Review of Literature on Intraductal Meibomian Gland Probing with Insights from the Inventor and Developer: Fundamental Concepts and Misconceptions

Figures & data

Figure 1 (1a and b) Performing supraorbital and infraorbital nerve block using JBP 33 gauge 4 mm long nanoneedles. (2a and b) Jojoba anesthetic ointment consisting of 8% lidocaine and 25% jojoba is taken from a refrigerated jar and applied to the lid margin for 10 minutes. This may be repeated. (3) The probing set-up at the slit lamp with an assistant to steady the patient for good visualization. (4) View through the slit lamp microscope of probing upper (a) and lower (b) lid Meibomian glands. (5) Meibography guided probing using the Mediworks S390L WDR FireFly Digital Slit Lamp from Eyefficient (Aurora, Ohio), demonstrating a 4 mm probe within the central duct (a), a sterile MicroTube Stent within the central duct for retrieval of meibum (b) and the retrieved meibum inside the MicroTube removed from within the gland (c). Reproduced from Maskin SL, Alluri S. Meibography guided intraductal meibomian gland probing using real-time infrared video feed. Br J Ophthalmol. 2020;104(12):1676; with permission from BMJ Publishing Group Ltd.²¹ (6) An alternative approach to obtaining a virgin sample of meibum by allowing the meibum to travel through the MicroTube Stent for collection and analysis. Arrow shows a drop of meibum at the distal end of the MicroTube Stent.²²

Notes: 1a-b, 2a-b, 3, 4a-b: Courtesy of Steven L Maskin MD; 5a-c: Reproduced from Maskin SL, Alluri S Meibography guided intraductal meibomian gland probing using real-time infrared video feed British Journal of Ophthalmology 2020;104:1676–1682 with permission from BMJ; 6: Reproduced from Maskin, SL, Warren NA. Your Dry Eye Mystery Solved: Reversing Meibomian Gland Dysfunction, Restoring Hope. Yale University Press, 2022 with permission from Yale University Press.

