Thyroid-related ophthalmopathy is an inflammatory auto-immune process with  frequent extrathyroidal manifestations [1]. 

These extrathyroid manifestations peak at approximately 6 to 24 months following the onset and have a significant impact on visual parameters [2]. Inflammatory mediators released by lymphocytes drive orbital fibroblasts and produces glycosaminoglycans. Deposition of GAG will lead to interstitial edema and enlargement of extraocular muscles with secondary mechanical effects [3]. Increased muscle volume gives rise to intraorbital pressure at the apex. It will not only causes compression of optic nerve but also  obstruction of venous outflow. The compression of optic nerve precipitate optic neuropathy. Symptoms and signs of dysthyroid optic neuropathy leads to alteration of visual parameters ,relative afferent pupillary defect and visual field defects, .  Venous obstruction is proved to be a contributing factor leading to proptosis, periorbital swelling, and chemosis. Quantitative information on the flow velocity within orbital vessels  is  obtained by colour doppler imaging (CDI) in patients with thyroid-associated eye disease .Colour Doppler sonography is widely used in the evaluation of orbital  vessels [4,5,6].  The contrast sensitivity function has proved a important tool for detecting visual disturbances when Snellen acuity fails to show comparable dysfunction in glaucoma, [7] retinal disease [8]. In this study we evaluated the effect of early thyroid ophthalmopathy on visual parameters - visual acuity, color vision, contrast sensitivity and correlated with ocular blood flow. In  early stages of thyroid ophthalmopathy. The current literature on refractive changes in endocrine ophthalmopathy is limited. Chandrasekaran et al. (2006) reported the myopic shift following orbital decompression in progressive endocrine ophthalmopathy [9].

AIM- we evaluated the effect of early thyroid ophthalmopathy on visual parameters - visual acuity, intra-ocular pressure, color vision, contrast sensitivity and correlated with ocular blood flow.

We conducted a prosepective, comparative, interventional  study after ethical approval from institutional ethical board.  Total 30 patients are included, who visited in, Department of Ophthalmology, sp medical college associated group of hospital between June 2022 to May 2023. Patients with exposure keratopathy and optic neuropathy were excluded. All the patients underwent a complete ophthalmic examination including best corrected Snellen visual acuity, color vision by Ishihara pseudochromatic plates, contrast sensitivity by pelli robson chart, pupillary reflexes, funduscopy, proptosis measurement by Hertl ophthalmometer, ocular motility by the degree of clinical gaze restriction,  and clinical activity score . Color Doppler Imaging (CDI) was performed in 60 orbits of 30 patients with thyroid eye disease.  Color Doppler Imaging was done in masked fashion by one radiologist experienced in sonography. Examinations were done with a colour doppler sonographic unit (Toshiba SSA-270A, Tokyo) using a 7.5-MHz linear phased-array transducer.

Thyroid eye disease was considered to be present if eyelid retraction occurred together with objective evidence of thyroid dysfunction or exophthalmus or optic nerve dysfunction or extraocular muscle involvement. If eyelid retraction was absent, then thyroid eye disease was diagnosed when exophthalmos, optic nerve involvement, or restrictive extraocular myopathy coexisted with thyroid dysfunction. All clinical assessments were performed within 1 month of the CDI. Among 30  patients, 16 patients with  Graves’ hyperthyroidism,  10 with hypothyroid, and four were   euthyroid.  In this study, patients were divided into 3 groups on the basis of the clinical activity score (CAS) of Mourits. [10] Group A included 13 patients with CAS value ‘‘zero’’, group B included 10  patients with CAS value 1 to 2; group C included 7 patients with CAS value 3 or greater. Visual parameters are assessed for each group  and correlated with ocular blood flow.

The LogMAR chart is designed to enable more accurate estimates of acuity as compared to other acuity charts (e.g., the Snellen chart). The Snellen chart, which dates back to 1862, is also commonly used to estimate visual acuity. A Snellen score of 6/6 (20/20), indicating that an observer can resolve details as small as 1 minute of visual angle, corresponds to a LogMAR of 0 (since the base-10 logarithm of 1 is 0); a Snellen score of 6/12 (20/40), indicating an observer can resolve details as small 2 minutes of visual angle, corresponds to a LogMAR of 0.3 (since the base-10 logarithm of 2 is 0.3), and so on.[10]

The Pelli-Robson contrast sensitivity test (Clement Clarke International Ltd.) is a wall chart measuring 90 x 60 cm (36 x24 inches). The chart comprises 8 lines of letters with different contrasts. Each line has 6 letters; the first 3 letters (a triplet) on the left have more contrast than the 3 letters on the right. The contrast also decreases downward from line to line. The size of the letters is 4.9 x 4.9 cm (2 x 2 inches). The letters on the left of the top line have the highest contrast, 1 or 100%, and the letters on the right of the bottom line have the lowest contrast, 0.006 or 0.6%. On the result paper (Figure 2), the values of logarithmic contrast sensitivity (1/contrast) are given. There are different sets of letters on each side of the chart. The manufacturer recommends a testing distance of 1 m, which corresponds to a spatial frequency of about 1 cycle per degree (cpd). An add of .75 diopter (D) can be used if distance correction is needed. The logarithmic contrast sensitivity value of the last triplet of which at least 2 letters are correctly seen is marked as the result. The luminance of the test should be 85 candelas/m2 (cd/m2); the accepted range is 60 to 120 cd/m2 .

Color vision in every subject was assessed by psuedoisochromatic plates.

