ophthalmologist M. R. J Institute and Jain Eye Hospital Jaipur, India. He has edited Text book on Glaucoma and a Book on OCULAR INFLAMMATION and published 130 scientific papers in India and abroad. In year 2007, he published public education book in Hindi on, “ EYES: SAFETY & TREATMENT”
He has been awarded LIFE TIME ACHIEVEMENT AWARD by Rajasthan Ophthalmological Society in the year 2002 & LIFE TIME ACHIEVEMENT AWARD by All India Ophthalmological Society, 2006
Dr. Jain is awarded Gold Medal by the ‘National Academy of Medical Sciences’ for research and clinical work in the field of “Glaucoma and Drug Delivery to the eye.”
Presently Dr Jain is Chairman, Dr M. R. J Charitable Trust, Chairman, Lucky Seventh, SMS Medicos and State Convener for National Academy of Medical Sciences.
CURRENT CONCEPTS IN DIAGNOSIS AND
MANAGEMENT OF GLAUCOMA
PROF. M. R.JAIN, M.S., F.I.C.S.(USA), FAMS, FACLP( London) MEDICAL DIRECTOR M.R.J.INSTITUTE
& JAIN EYE HOSPITAL JAIPUR
E MAIL : drmrjain55@gmail.com
There has been a revolutionary change in understanding, diagnosis and management of glaucoma. Earlier the glaucoma was defined as a condition of raised intraocular pressure, not compatible with health and function of eye. Presently, American Academy Of Ophthalmology has defined glaucoma as an optic neuropathy with characteristic structural damage to optic nerve, associated with progressive retinal ganglion cell death, loss of nerve fibers and visual field loss. The importance of intraocular pressure above 21.0 mm of Hg as a singular factor has been significantly minimized since about one-third of patients might show classical glaucomatous damage with normal intraocular pressure (1,2) or in spite of controlled IOP after glaucoma surgery, there may be progressive loss of fields.
The definition of glaucoma is based on visually significant end-organ damage (3) . It is conclusively opined that IOP related damage can occur at all levels of IOP, and hence almost 50 percent of glaucoma patients remain undiagnosed (4-6) . However, Baltimore Eye Survey and Aravind Comprehensive Eye Study reveal that the relationship between the intraocular pressure and the prevalence of glaucoma is positive. Generally, 21mm of Hg is considered as a cutoff point.
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MODERN DIAGNOSTIC MODALITIES
OPTIC NERVE HEAD IMMAGING
In addition to the well established Direct Ophthalmoscopy and Slit Lamp Indirect Ophthalmoscopy using 90 diopters of lens, newer diagnostic tools are available to precisely visualize and document subtle changes in the disc, depending upon the contour, colour, cupping and the health of neuroretinal rim. (7-10) These are as follows:
1. PHOTOGRAPHY TECHNIQUE
(a) STEREO PHOTOGRAPHS
2. COMPUTERISED IMAGE ANALYSIS
(a) OPTICAL COHERENCE TOMOGRAPHY (OCT)
(b) CONFOCAL SCANNING LASER TOMOGRAPHY (CSLT)
(c) SCANNING LASER POLARIMETRY (SLP).
These modalities are especially useful to quantitatively assess retinal nerve fibre layer (RNFL) thickness in addition to changes in the disc in suspected cases of glaucoma. It is established that retinal nerve fibre layer in glaucoma may show thinning even before the field changes are detected (11-14).
Optical Coherence Tomography (OCT) scan of a normal 2 glaucomatous eye, showing nerve fibre thickness.
Heidelberg Retinal Tomograph (HRT and HRT II) is a confocal laser scanning system for acquisition and analysis of three-dimensional images of optic nerve head. HRT imaging system has the highest diagnostic precision, accuracy, reproducibility and is able to diagnose glaucoma before confirmed visual field change. (15,16)
Kamal et al (17) and Greaney et al (18) observed that imaging techniques were not better than quantitative assessment of disc photographs. In addition to progressive excavation of the optic disc, the health of neuroretinal rim evidenced by its width and colour is very important (8) . Localized unilateral notch in the inferio-temporal or superio-temporal part of neuroretinal rim is strong indicator of glaucoma. Several other soft signs like asymmetry of cup/disc ratio greater than 0.2, peripapillary halo, disc hemorrhage, Herschler’s sign of exposed floor vessels, vertical ovality of optic cup with a ratio of greater than 3 and few others when present, adds to suspicion of glaucoma. In recent years, more importance is given to a disc hemorrhage crossing the rim of the optic nerve and it is considered to be associated with the acquired pit of the optic nerve (APON), which is a very strong association of glaucoma (16,19) .
