Introduction
Glaucoma is a group of disorders characterized by chronic progressive optic neuropathy resulting in irreversible visual loss. Glaucoma is the second-leading cause of blindness in the world, accounting for up to 8% of total blindness.[1,2] It is estimated that there are more than 60 million cases of glaucoma worldwide, with an estimated prevalence of 2.65% in people >40 years of age.[2,3] The World Health Organization estimates that 4.5 million people worldwide are blind due to glaucoma.[3]
In India, the estimated number of cases of glaucoma is 12 million, around one-fifth of the global burden, with nearly 1.2 million people blind from the disease.[1] The National Blindness survey showed that glaucoma is the third major cause of blindness in India after cataract and refractive errors and responsible for 5.8% of blindness (VA <6/60).[4] It is perceived that glaucoma blindness is underestimated in these surveys as the blindness is defined on visual acuity criteria only without considering visual fields, which are defining criteria for glaucoma.
As visual loss from glaucoma is irreversible, early diagnosis is important for the timely initiation of treatment and preservation of vision. Patients with glaucoma may remain asymptomatic until the advanced stages of the disease; therefore, diagnosis of glaucoma often relies on the detection of abnormality on routine eye examinations.
The aim of this study is to determine the magnitude of glaucomatous damage in the asymptomatic subjects identified with primary glaucoma for the first time and thus to evaluate the significance and efficacy of screening measures for glaucoma.
Materials and Methods
We conducted an observational retrospective cohort study including 100 asymptomatic patients of 40 years and above, newly diagnosed with and started on the treatment for primary glaucoma. Patients with secondary causes of glaucoma, such as steroid induced, traumatic, inflammatory, and neovascular and patients with poor visual acuity due to nonglaucoma reasons, were excluded from the study.
A thorough evaluation of all the recorded data of the first intraocular pressure (IOP) was performed using Goldmann applanation tonometry, central corneal thickness (CCT), vertical cup-to-disc (VCD) ratio, gonioscopy, retinal nerve fiber layer (RNFL) analysis on optical coherence tomography (OCT) and the first reliable standard automated perimetry (SAP) 30-2 SITA-std program of the Humphrey Field Analyzer within first 6 months of diagnosis.
The first suspicious indication for glaucoma work-up in all the cases was noted.
Patients were categorized into having early, moderate, and severe glaucoma, according to SAP mean deviation (MD) in the worse eye, with MD of <−6, −6 to −12 and >−12 dB, respectively.[5]
Factors such as age, gender, history of diabetes mellitus (DM), awareness about routine glaucoma check-ups, family history of glaucoma, IOP, CCT, and the angle width were correlated with the severity of glaucoma at presentation and statistically analyzed. A value of P < 0.05 was considered statistically significant.
Ethical clearance was obtained for the study from the institute review board in writing.
Results
The study was conducted on 100 patients diagnosed with primary glaucoma. The average age of the study population was 62.95 ± 10.63 years, 50 (50%) patients were males and 50 (50%) were females. 32 (32%) patients had a positive history of DM and 10 (10%) patients had a positive family history of glaucoma. 28 (28%) patients had taken an appointment for routine glaucoma screening. 21 (21%) patients in our study had suspicious Van Herick grading (VHG). 35 (35%) patients were found to have narrow angles in one of the eyes on gonioscopy.
32 (32%), 33 (33%), and 35 (35%) patients were found to have early, moderate, and severe stages of glaucoma with average MD of −3.51 ± 1.53, −8.65 ± 1.64, −17.15 ± 5.13 and mean VFI of 96.32% ± 2.50, 87.03% ± 5.74, 68.07% ±18.75, on SAP, respectively [Figure 1].
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Figure 1: Distribution of patients as per glaucoma defects
The association of risk factors, such as age (P = 0.006) and glaucoma awareness (P = 0.044) with the severity of glaucoma, were statistically significant [Table 1]. There was no direct statistical correlation found between gender (P = 0.97), history of DM (P = 0.38), family history of glaucoma (P = 0.54), IOP (P = 0.78), CCT (P = 0.6), the angle width (P = 0.25), and the severity of glaucoma in our study.
Table 1: Co-relation of risk factors with severity of glaucoma
About 69% of patients were of age 60 years or more, of which 77% had moderate-to-severe disease [Figures 2 and 3].