Table 1 showing comparison of visual parameters in Group A , B and C

Table 1 –showing all visual parameters are normal except contrast sensivity . CSF was affeceted in group c but that was not with satitically significant difference.

Table-2 showing comparison of ocular blood flow in Group A , B and C

CRA- Central Retinal Artery, SOV- Superior ophthalmic vein, CRV- Central Retinal vein, OA- Ophthalmic Artery, PSV- Peak systolic velocity, EDV- End diastolic volume, RI- Resistive Index

Ocular blood flow as well as visual parameters were found not to be affected in group a and b. Ocular blood flow in group c was slightly affected without statically significance.

Visual parameters remain unaffected in group c except contrast sensitivity with slight change.

Table-3 showing correlation between visual parameters and ocular blood flow

Ocular blood flow varies with the orbital inflammation in TED. Although there is few reference showing refractive change associated with Graves' ophthalmopathy. In thyroid eye disease, astigmatism may possibly be caused by soft-tissue fibrosis in the supero-lateral orbital region [11]. In our study ocular blood flow showing no change in group a and b but slight changes were seen in group c with clinical activity score more than 2

In cases of thyroid pathology visual acuity and refractive changes develop due to the proliferation of retrobulbar cells, causing exophthalmos. Myopia in thyroid eye disease may be because of  eye-ball remodeling and  thyroid hormones causing change in the tonicity of ciliary muscle [11).

In 5 % of people, visual field test and color vision are  found to be affected    [12, 13, 14]. At subclinical stage, identification of active congestive symptoms and  any change in visual parameters are important for starting early treatment  [15]. Noninvasive and sensitive diagnostic tests are required for detecting early change of DON before any  irreversible visual deficit.  [16]. In our prospective study, we evaluated the function of optic nerve by contrast sensitivity function test, color vision and visual acuity . we found that it is was unaffected in early stage of thyroid eye disease patients in group a and group b. CST WAS SLIGHTLY AFFECTED IN GROUP C WITH  NO STATICALLY SIGNIFICANT DIFFERENCE.. Suttorp-Schulten et al. examined 38 eyes with DON and 34 eyes with only TAO by contrast sensitivity function test and they compared the contrast sensitivity results of these TAO patients with or without DON and those of 74 healthy subjects [17]. They found that the CSFs of the patients with DON significantly decreased and the TAO patients without DON also had lower contrast sensitivity level than the healthy subjects. The sensitivity loss of the patients with DON was higher at lower frequencies (1–5 c/deg) than that of the patients without DON [19]. So, they reported that CSF test may be beneficial for the discrimination of the TAO patients complicated with DON from those without DON [17]. Mourits et al. found that the CSF WAS deteriorated even in the patients WITH conserved visual acuity AND COLOR VISION  AND  observed that CSF was improved after orbital decompression surgery in 33 eyes [18].

Grave's ophthalmopathy IS FOUND TO BE ASSOCIATED WITH NUMBER OF ophthalmic manifestations. Five percent of the patients WITH endocrine exophthalmos SUFFERED FROM secondary glaucoma DUE TO RAISED orbital venous pressure [19]. Several studies have REPORTED that the patients with primary open angle glaucoma have BEEN REPORTED WITH sensitivity loss in temporally modulating gratings[20-24]. de Marco et al. compared the CSFs of 20 eyes with uncomplicated TAO, those of 14 eyes with increased IOP more than 24 mmHg, and those of 12 eyes with DON and CSFs of 40 healthy eyes [25) the effect of the elevated intraocular pressure over the CSFs was not known IN HYROID EYE DISEASE PATIENTS . In our study, all PATIENTS WITH THYROID EYE DISEASE had no secondary glaucoma or elevated IOP; the mean IOP IN OUR patients a was 14.82 mmHg.. Thereby, the effect of  IOP  over the CSFs was eliminated in our study.

We used Ishihara color plates for the evaluation of color vision in our study because it is a routine clinical test used for detecting whether optic neuropathy exists or not in a patient.  these tests could probably detect the impairment of optic nerve functions in early phase of the disease as contrast sensitivity function test. For this reason, further multicentered studies with larger sample which are supported by various clinical sensitive tests are needed. Optic nerve stress in early stage of TAO may change the thoughts and the aspects of the clinicians for the disease. In active stage of TAO, the signs of inflammation are pronounced and the inflammation regresses in inactive stage. Determination of the disease stage is important for decision of the treatment.. In these settings most of the patients are followed up on a wait-and-see policy unless severe inflammation and DON develop. Hence, early presentation of optic nerve stress may change the treatment protocols of the disease and early diagnosis and treatment may alter the course and progression of the disease and may lead to obtaining better visual and cosmetic outcome.

Crowding of orbital space IN TAO may interfere with ocular perfusion, unchecked progression may lead to irreversible damage in visual field and visual parameters. The orbital perfusion can be ASSESED BY b measuring  blood flow velocities in the superior ophthalmic vein (SOV), ophthalmic artery (OA), central retinal artery (CRA), and posterior ciliary artery by color doppler imaging. The orbital and ocular perfusion fluctuates during the course of TED. Orbital congestion is reflected by decrease or reversal of sov and  active phase by high blood flow velocities of the oa and cra.

we concluded that there was little change in ocular blood flow was noted in group c with no statical significant difference along with little change in csf. sequential evaluation of orbital hemodynamic changes and change visual parameters can supplement the clinical scoring systems for monitoring and planning intervention in ted.