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ADVANCEMENT IN AUTOMATED FIELD RECORDING
Introduction of computerized automated field testing has helped us significantly to diagnose glaucoma at an early stage as well as it provides certain amount of documentation to monitor the control and progression of glaucoma.
Last decade has seen immense advances in test strategies, which has made the process quick, precise, reliable and reproducible. (20,21)
SITA (Swedish Interactive Threshold Algorithm) and TOP (Tendency Oriented Perimetry) test strategies have reduced the testing time and provided variability of automated perimetric testing.
Frequency Doubling Technology (FDT) perimetry is very rapid and effective method to detect glaucomatous field loss.
Short Wavelength Automated Perimetry (SWAP) is able to predict the onset and progression of glaucomatous visual field deficits much earlier than the Standard Automated Perimetry (SAP)
Multifocal Electroretinogram (mfERG) and Multifocal Visual Evoked Potential (mfVEP) provide an objective measurement of the visual field.
Recent studies suggest that mfVEP procedures may be able to detect glaucomatous damage earlier than the conventional automated perimetry. Goldberg and associates (22) noted that 60 percent of fellow eyes of glaucoma patients that had normal Humphrey visual field were identified as abnormal by the mfVEP.
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INTRAOCULAR PRESSURE
Last decade has not seen any significant advancement in the methodology of recording IOP. In spite of several types of tonometers including Applanation Pneumatonograph, Mackay Marg Electronic Tonometer, (23-27) , Tonopen XL (blood flow tonometer) (28) and even Non Contact Tonometer, Goldman Tonometer remains the most reliable clinical Tonometer, wherever it is possible to employ this technique. Non Contact Tonometer is convenient to the patient and to the doctor but the readings quite often does not compare well with the Goldman Tonometer. The machine needs repeated standardization and has several limitations. Apart from scleral rigidity, abnormal central thickness of the cornea can affect the intraocular pressure reading (29, 30) .
What has changed in the last decade is the understanding of ideal IOP. Such an IOP has been labelled as TARGET IOP.
Target IOP is defined as that IOP which is safe for that particular person. It may be anywhere between low-teens to 21 mmHg.
Target IOP is set on following principles :
a. Mild Field Loss: Reduce IOP 20% less of initial IOP
b. Moderate Damage: 30% reduction or more.
c. Severe Damage: 40% reduction or more.
There is no IOP at which an individual is completely safe from glaucoma damage and hence target IOP has to be individualized depending upon repeated examination of disc and the fields. Risk factors such as aging, myopia, heredity, diabetes etc (31) too have to be kept in mind.
The outcome of the Advanced Glaucoma Intervention Study (AGIS) data suggest that lower the IOP the better, regardless of other risk factors that are accounted for clinically. In younger patients, the IOP should be maintained relatively low (32) .
Most therapeutic decisions in glaucoma are based on the steady state pressure. Ophthalmologists rarely document transient or episodic spikes in pressure or consider the damage that such spikes can cause. But such episodic spikes are significantly damaging to the RGS (33) . Postural change in IOP where the IOP is reported to increase in supine posture as compared to sitting posture, which is usually employed in Goldmann or Non- Contact Tonometry, may miss some of the glaucoma cases (23-27).
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PERFUSION PRESSURE
Glaucomatous field damage is associated with decrease in perfusion pressure of lamina cribrosa and neuroretinal rim. It is opined that vascular deregulation interferes with the auto regulation of ocular perfusion and renders the eye more sensitive to IOP increase or blood pressure decrease. This partly explains the theory of field loss at low intraocular pressure and highlights the significance of using only those anti-glaucoma drugs, which do not compromise the perfusion pressure of the optic disc (34,35).
Perfusion pressure
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