Table 1 Summary of Independent MGP Studies and Their Result

Study^A	Date	Design	Refractory to Prior Treatment^B	Follow-Up^C	Study Treatment^D	n= Pts (Eyes) [Lids] {Glnd}^E	Improvement in MGP Treatment Group Compared to Control, Baseline, or Other Treatment
							Symptoms (Subjective)	Signs (Objective)^F
Kheirkhah et al^Citation3	2020	DB RCT	3 Mo LH, WC, Top, Syst	1 Mo	MGP+Bleph+PT ^3a,3b,3c,3d,3e,3f	13 (26)	Compared to Baseline
							SANDE p=0.002	No significance ^3g,3h,3i
							OSDI p=0.02
					MGP+GenT+PT^3a, 3b,3c,3d,3e,3f	14 (28)	Compared to Baseline
							SANDE p=0.01	No significance ^3g,3h,3i
					Control: Sham MGP+GenT+PT^3b,3d,3e,3f	14 (28)	Compared to Baseline
							No significance	LT p=0.02^3g,3h,3i
Huang et al^Citation7	2019	SB RCT	1 Yr WC, Mas, AT	12 Wk	MGP ^7a,7b,7c,7d,7e	15 (30)	Compared to Baseline
							SPEED p<0.001	TBUT p<0.001; >5 sec: 36.67%
							Relief: 100% of pts	CFS p<0.001
							Worse symptoms: 0% of pts	MG p<0.001
							SPEED ≤9, 26.67% pts	LMV p=0.001
								OA p<0.001
								LT p=0.001
							Compared to IPL
								LT p<0.001
				6 Mo	Retreat required	3, 20%
				9 Wk	IPL (3 sessions)+AT daily^7f	14 (28)	Compared to Baseline
							SPEED p<0.001	TBUT p<0.001; >5 sec: 17.86%
							Relief: 85.7% of pts	CFS p<0.001
							Worse symptoms: 14.8% of pts	MG p=0.003
							SPEED ≤9, 14.29% pts	LMV p=0.006
								OA p<0.001
								LT p=0.003
				6 Mo	Retreat required (3 additional sessions)	5, 35.7%
				12 Wk	MGP+IPL^7a,7b,7c,7d,7f	14 (28)	Compared to Baseline
							SPEED p<0.001	TBUT p<0.001; >5 sec: 92.9%
							SPEED ≤9, 64.29% pts	CFS p<0.001
								MG p<0.001
								LMV p=0.001
								OA p<0.001
								LT p<0.001
							Compared to MGP
							SPEED p=0.012	TBUT p=0.012
								MG p<0.001
								LMV p<0.001
								OA p=0.016
							Compared to IPL
							SPEED p=0.003	TBUT p=0.003
								MG p=0.002
								LMV p=0.002
								LT p<0.001
				6 Mo	Retreat required	0%	Compared to MGP
							SPEED p=0.01
							Compared to IPL
							SPEED p=0.004
Ma and Lu^Citation8	2016	OL RCT	WC, Mas, AT	1 Mo	MGP+Top Ster 3x/day+PT^8a,8b,8c	25 (46)	Compared to Baseline
							Var Symp p<0.01	LM p<0.05
								MG p<0.05
							Relief in 1 day: 76% of pts (19/25)	TBUT p<0.05
								FS p<0.05
								Immediate release of meibum: (38/46)
							Compared to Control
							Var Symp p<0.001	LM p<0.001^8d,8e
								MG p <0.001^8d,8f
								TBUT p=0.0293^8d,8g
					Control: Top Ster 3x/day+PT	24 (45)	Compared to Baseline
							Var Symp p<0.01	LM p<0.05^8d,8e,8f,8g,8h
								MG p<0.05
							Relief in 1 day: 0% of pts (0/24)	TBUT p<0.05
								FS p<0.05
Incekalan et al^Citation9	2019	OL RCT	AT	3 Mo	MGP+CT^9a,9b,9c,9d	20 (40) {8 lower lid, 12 upper lid}	Compared to Baseline
							OSDI p<0.05	Sch1 p<0.05
								TBUT p<0.05
								OS p<0.05
								MQ p<0.05
					Retreat	0%^9e		ME p=0.0001
							Compared to Control
							OSDI faster p=0.0001	Sch1 faster p=0.0001
								TBUT faster p=0.014
								OS faster p=0.0001
								MQ faster p=0.034
								ME faster p=0.0001
					CT: WC, Mas, LH, AT, CP, O3, OAZ.	20 (40)	Compared to Baseline
							OSDI p<0.05	Sch1 p<0.05
								TBUT p<0.05
								OS p<0.05
								MQ p<0.05
								ME p=0.0001
Wladis^Citation5	2012	PL	AT, OA, Diet	6 Mo	MGP^5a,5b	10 (20) [40]	Compared to Baseline
							OSDI p<0.05	Decreased gland blockage, keratitis, thickened lids^5c
					(Retreat: 0%)	0%
Fermon et al^Citation14	2015	PL	CT	6 Mo	MGP^14a,14b,14c,14d, 14e	16 (16)	Compared to Baseline
							VA p<0.001^14g	TBUT p<0.0001^14g
							BlCo p=0.008^14g
							Pho p<0.001^14g
					Retreat^14f	2, 12.5%
Nakayama et al^Citation13	2015	PL	2.5, 3, or 8 Yr HA, DS, Re, LH, MCG, PP, Of, RC, Lv, Ox, or SSRI	1 Mo	MGP^13a,13b	3 (3) [6] {60}	Compared to Baseline
							DEQS: 2 cases improved^13c	MLL, MV, LI: All cases improved
								TBUT: 2 cases improved
Sik Sarman et al^Citation10	2016	PL	6 Mo CT, Mas	3 Mo	MGP^10a,10b,10c,10d+ CT^10e	30 (58) [116]	Compared to Baseline
							OSDI: significant^10h	TBUT p<0.001
					Treatment: 1x	8, 26.7%		CH p<0.0001
					Retreat: 2x^10f,10g	18, 60%		LMV p=0.004
					Retreat: 3x ^10f,10g	3, 10%
					Retreat: 4x^10f,10g	1, 3.3%
Nirupama et al^Citation11	2019	PL	8 Wk CT		MGP^11a, 11b, 11c +CT^11d	30	Compared to Baseline
				1 Mo			OSDI: 73% of pts (22/30)^11e	TBUT: 73% of pts (22/30)
								LMC: 73% of pts (22/30)
				3 Mo	Retreat	8, 27%
				6 Mo			OSDI p=0.0001: 93.3% of pts (28/30)^11e	TBUT p=0.0001: 93.3% of pts (28/30)
								LMC: 100% of pts (30/30)
Syed and Sutula^Citation4	2017	RCR	4 Wk WC, LH, AI	1–64 Wk^4a	MGP^4b,4c,4d	41 [70]	Compared to Baseline
				1 Wk			Rapid symptom improvement: 91.4% of lids [64/70]^4f
				52 Wk	Retreat	[1/13]=7.7%^4e

