Dr.Tapas Ranjan Padhi

Dr. SUBHADRA JALALI, Dr.SRIKANTA KUMAR PADHY

Semi Finals

Abstract

In a prospective study, the rate of vascular outgrowth in babies with Retinopathy of Prematurity (ROP) of various degrees were analyzed and compared with normative controls. Measurements were done from the disc margin up to the end of blood vessels in fixed quadrants in disc diameter. The rate was calculated by dividing this value with the number of weeks elapsed during this vascular growth from disc margin up to their endings at the time of measurement. A total of 409 eyes, divided into treatable (Group 1),Spontaneously regressed (Group 2) and No ROP (Group 3) were analyzed. The overall average rate of vascular outgrowth was 0.466,0.605 and 0.732,0 DD/week respectively for Group III,II and I respectively. While eyes with a rate 0.46 DD/week or less invariably required intervention, none with a speed more than 0.702 DD/week required treatment. Rate of vascular outgrowth was observed to be an important ocular predictor of babies with ROP of various degree in the present series.

Full Text

Title page

Title- Can the rate of vascular outgrowth be a predictor of treatment in babies with retinopathy of prematurity?

*,#Tapas Ranjan Padhi,MS1; *Utpal Bhusal, BSc(Optometry)1; Srikanta Kumar Padhy,MD1;Anamika Patel,MS1;Anup Kelgaonker,MS1; Ashish Khalsa,DNB1; Taraprasad Das,FRCS2;Vidushi Kapil,MS1;Shalini Sugumar1;BalakrushnaSamantray, MS,3;Savita Devi, MS,4; Mohammad Hasnat Ali, PG (Advanced Biostatistics),Subhadra Jalali,MS2

1Retina and Vitreous services, LV Prasad Eye Institute, MithuTulsiChanrai Campus, Bhubaneswar, Odisha, India

1Pediatric retina services, Newborn Eye Health Alliance (NEHA), MithuTulsiChanrai Campus, Bhubaneswar, Odisha, India

1Pediatric retina services, Miriam Hyman Children Eye Care Center, MithuTulsiChanrai Campus, Bhubaneswar, Odisha, India

2Srimati Kanuri Santhamma Centre for Vitreoretinal Diseases, LV Prasad Eye Institute, Kallam Anji Reddy Campus Hyderabad, India

3Department of Biostatistics, LV Prasad Eye Institute, Kallam Anji Reddy Campus, Hyderabad, India

4Asst.Professor, Department of Ophthalmology, SCB Medical College, Cuttack, Odisha, India

5Asst.Professor, Department of Ophthalmology, MKCG Medical College, Berhampur, Odisha, India

*Tapas Ranjan Padhi and *Utpal Bhushal have contributed equally and deserve to be the co-first authors

Corresponding author (*,#) details

Tapas Ranjan Padhi

Faculty, Vitreoretinal services, Mithu Tulsi Chanrai (MTC) campus, LV Prasad Eye Institute, Patia, Bhubaneswar, Odisha, India, Pin751024

Fax: +91 674 3987130, Phone No.:+91 9438361078(M);+91674 3987999 (O)

Word count: Abstract-248, Text (excluding abstract, references, tables, and legends)-3054

Funding/Support: Hyderabad Eye Research Foundation

The authors acknowledge that the institute has received support from Queen Elizabeth Diamond Jubilee Trust (UK), Miriam Hyman Memorial Trust (UK), Rashtriya Bal Swasthya Karyakram (RBSK), and Dalmia Holdings (India) for its ongoing work in ROP.

Acknowledgment

The authors acknowledge Mrs. Bhavna Garg for her help in analyzing the data in the manuscript. 

Abstract

Purpose: To analyze the retinal vascular growth rate in treatment naïve babies with various stages of Retinopathy of Prematurity (ROP) and validate if this could be a predictor of treatment need.

Method: Retrospective review of medical charts and retinal images of babies with various stages of ROP. Using the length of the horizontal disc diameter (DD) of each eye, the vessel growth was measured from the disc margin up to the vessel tip in fixed quadrants. The rate of vessel growth was the ratio of vessel length to the number of weeks it took to reach this length. The babies studied were divided into treatment warranting ROP (Group 1), spontaneously regressed (Group 2), and no- ROP (Group 3) for analysis. The ‘no- ROP’ group acted as normal control. Group 1 was further subdivided into 1A (threshold ROP), IB (Aggressive Posterior ROP),1C (hybrid ROP), and ID (high-risk pre threshold ROP).