Figure 2: Comparison of mean age and severity of glaucoma
Figure 3: Comparison of age and severity of glaucoma
72% of the patients had taken the appointment for nonglaucoma reasons. 74% of this population had moderate-to-severe disease compared to 50% of the patients who had glaucoma appointments [Figure 4].
Figure 4: Patients for glaucoma consultation
83% of the patients with severe glaucoma were unaware of the disease [Figure 5].
Figure 5: Comparison of glaucoma awareness and severity of glaucoma
50% of the patients with a family history had severe glaucoma in our study compared to 33% with negative family history [Figure 6].
Figure 6: Comparison of family history and severity of glaucoma
The basic indication which leads to detailed glaucoma work up was evaluated. All 100 patients were asymptomatic with good average vision. Twenty-eight patients had taken the appointment for routine eye check-up for glaucoma. One patient from the remaining 72 had a positive family history of glaucoma. Thirty-four patients from the filtered population had borderline or high corrected IOP. On routine ophthalmic check-ups, 5 of the remaining patients with suspicious angle width on VHG and 32 patients with suspicious ONH and VCD on dilated fundoscopy were worked up in detail for glaucoma evaluation [Figure 7].
Figure 7: Indication of glaucoma evolution
Discussion
Glaucoma was probably recognized as a disease entity in the 17th century, where the term was derived from the Greek term glaucoma meaning cataract or opacity of the lens implying the lack of understanding of this disease process. Today we understand that glaucoma is a group of diseases with common endpoint characteristics affecting the optic nerve and causing visual field losses. Major risk factors for developing glaucoma include higher IOP, greater cup-to-disc ratio, asymmetry of ONH cup, decreased CCT, older age, genetic factors, ethnicity, history of DM, pseudoexfoliation syndrome, and ocular perfusion pressure.[6]
Our study on 100 newly diagnosed glaucoma cases, around 2/3rd of the patients had presented with moderate-to-severe damage already happened (68%) These numbers are higher as compared to parallel studies, one of which had around 50% of patients with MD >−6.0.[7]
The probable reasons why patients with glaucoma remain undiagnosed can be the asymptomatic nature of the disease till advanced visual field loss happens, unawareness about the disease, socioeconomic factors,[8,9] multifaceted nature of the disease, lack of diagnosing facilities or it being not a part of routine ophthalmic check-ups.[10] Our hospital attends to patients under health scheme where consultations and management are covered and are easily available for the beneficiaries. All the patients above 40 years attending the outpatient department are screened for glaucoma. Despite the facilities available, the late stage of diagnosis indicates a demand for more public awareness programs.
As per Aravind’s comprehensive eye survey, it was observed that more than 90% of cases of glaucoma were undiagnosed and identified only at the time of the survey.[11] In our study population, only 28 out of 100 patients had taken appointment for glaucoma evaluation, half of which (50%) were found to have moderate-to-severe disease. Around 83% of patients having severe glaucoma (n = 29/35) were not aware of the disease. Spreading awareness of the disease can get more patients for the check-up and detecting glaucoma at the earlier stages.
All patients with a family history carry a higher risk for developing glaucoma and should be screened for the same.[12]
As per a study, people with a family history of glaucoma were estimated to be almost one-third as likely to have advanced field loss as those with no family history, the reason for the same being the knowledge about the disease and early screening for glaucoma.[13] In our study, the number of patients with a family history was directly proportional to the severity of the disease, though not statistically significant (P = 0.54). Screening for glaucoma was not the primary reason to visit the hospital for 1 of the 10 patients with positive family history of glaucoma, and he was found to have severe disease. 4 (44%) of rest 9 patients had severe glaucomatous changes. Health care does not halt at diagnosing and treating the disease, detailed counseling about the disease and the importance of screening of family members becomes a major part of the management.
In our study, around 69% of patients were of or above the age of 60. Visual disturbances secondary to cataract formation and postretirement free time can be common reasons to visit an eye OPD at this age. We found a significant statistical association between age and the severity of glaucoma (P = 0.006). The advanced disease in older patients can be due to accumulated damage. All patients above the age of 40 should be screened for the disease irrespective of the reason for the consultation for early detection and timely management.