Notes: General Comments:

• ^AAll of the studies employed different methods and no study followed developer’s published and recommended probing protocol¹⁹ exactly.

• ^BAll of the subjects in each study were refractory to standard treatment or were administered standard treatment, some for at least 4 weeks (Syed and Sutula⁴) and one up to 8 years (Nakayama et al¹³) prior to enrolling in the study. Therefore, the baseline of each study, at a minimum, is prior failed treatment. (Suggesting otherwise by the review authors¹⁶ is a significant error and oversight in their analysis.)

• ^CNote the short duration of many of the studies. SLM studies have shown that patients with lid tenderness experience relief instantaneously upon probing, whereas those with other symptoms resolve over 2-3 months as gland functionality resumes gradually after probing. Patients who were reprobed 1 week or 1 month after initial probing may have been reprobed prematurely, or may have suffered with untreated comorbid diseases that led to gland re-obstruction.

• ^DStudy protocols were significantly different from each other and from the developer’s published and recommended protocol.¹⁹ Some investigators used probes of their own design and all of these were larger in diameter than Maskin probes. No study started probing with a 1mm probe to determine the angle of entry. Some studies used probes of only 1 length which limited the ability to probe deeper within the gland where, glands with MGD may remain obstructed with periductal fibrosis. Adjunctive treatment varied from study to study and was not necessarily based on an individual patient’s specific symptoms or comorbidities, but instead was prescribed to all patients. Therefore, patients may have been prescribed unnecessary treatment or treatment to which they were sensitive, or not prescribed needed adjunctive treatment for comorbidities.

• ^EIn at least one study both lids were not treated, and in some studies not all glands in a lid were treated, even though both lids and all glands contribute to both signs (eg TBUT) and symptoms (eg gritty, burning) of MGD.

• ^FIn some cases we include the finding, but not the p-value if it was not reported in the study.

Kheirkhah et al³

• ^3aOnly upper lids were probed.

• ^3b2% lidocaine jelly was used to anesthetize lids. In cases where anesthesia was inadequate, MGP-treated lids were injected with anesthetic which can cause microtrauma and lid tenderness unresolved at the time of follow-up, whereas sham-MGP lids were not injected.

• ^3cRandomly assigning patients to the MGP + Blephamide or MGP + GenTeal groups ignores adjunctive treatment that patients would actually need and would influence patient outcomes considerably.

• ^3dDuring the course of the study, patients may have developed sensitivity to Blephamide or GenTeal ointment, which would have influenced patient outcomes.

• ^3ePatients continued prior medications (minus steroids) as well as warm compresses and lid hygiene.

• ^3fMGP + GenTeal lids injected with anesthesia prior to treatment may have resulted in micro trauma to lids and resulting tenderness.

• ^3gBecause only the upper lid was treated, but both upper and lower lids can contribute to symptoms, results may be skewed.

• ^3hLid tenderness evaluation is not clear raising several questions. Was topical anesthetic used prior to evaluation to prevent confounding findings from a tender ocular surface? How did the investigators manage focal versus regional versus whole lid tenderness? Were these findings identified and if so, how were they managed statistically? Were the findings combined or was there an attempt to differentiate among types?