Result: Out of 436 eyes, Group 1, 2, and 3 had 238,108 and 90 eyes, respectively. The mean rate of vascular outgrowth along with 95% Confidence interval was 0.719 [0.703, 0.740], 0.612[0.599, 0.638], and 0.490 [0.487, 0.520] DD/week, respectively, for babies with No-ROP, spontaneously regressed ROP, and treatment warranting ROP. More than 80% of eyes with a vessel growth rate of 0.54 to 0.57 DD/week or less required treatment.

Conclusion: A retinal vascular growth of 0.54 DD/week or less could predict treatment requirements in babies with ROP.

Translational relevance: Rate of vascular growth could predict treatment requirement in ROP. 

Text

Introduction

Retinopathy of Prematurity (ROP) is a disorder of immature retinal vasculature. Up to 12 weeks of fetal life, the developing retina is supplied principally by the blood vessels from the developing hyaloid system and a contribution from the choroidal vasculature. Major retinal arteries begin from the center of the optic disc at 16 weeks of gestation and grow peripherally at a rate of 0.1mm per day.1It is also known that the internal vascular plexus of the retina grows 0.094–0.1 mm/day2 from 28 weeks of gestational age; this is equivalent to a vascularization rate of 0.7 mm/week or approximately 0.7 DD/week,3 taking mean horizontal optic diameter as one mm.4,5,6Abrupt stoppage of retinal vascularization in response to relative hyperoxia constitutes phase 1 of ROP.7Various systemic and ocular factors are known to affect the extent and severity of ROP.8-20These include prematurity, low birth weight, collateral health issues (poor weight gain, sepsis, respiratory distress, apnea), excessive unmonitored oxygen supplementation, etc.8-20 Slow vascular growth has been reported to be an important cause for disease recurrence in babies treated with intravitreal bevacizumab (IVB) for ROP.  21ROP does not require treatment in every stage. The retinopathy does not reach the treatable stage suddenly. The follow-up examination interval depends on the severity of retinopathy, including the stage, location, and presence of plus or pre-plus components besides the postmenstrual age (PMA) and systemic status.22-26The growth rate of retinal vessels in babies with ROP has not been studied enough (Medline search).27

In the present study, we analyzed the rate of vascular growth vis-à-vis the treatment decision in babies with variable ROP severity to determine if this biological marker could help in the decision-making for treatment.

Method

This retrospective study was conducted at a tertiary eye care center serving patients from Eastern India. All the prematurely born babies diagnosed with ROP of various degrees and the retina imaged with good image clarity were included in the study; the study period was from January 2010 to December 2019. Good retina image clarity was defined as the one where the optic disc and vascular endings were visible clearly for calculation. Those with insufficient or unclear images, short follow-ups, stage 4 and 5 ROPs were excluded. The institutional review board approved the study, and it followed the Declaration of Helsinki in research involving human subjects. The eye examinations and fundus imaging were done after written consent from the parents/guardian about imaging and possible use of the anonymized images for teaching and research.

Two pediatric retinal imaging devices were used- RetCam (Clarity Medical Systems, Pleasanton, California) and 3netra neo Digital Wide-field imaging system (Forus Health Pvt Ltd, Bengaluru, India). When needed, the images were enhanced with a red-green image enhancement option available with the device (Figure 1). The retinal imaging in these babies was as per the institute protocol. In brief, fundus images of most babies with ROP of any degree (and some of the babies with prematurity but no ROP) are obtained after informed and signed consent of the parents. The protocol allows obtaining at least basic images covering disc and macula, superior, inferior, superotemporal, inferotemporal, superonasal, inferonasal quadrant as far as possible. The babies were imaged every time they returned for a review. The interval varied from 1 to 6 weeks. The last follow-up varied depending on the time the disease regressed. The majority of the babies were evaluated as ambulatory care. We regularly imaged babies before and after laser procedures; these images were analyzed in the study. Among the multiple visits, we included the last visit image where the disc and the end of blood vessels were imaged simultaneously within a single field. In this study, the images obtained and archived as a part of patient care were analyzed. In group 1 with treatable ROPs, the calculations were done on the images taken on the day of or within a week before treatment.