Females are at higher risk of developing glaucoma.[6] There was no direct statistical correlation found between gender (P = 0.97) and the severity of glaucoma in our study.
Individuals with DM have a higher risk of developing glaucoma (primary open angle glaucoma [POAG]).[14] We had 32 (32%) diabetic patients in our study. We did not find any direct statistical correlation between history of DM (P = 0.38) and the severity of glaucoma in our study.
Diagnosis of glaucoma is not the result of a single test but requires a complete set of work up.[14]
In the past, raised IOP was used as a defining characteristic for glaucoma; but now, IOP is considered as just an important risk factor for glaucoma.[15,16] IOP measurement can be corrected as per CCT to avoid a false-negative result. 19 (19%) patients in our study had CCT <500 in one of the eyes. We found relatively thinner corneas in moderate and severe cases (528.49 ± 31.18) compared to mild cases (mean CCT 542.01 ± 35.18). Although the role of high IOP and thinner CCT as risk factors in the development of glaucoma are well established,[17] we did not find any significant statistical correlation between IOP (P = 0.78) and CCT (P = 0.6) with the severity of glaucoma. 46 (46%) of our patients had corrected IOP <21 mm of Hg on first evaluation. This concludes that IOP should not be the only measure to diagnose or rule out glaucoma.
Compared with the rates of blindness in POAG, population-based studies show that primary angle closure glaucoma, on average, carries a three-fold increased risk of severe, bilateral visual impairment.[18] VHG gives a fair suspicion about angle occludabilty and should be looked for before pupillary dilatation. 21 (21%) patients in our study had suspicious VHG, all of which had narrow angles on gonioscopy. More than 1/3rd (35%) of the patients had narrow angles in one of the eyes, more than 3/4th of which had moderate-to-severe glaucoma.
Typical optic nerve head changes in glaucoma include diffuse or focal narrowing (notching/shelving) of the neuroretinal rim (NRR) specifically at the superior or inferior part of the optic disc, increased VCD ratio, asymmetry of CDR of 0.2 or more, hemorrhage at or around the optic disc, bayonetting of vessels, deep (excavated) cup with bean-pot cupping and laminar dot sign, nasalization of optic disc vessels, and diffuse or focal (arcuate) thinning/defect of the RNFL contiguous with an area of NRR-notch.[6]
32 (32%) of our patients who had nonglaucoma reasons for consultation, a negative family history of glaucoma, IOP <21 mm of Hg, and nonsuspicious VHG, were found to have confirmed glaucoma with suspicious ONH changes. Therefore, all the patients attending eye OPD should be examined for dilated fundoscopy after ruling out occludable angles. Imaging technologies such as streophotography and OCT can be useful in screening cases.
SAP is a useful test to determine the extent of functional glaucomatous damage. In our study, average MD of −3.51 ± 1.53, −8.65 ± 1.64, −17.15 ± 5.13, and mean VFI of 96.32% ± 2.50, 87.03% ± 5.74, 68.07% ± 18.75 were found in early, moderate and severe cases, respectively.[5,19] The field loss due to glaucoma is irreversible, and hence, the aim of early diagnosis of glaucoma should be to pick up preperimetric glaucoma.
Reduction of IOP has been repeatedly demonstrated to be an effective intervention across the spectrum of glaucoma, regardless of subtype or disease stage.[15,20]
Appropriate medical, surgical, and LASER modalities help to achieve the target IOP and thus limit the visual loss due to the disease.
Early and accurate detection is crucial to treat the affected subjects, thus reducing the disability and the social burden of the disease.
Conclusion
Although glaucoma is the leading cause of irreversible blindness globally, the condition shows no signs or symptoms until later stages. Hence, early screening by detail glaucoma works up, and proper treatment is the only key to halt its progression. Despite available facilities, 68% of patients in our study were found to have moderate-to-severe stages of glaucoma. We also found a statistically significant association of older age (P = 0.006) and the glaucoma awareness (P = 0.044) with the severity of glaucoma. This indicates that our screening measures should reach the mass at the primary level too, with a focus on awareness programs.
Limitations
The study was conducted in a cohort of patients who were availing health care benefits from the services provided by the organization. The sociodemographic characteristics of this sample may not reflect that of the general population.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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