• ³ⁱThe investigators compared results of treatment or sham treatment to baseline only, not across groups.

Syed and Sutula⁴

• ^4aAccording to the investigators, “The follow-up period ranged from 1 to 64 weeks (mean 12.9 weeks).

• ^4bIn addition to administering topical anesthetic (topical proparacaine to the cornea, a cotton pledget soaked in 4% lidocaine and placed in the fornix) the investigators also injected 1% lidocaine with epinephrine “using a transconjunctival approach into the fornix centrally, medially, and laterally. Supplemental subcutaneous injection near the eyelid margin” was also injected. The MGP developer’s protocol-recommended¹⁹ topical anesthetic is a topical jojoba anesthetic ointment containing 8% lidocaine.

• ^4cInvestigators started with a 2mm probe to “dilate each orifice sequentially” followed by use of the 4mm probe. A short, 1mm length probe was not used initially to locate the angle of entry.

• ^4dAccording to the investigators, probing was well tolerated and there were no complications.

• ^4e52 weeks after initial treatment, one of the 13 long-term follow up patients underwent retreatment of 1 eyelid due to a return of symptoms.

• ^4fAccording to the investigators, “Sixty-four treatments (91.4%) resulted in subjective relief immediately after the procedure, typically within 1 week. These patients reported an improvement or resolution of their primary symptoms. The remaining 6 cases (8.6%) did not result in immediate symptom relief”.

Wladis⁵

• ^5aFor anesthesia, lids were injected with 2% lidocaine with epinephrine.

• ^5bMaskin probes were not used. Instead, the investigator used a hyfrecator tip (without applying electrical current) of unreported diameter and length. The hyfrecator tip is designed to destroy superficial tissue or control bleeding, and is not designed and dimensioned specifically for passing through the fixed resistance and scar tissue encountered with Meibomian gland probing. Thus, probing with a hyfrecator tip may lead to excessive trauma and hemorrhage.

• ^5cAfter probing, all patients reported improvement in “discomfort, visual effect, and tearing, and documented a decreased need for topical lubrication…Nine of ten patients (90%) were able to successfully discontinue the use of doxycycline after their 1-month postoperative visit. No complications were noted through a 6-month follow-up period, and no patients required repeat probing”.

Huang et al⁷

• ^7aThe investigators did not use Maskin probes. Probes were 4.5 mm in length and the blunt end was 0.12 mm in diameter (compared to 0.076 mm diameter Maskin probes). The hollow tube for lavage was 2.0 mm in length and had a wider diameter 0.16 mm (compared to the Maskin MicroTube 0.110 mm diameter). A single length and larger diameter probe can increase discomfort and hemorrhage.

• ^7b4% lidocaine was injected into the upper and lower lids which caused subcutaneous bruising in several patients and can cause persistent lid pain potentially skewing treatment results.

• ^7cA short, 1mm length probe was not used initially to locate the angle of entry.

• ^7dAfter probing glands were expressed with a paddle, rather than a Maskin roller.

• ^7eA hollow tube was used to lavage glands with 0.1% dexamethasone and 0.25% amikacin. Tobradex ointment was also applied on the day of probing.

• ^7fA single IPL treatment consists of three separate IPL sessions.

Ma and Lu⁸

• ^8aMaskin probes were not used. Instead, investigators used a 100-µm-diameter wire not dimensioned specifically for the Meibomian gland which could make finding the angle of entry difficult.

• ^8bOnly 2mm-long probes were used. Probes of this length can buckle causing difficulty in finding the angle of entry. A 1mm Maskin probe is shorter and stiffer, dimensioned and designed to facilitate finding the angle of entry.

• ^8cA 0.25% oxybuprocaine hydrochloride drop was applied to the inferior conjunctival fornix. The MGP developer’s protocol-recommended¹⁹ topical anesthetic is a topical jojoba anesthetic ointment containing 8% lidocaine.