All the measurements on the images were done from the mid-point of the nasal or temporal margin of the optic disc. The average optic disc horizontal width was taken as 1.05 mm as per the previous reports.4,5,6Retinal arteries start from the optic disc at 16 weeks of gestational age, grow at0.1 mm per day,27and probably reach the optic disc margin at 17 weeks. This presumption was made from the published report of vessel growth of 0.7 Disc diameter (DD)/week after 20 weeks of gestational age (GA).27 We used the caliper option available with the imaging device in the case of RetCam (Figure 2) and a manual measuring scale in the 3netra neo Digital Wide-field imaging system. The PMA (defined as the sum of gestational age and number of days elapsed since birth) in weeks was recorded at the measurement point. The following formula calculated the speed of vascular outgrowth (S) in disc diameter per week: “S=(A/D)/(P-17)”where “A” is the radial distance of the end of blood vessels from the middle of the disc margin, “D” is the horizontal disc diameter, and ‘P’ is the PMA at time of the rate calculation.

We calculated the vascular growth along the superotemporal and inferotemporal quadrants (STQ, ITQ), superonasal and inferonasal quadrants (SNQ, INQ), horizontal nasal (HNQ), and horizontal temporal (HTQ) quadrant, one or more for each eye (total of 6 or fewer measurements per eye). But most of the time, the images were clearer, and calculations could be done most often in superotemporal (428 out of 436 eyes) followed by inferotemporal (379 out of 436 eyes) followed by horizontal temporal quadrant (345 out of 436 eyes).

The babies were divided (Table 1) into Group 1 (Treatment warranting ROP) and Group 2 (spontaneously regressed/low-risk pre threshold ROP). All the classifications were done) as per the CRYOROP, ICROP revised, and ETROP study.28, 29

Group 1 was further sub-divided (Table 1) into 1A (threshold ROP),1B (Aggressive Posterior ROP),1C (hybrid ROP), and 1D (high-risk pre threshold ROP). [ “Hybrid ROP” refers to cases having ridge tissue, similar to staged ROP + flat new vessels, simulating APROP, in the same eye, described by Sanghi et al.30]

Babies born prematurely with an immature retina but did not develop ROP until the last visit were considered controls (Group 3). We excluded babies beyond 38 weeks PMA from the normative data calculation; the terminal ends of the retinal vessels in these babies’ images were difficult to appreciate. Since the horizontal disc diameter was used as the calculation unit in the study, we were aware of the possibilities of difference among different subgroups and consequent bias. So, we calculated the average disc size among the various groups and looked for any statistical difference.

The GA, BW, PMA, and retinopathy status are shown in Table 2. The ROP screening examinations had been done by multiple ROP specialists earlier. But the images were read and analyzed retrospectively by only three of them. The average and range of weekly vascular growth rates were measured for all groups and subgroups by two examiners separately (SP, AP); they had at least one year of experience diagnosing and managing ROP and in the imaging devices used in the study. A third examiner (TRP, ROP specialist with ten years of experience in ROP care) masked the treatment details, cross-checked the measurements, and his decision on the acceptance of one of the two measures in case of a disagreement was final. The examiners were given only one image per eye to do the calculations without showing the images in the other visits. The last follow-up image showing the optic disc and the end of the blood vessel together was selected for Groups 1 and 2. The same was also selected for Group 3 from the images taken on the day or within one week before treatment. We analyzed the inter-observer (between Observer 1 and 2) agreement in calculating the growth rate of blood vessels. The average rates were calculated for the two test groups (Group 2 and 3) and the control group (Group 1). An intragroup comparison was made, and their statistical significance was calculated (Table 1). Each eye’s vascularization rate was arranged from lowest to highest value irrespective of the retinopathy and treatment. Finally, we calculated the strength of the correlation of vascular outgrowth rate with the treatment requirement. We used the ETROP guideline for treatment decisions. The ROP specialist (TRP) decided on the modality of therapy either alone or in combination and included retinal laser, intravitreal anti-vascular endothelial growth factor injection, or surgery.

