Characteristics

Ideal requirement

Methods

Significance

Ref.

Surface morphology

Smooth surface, Spherical shape.

SEM, TEM, Electron microscopy, Optical microscopy, Photon correlation microscopy.

To access uniformity of particle size and surface characteristics.

[85]

Angle of repose

Less than 30

Funnel method

To determine flow properties.

[86]

Vesicle size

Globular in shape, <10 μm

Malvern master sizer,

Dynamic light scattering.

Analyses variation in scattered light intensity.

[87]

Entrapment efficiency

>50 %

Ultrafiltration centrifugation, HPLC.

Important for accessing drug-loading capacity.

[88]

Zeta potential

+30 mv

Malvern zeta sizer.

For proniosomes stability

[89]

Polydispersity index

0.1-0.4 (<0.5)

Dynamic light scattering

Measure of homogeneity

[90]

Refractive index

>1.476 as the refractive index of tear fluid ranges from 1.34 to 1.36.

Abbe refractometer

Detection of potential patient pain following administration due to impaired eyesight.

[91]

Viscosity

Between 2 and 3 mPa.s

Brookfield viscometer

Viscosity should be optimized to provide residence, not blurred vision.

[92]

pH

6.5-8.5

pH meter

Reduces eye irritability.

[93]

Surface tension

Between 40-50 mN/m

Tensiometer

Important to measure the performance of the formulation.

[94,95]

In vitro drug release

As per the need

Dialysis membrane or Franz diffusion cell

To determine the amount of drug release

[53]

Ocular irritation evaluation

The formulation should be safe and tolerable for ocular administration.

Draize test

To determine any congestions and or irritation of the cornea, iris, and conjunctiva caused by the formulation.

[96]

In vivo pharmacodynamic study

The formulation should provide the optimum therapeutic effect of the drug within the required time.

In vivo studies on living subjects

To evaluate the ocular bioavailability of the drug.

[97]

Stability

The formulation should be stable throughout its shelf life under the given storage condition.

As per ICH guidelines

To determine the effect of storage on the size, PDI, and zeta potential.

[53]