• ^8dThe investigators stated, “In group I, [MGP + topical steroid] 76% (19/25) of the patients had symptom relief 1 day after probing before the administration of any additional medical treatment. However, in group II [topical steroid alone], there was no significant improvement on the first day without any additional medical treatment”.

• ^8eThe investigators stated, “At 1 week and 1 month, all scores in group I were lower than those in group II”.

• ^8fThe investigators stated, “Abnormalities of the lid margin were significantly improved in both groups after 1 week and 1 month of treatment, especially in lid margin congestion and orifice plugs. There were significant differences in the lid margin score 1 month after treatment between groups…”.

• ^8gThe investigators stated, “The meibum grade significantly improved in both groups, and the improvement was more significant in group I than in group II at the 1-week and 1-month follow-up visits”.

• ^8hThe investigators stated, “One month after treatment, the increase in TBUT in group I was more significant than that of group II”.

Incekalan et al⁹

• ^9a5 glands in the upper lid and 5 glands in the lower lid were assessed for expressibility. Meibum quality was assessed in the central 8 glands of the lower lid.

• ^9bNot all glands in a lid were probed. 8 glands in the lower lid and 12 glands in the upper lid were probed.

• ^9cMaskin probes were not used.

• ^9dA 0.5% proparacaine hydrochloride drop was dropped into the inferior conjunctival fornix. The MGP developer’s protocol-recommended¹⁹ topical anesthetic is a topical jojoba anesthetic ointment containing 8% lidocaine.

• ^9eNo patients required retreatment at 3 months.

Sik Sarman, et al¹⁰

• ^10aProparacaine hydrochloride 0.5% was used as an anesthetic. The MGP developer’s protocol-recommended¹⁹ topical anesthetic is a topical jojoba anesthetic ointment containing 8% lidocaine.

• ^10bMaskin probes were not used.

• ^10cProbing started with a 2-mm length probe. A short, 1mm length probe was not used initially to locate the angle of entry.

• ^10dLonger probes (2.5-, 4-, or 6-mm length) were only used if resistance was met with the 2mm probe. However, glands may present with no resistance within the distal 2 mm, but deeper obstruction may still be present.

• ^10eAfter MGP, all patients uniformly used topical antibiotics, corticosteroids, and artificial tears, applied warm compresses, and massaged eyelids with a cotton-tip applicator.

• ^10fPatients with symptoms 1 week after initial treatment were retreated.

• ^10gThe investigators noted the chronic recurrent course of the disease and advanced MGD in patients as the reason why 73.3% of patients required retreatment.

• ^10hThe investigators did not provide a p-value for OSDI improvement but noted that, “Mean OSDI scores were 79.7 ± 19.4 at baseline and 22.9 ± 13.5 at 3 months (range, 0–100). The later OSDI scores showed a significant improvement in all the patients”.

Nirupama, et al¹¹

• ^11aNot all glands were probed. According to the investigators, “The area of eyelid selected to be probed was the one with severe symptoms and with dilated ducts”.

• ^11bProparacaine hydrochloride 0.5% was used as an anesthetic. The MGP developer’s protocol-recommended¹⁹ topical anesthetic is a topical jojoba anesthetic ointment containing 8% lidocaine.

• ^11cOnly 4mm probes were used. A short, 1mm length probe was not used initially to locate the angle of entry.

• ^11dAdjunct therapy included antibiotic drops prescribed for 5 days after probing to all patients. Patients were instructed to apply warm compresses twice a day for 4–5 minutes and massage lids with a cotton tip applicator “to drain secretions”.

• ^11eThe investigators reported that, “Patients noted increased comfort in lid excursion. The surface of the eye was smoother and cooler as described by some of them”.

Nakayama et al¹³

• ^13aNot all glands in a lid were probed. Instead, “10 orifices at even intervals were selected to be penetrated for each eyelid”.

• ^13bOnly 2mm probes were used. A short, 1mm length probe was not used initially to locate the angle of entry.

• ^13cOn the 100-point DEQS scale, 1 case improved by 14.9 points and 1 case improved by 0.9 points.