Statistics: The data were analyzed with SPSS V.21.0 (SPSS Inc, Chicago, IL, USA). Student’s t-test was applied to compare the average speed of vascularization in subjects with and without ROP in different quadrants. The mean, median, range of GA, BW, and PMA measurements in different groups was calculated. The average vascular growth in groups 1 and 2 was compared with the normative control, and the significance of the difference was estimated. The intraclass correlation coefficient test was used to assess the reliability of the observations made by observers 1 and 2. The p <0.05 was taken as statistically significant. The receiver operating characteristic (ROC) curve and the area under the curve (AUC) were used to evaluate the predictive values, and determine the cut-off point in vascularization speed as a predictor of treatment need.

Results

This study recruited 233 babies (bilateral:203 and unilateral:30) and 436 eyes that consisted of 238 eyes (n= 136 babies) in group 1 (treatment warranted), 108 eyes (n=64 babies) in group 2 (spontaneously regressed), and 90 eyes (n=51 babies) in group C (no- ROP) (Table 1). The subgroup of Group 1 was as follows: 1A (threshold ROP)64 eyes; 1B (Aggressive Posterior ROP) 59 eyes; and 1C (hybrid ROP) 28 eyes; 1D (high-risk pre-threshold ROP) 87 eyes. There were 18 babies with each eye falling in a different group. The GA, BW, and PMA calculations of babies in each group are presented in Table 2. Out of 436 eyes, the measurements could be easily made in 428(98.1%),376 (86.2%),344 (78.8%),20 (4.0%),17(3.8%) and 22(5.0%) eyes in STQ, ITQ, HTQ, SNQ, INQ, and HNQ respectively. The examiners succeeded in making calculations in STQ more often than the other quadrants. The inter-observer (between Observer 1 and 2) agreement in the calculation of the rate of growth of blood vessels was considered excellent in the STQ (0.982; 95% Confidence Interval, CI [0.079-0.985]) and good in the ITQ and HTQ (Table.3). The average rate of vascular growth (average of the rates in different quadrants) was 0.719+0.09,0.612+0.10, and 0.49+0.12 DD/week in group 3 (No ROP), in group 2 (Spontaneously regressed), and in group 1 (treatable ROP) eyes respectively (Table 1 and Figure 3). The rate was lowest in subgroup1B, followed by groups A, C, and D. We observed the average horizontal disc diameter (the numerator for speed calculation in the study) of the eyes imaged with Ret Cam was not statistically different (p=0.069) between the three groups (58.98, 61.08, and 58.9 RetCam units for group 1,2, and 3 respectively).

In babies with treatment warranting ROP (Group 1), the vascular growth rate was lower in the nasal than in the temporal quadrant (Table 1). It was lowest in the HNQ (0.22 DD/week) and highest in the STQ (0.52 DD/week). The vascular growth rate in the HNQ was 43.48% of the rate of vascular growth in the STQ and 47.7% of the rate of vascular growth in the HTQ. In the spontaneously regressed and No- ROP group, we did not have enough measurements in the nasal quadrants to compare the speed with the temporal quadrant. The ROC showed that the rate of vascular growth was a significant predictor of the requirement of treatment at a cut off value of ≤0.569(STQ), ≤0.57 (ITQ), and ≤0.542(HTQ) with a chance of correctly predicting the requirement of treatment in 81%,79% and 81% of cases respectively (Table 4 and Figure 4).

Discussion

Retinopathy of prematurity has classically been described as a biphasic disease where the events start with delayed retinal vascular growth, resulting in a peripheral avascular retina (Phase 1). Later, vaso-proliferation (intravitreal angiogenesis) can occur at the junction of the avascular and vascularized retina (phase 2), 7In addition to prematurity, low birth weight, possible genetic factors, other factors (such as extent and duration of oxygen supplementation, postnatal weight gain, sepsis, hyaline membrane disease, cerebral hemorrhage, exchange transfusion, intubation for ten days or longer) also play important roles in the vascular development in prematurely born infants.7,31.A slow rate of retinal vascularization causes a larger avascular retina persisting for a longer period resulting in a greater VEGF load with an increase in the severity of retinopathy. The rate of vascularization is a quantifiable observation. De Larraya et al. have evaluated its efficacy in predicting the requirement of treatment using Indirect ophthalmoscopic evaluations.27They showed that the rate of temporal retinal vascularization was significantly higher in no ROP (0.73+0.22 DD/week) than in stage 1 (0.58 ± 0.22 DD), stage 2(0.46 ± 0.14 DD/week) and stage 3 ROP (0.36 ± 0.18 DD/week). Following a study in 185 babies, they concluded that the slower rate of temporal retinal vascularization could alert a clinician of treatment need. The present study was conducted on a larger sample of patients; we measured the vascular growth in different quadrants around the optic disc, compared the speed of vessel development in ROP subtypes (helps treatment decision in a real-life situation), and also used newer technology such as the red-green enhancement of the images, when required (easier identification of the course and termination of the artery). We used two observers to assure the reproducibility of the results, and compared it with an ROP expert’s final treatment decision.

In our study, the average vascular growth rate in babies without ROP (group 3) was 0.719±0.093DD/week and was similar to two earlier reports.1,2 In our analysis, the vascular growth rate was at least 20% slower in babies who needed treatment compared to those who did not (0.54 to 0.56 DD/week versus 0.72 DD/week). The examiners measured the speeds more easily and more often superotemporally and preferred this quadrant over other quadrants in the speed of vascular growth calculation.

ROP has been described to have nasal-temporal asymmetry.32-34Gallaghar et al. report that at any given point, the retinopathy tends to be 2 to 3mm closer to the disc nasally than temporally.32Nissenkornet al.35 and Fielder et al. 36observed that ROP develops in the nasal retina about two weeks earlier than in the temporal retina. The reasons for this asymmetry in both time and location are unclear. The distance of disc to nasal ora (18.5mm) is shorter, and it is78.7% of the distance of disc to temporal ora (23-24mm) long. 37However, the rate of vascular growth along the horizontal nasal quadrant, as seen in subjects with ROP in this study, was less than 50% of that in the temporal quadrant. This would mean that the distance between the optic disc to ora serrata is shorter nasally than temporally, and the speed of vascular growth is disproportionately less nasally than temporally. As a result, one should expect a larger avascular retina nasally than temporally. This could partly explain the naso-temporal asymmetry in ROP. While we have not used the present study’s information prospectively, it suggests that a slower vascular growth rate should alert the treating ROP specialist for closer follow-up of these babies with extra attention to the correction of systemic risk factors, if any. Our study’s results also prompt us to pay an additional weightage to the nasal quadrant while examining an eye for retinopathy of prematurity.

This study is not without limitations. The measurements of the optic nerve and vascular outgrowths were done on a flat laptop screen, while in reality, the optic nerve head lies on a curved surface, and retinal blood vessels travel on a curved surface. In an inclined image, the optic nerve dimension could be different. We did not have an easy way to calculate the distance of the end of the blood vessels along the vessel wall. So the measurements are actually along the chord length, and it is approximate to the actual length and velocity. Exact measurements of the end of the retinal blood vessels from disc margin without fundus fluorescein angiography (FFA; (currently, we do not have it) is another limitation. FFA has been shown to improve visualization of the peripheral vasculature not easily captured by color fundus photography.38We tried to circumvent the limitation by using red-free image enhancement that aids in better identify the blood vessels. Speed of vascularisation in any quadrant normalized by the optic nerve -ora serrata distance in that quadrant could have supported our claim that the speed is disproportionate in the nasal versus temporal quadrants. Unfortunately, we did not have an ultra-wide field pediatric retina imaging device that could image optic disc and ora serrata in one imaging field. Making a composite image from the posterior pole images and images of the peripheral retina up to ora serrata had its limitations of introducing errors. The problem of image magnification was overcome by using ratios of distance with the disc diameter as the unit of measurement instead of the absolute values. This is a ratio (number of disc diameters per week) and is unaffected by any magnification factor. This was further supported because there was no statistical difference in the individual horizontal disc diameter for measurement (p=0.069). The rate of vascularization could be different in different quadrants measured in the same subject and same time. This was overcome by measuring in specific quadrants in every eye. A good inter-observer correlation coefficient (Table 3) and a uniform time point of calculation (last follow-up visit) further reduced the variabilities.