Fermon et al¹⁴

• ^14aOne eye was treated and the other eye was used as a control.

• ^14bOnly glands which were believed to be occluded, defined as “glands which do not transilluminat”, were probed. “The mean number of treated glands was 26”.

• ^14cMaskin probes (2mm and 4mm) were used but without the initial use of a 1mm probe.

• ^14dThe investigators stated, “None of the patients referred significant discomfort during the intervention and no associated complications emerged”.

• ^14eNo additional treatments for blepharitis were administered.

• ^14fThe investigators stated, “In the 6 month follow-up, only 2 treated eyes (12.5% of sample) required retreatment (new probing) due to reactivation of symptoms and recurring glandular occlusion”. This may have been due to inadequately managed comorbidities since no other treatments were administered.

• ^14gThe investigators stated, “All patients (100%) exhibited statistically significant improvement in the 4 variables of the study at the six-month assessment”. These 4 variables were objective TBUT and subjective visual acuity, blink comfort, and photophobia.

Acronyms and Abbreviations:Design: DB, double blind; RCT, randomized controlled trial; SB, single blinded; OL, open label; PL, prospective longitudinal; RCR, retrospective chart review.

Prior Treatment: LH, lid hygiene; WC, warm compresses or eyelid warming; Top, topical treatment; Syst, systemic treatment; Mas, lid massage; AT, artificial tears; OAZ, oral azithromycin; OA, oral antibiotics; Diet, dietary modifications; CT, conventional treatment; HA, hyaluronic acid; DS, diquafosol sodium; Re, Rebamipide; MCG, moisture chamber glass; PP, punctum plugs; Of, ofloxacin ointment; RC, repair of chalasis; Lv, levofloxacin; Ox, oxacalcitriol ophthalmic ointment; SSRI, selective serotonin reuptake inhibitors; AI, topical anti-inflammatory.

Refractory/Follow-up: Mo, months; Yr, year; Wk, week.

Study Treatment: MGP, Meibomian gland probing; Bleph, blephamide; PT, prior treatment or prior conservative treatment; GenT, GenTeal PM Night-Time ointment; IPL, intense pulsed light; TopSter, topical steroid; CT, conventional treatment; WC, warm compress; Mas, lid massage; LH, lid hygiene; AT, artificial tears; CP, ciprofloxacin; 03, oral omega-3 fatty acids; OAZ, oral azithromycin.

n=: n, number of subjects; Pts, number of patients; (Eyes), number of eyes; [Lids], number of lids, {Glnd}, number of glands.

Symptoms, subjective symptoms: SANDE, Symptom Assessment in Dry Eye; OSDI, Ocular Surface Disease Index; SPEED, Standardized Patient Evaluation of Eye Dryness; Var Symp, various symptoms; DEQS, Dry Eye-Related Quality-of-Life Score; VA, visual acuity; BlCo, comfort when blinking; Pho, photophobia.

Signs: LT, lid tenderness; TBUT, tear break-up time; LM, lid margin abnormalities; CFS, corneal fluorescein stain; MG, meibum grade; LMV, lid margin vascularization; OA, orifice abnormality; Sch1, Schirmer 1 test; FS, fluorescein stain; OS, ocular surface Oxford score; MQ, meibum quality; ME, meibum expressibility; MLL, meibum lipid level; MV, meibum viscosity; LI, lipid interferometry; CH, conjunctival hyperemia; LMC, lid margin congestion.

Figure 2 Probe findings form of a patient.

Notes: Reproduced from Maskin, SL, Warren NA. Your Dry Eye Mystery Solved: Reversing Meibomian Gland Dysfunction, Restoring Hope. Yale University Press, 2022 with permission from Yale University Press.²²

Figure 3 Confocal microscopy image of Meibomian gland distal duct showing disruption of the normally well demarcated external duct wall by fibrovascular tissue invasion. A prominent blood vessel is seen inside the oval. The disruption of the duct wall is indicated by the solid arrow showing a “step off”. This gland had not been probed. (Courtesy of SLM.).

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