We had our surprises. Contrary to our expectation that vascular growth rate in eyes with hybrid ROP would be similar to APROP and lower than threshold ROP, it was instead faster. We realize that the eyes with hybrid ROP at times could have large vascular loops and could spread to an anterior zone even though the retina within the loop is avascular.30In the study, the calculations were done at a fixed point of time, assuming that the vascularization rate was uniform over the period studied. This might not be true. The vascular growth depends on many systemic factors that change over time, and so would be the speed. This calls for a prospective study to document the weekly growth in eyes under observation for ROP. Once validated, this parameter would be easily adaptable to clinical settings.

In conclusion, there was a good correlation between the weekly rate of vascular growth and the decision to treat babies with ROP in this study. The vessel growth rate was inversely proportional to the disease severity and was lowest in the APROP group. The growth rate nasally was slower than on the temporal side. Measuring vascular growth in the superotemporal was easier than in other quadrants.

Acknowledgment: Authors acknowledge the help of Mrs. Bhawna Garg in the statistics related to the manuscript.

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Tables 

Table 1. Speed of vascular outgrowth in eyes with   treatable, spontaneously regressed and No ROP
Groups (251 babies,436 eyes)		Description	STQ (n)	ITQ (n)	HTQ (n)	SNQ (n)	INQ (n)	HNQ (n)	All Quadrants together
Group 1 n= 136 babies, 238 eyes	All	Treatable ROP	0.522±0.136 (236)	0.514±0.131 (232)	0.475±0.149 (191)	0.373±0.113 (20)	0.315±0.103 (17)	0.227±0.099 (22)	0.490±0.121
	1A	Threshold ROP (37 babies, 64 eyes)	0.480±0.101 (63)	0.475±0.091 (64)	0.444±0.114 (52)	0.301±0.267 (02)	0.233±0.165 (2)	0.107 (1)	0.461±0.123
	1B	APROP (31 babies,59 eyes)	0.432±0.104 (59)	0.427±0.111 (57)	0.343±0.095 (40)	0.384±0.115 (12)	0.326±0.104 (10)	0.224±0.094 (16)	0.386 ± 0.104
	1C	Hybrid ROP (16 babies,28 eyes)	0.538±0.132 (28)	0.512±0.126 (26)	0.461±0.142 (23)	0.363±0.067 (4)	0.329±0.083 (4)	0.247±0.126 (4)	0.480±0.112
	1D	HRPTH ROP (52 babies, 87 eyes)	0.610±0.124 (86)	0.602±0.118 (85)	0.571±0.132 (76)	0.4±0.043 (02)	0.306 (01)	0.328 (01)	0.592±0.069
Group 2(64 babies,108 eyes)		Spontaneously regressed ROP	0.632±0.105 (105)	0.613±0.104 (96)	0.589±0.108 (97)	–	–	–	0.612±0.106
Group 3,(51 babies,90 eyes)		NO ROP	0.721±0.090 (87)	0.705±0.093 (51)	0.731±0.097 (57)	–	–	–	0.719±0.093

APROP-Aggressive Posterior ROP, HNQ-Horizontal nasal quadrant, INQ-Inferonasal quadrant, HRPTH ROP-High Risk Prethreshold Retinopathy of Prematurity, HTQ-Horizontal temporal quadrant, ROP-Retinopathy of Prematurity ,SNQ- Superonasalquadrant, STQ- Superotemporalquadrant

Table 2.Gestational Age (GA), Birth weight(BW) and Post Menstrual age (PMA)  at calculation of babies within 3 sub groups in the present study
Parameters	Treatable ROP as a whole(Gr 1)	Subgroup 1A (Threshold)	Subgroup 1B (APROP)	Subgroup 1C (Hybrid)	Subgroup 1D (HRPTH)	Spontaneous  Regression (Gr 2)	NO ROP (Gr 3)
GA in wks (Range,Avg±SD)	23-36 30.091± 1.97	25.28-34 29.72±1.98	26.71-34 30.07±1.48	28.29-35 30.95±2.09	23-36 30.089±2.098	25-38 30.60±2.03	29-38 32.44±2.17
BW in g (Range,Avg±SD)	640-2100 1261.61±292.56	640-1900 1218.98±290.57	850-1700 1210.33±205.11	1000-1900 1319.28±265.71	840-2100 1309.19±305.85	700-2500 1432.33±363.69	900-2400 1634.54±324.45
PMA in wks at calculation (Range,Avg±SD)	29-44.57 36.52±2.37	34-43.57 37.92±2.29	31-41.71 35.06±2.14	33-39.14 35.74±2.13	29-44.57 36.73±3.02	31-45.97 38.65±2.92	32.85-41 37.49±1.72

ROP-Retinopathy of Prematurity, SD-Standard deviation,Post menstrual age is defined as a sum of gestational age and number of days elapsed since birth.

Table 3: Interobserver co-relation co-efficient between observer 1 and 2
Treatment Required	STQ		ITQ		HTQ
	Interobserver correlation	95% Confidence interval	Interobserver correlation	95% Confidence interval	Interobserver correlation	95% Confidence interval
Single Measures	0.9664	0.9593 to 0.9722	0.7789	0.7128 to 0.8282	0.7804	0.7261 to 0.8231
Average measures	0.9829	0.9792 to 0.9859	0.8757	0.8323 to 0.9060	0.8767	0.8413 to 0.9030

HTQ-Horizontal temporal quadrant; ITQ-Inferotemporal quadrant; STQ-Superotemporal quadrant

Values less than 0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability, and values greater than 0.90 indicate excellent reliability

Table 4. Receiver operating characteristic curve of STQ, ITQ and HTQ for predicting requirement of treatment
Treatment Required	STQ	ITQ	HTQ
Area under the ROC curve (AUC)	0.817	0.791	0.819
Standard Error	0.0202	0.0232	0.0229
95% Confidence interval	0.777 to 0.853	0.747 to 0.831	0.774 to 0.858
P value	<0.0001	<0.0001	<0.0001
Cut off	≤0.569	≤0.578	≤0.542
Sensitivity (95% CI)	66.95% (60.6 – 72.9%)	73.71% (67.5 – 79.3%)	67.37% (60.2 – 74.0%)
Specificity (95% CI)	82.29% (76.1 – 87.4%)	71.23% (63.2 – 78.4%)	83.66% (76.8 – 89.1%)
PPV (95% CI)	82.3% (76.1 – 87.4%)	80.3% (74.3 – 85.4%)	83.7% (76.8 – 89.1%)
NPV (95% CI)	66.9% (60.6 – 72.9%)	63% (55.2 – 70.4%)	67.4% (60.2 – 74.0%)
Diagnostic accuracy	73.83%	72.75%	74.63%

Legends to figures

Figure 1 (Left) Color fundus image of the left eye taken with 3netra neo Digital Wide-field imaging system (Forus Health Pvt Ltd) showing few tortuous vascular loops around optic disc. Nasally they hardly extend beyond 1.5 Disc diameter from nasal border of the optic disc. (Right) Same eye after  red green enhancement making the blood vessels stand out with better clarity

Figure 2. Snap shot image showing the method of measurement of vascular growth done on the  laptop screen and the calliper option available with RetCam (Clarity medical Inc).The eye shown here  shows threshold retinopathy of Prematurity (ROP) in zone I.Thedisc dimensions are measured both horizontally and vertically and the ends of the blood vessels are measured in supero,infero and horizontal temporal quadrants.

Figure 3. Diagram showing the average speed of retinal vascularization in babies with Retinopathy of Prematurity of varying severity.

Figure 4. The Receiver operating characteristic curve (ROC) to find out area under the curve and cut-off point of vascular growth predicting a decision to treat. ROC curves above the diagonal line are considered to have reasonable discriminating ability to predict requirement of treatment. The Discriminatory power of the rate of Vascular growth (Area under curve 0.819,0.791,0.819, 95% confidence interval-66.95,73.71 and 63.37 respectively for STQ, ITQ and HTQ) was acceptable rate of vascular growth was a significant predictor of requirement of treatment at a cut off value of ≤0.569 (STQ), ≤0.57 (ITQ) and ≤0.542 (HTQ) with a chance of correctly predicting the requirement of treatment in 81,79 and 81% of cases respectively

Table 1. Speed of vascular outgrowth in eyes with   treatable, spontaneously regressed and No ROP

Table 2. Gestational Age, Birth weight and Post Menstrual age at time of measurements in babies within the three sub groups in the present study

Table 3. Inter-observer co-relation co-efficient between observer 1 and 2

Table 4. Receiver operating characteristic curve of supero, infero and horizontal temporal quadrant for predicting requirement of treatment